superconductor

SEMINAR ON SUPERCONDUCTIVITY AND ITS APPLICATION ON SCIENCE AND TECHNOLOGY. ABSTRACT: As a consequence, the past decade or two of superconductor discovery can best be summarized by the phrase “expect the unexpected”. Superconductivity is an electrical resistance of exactly zero which occurs in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetismand atomic spectral lines, superconductivity is a quantum mechanical phenomenon. The behavior of superconductor suggests that electron pairs are coupling over a range of hundreds of nanometers, three orders of magnitude larger than the lattice spacing, called cooper pairs. These coupled electrons can take the character of a boson and condense into the ground state. This clear explanation is given by BCS theory. hereby after reading this paper you will easily get the clear ideas of Josephson Devices-BCS theory-applications such as super conducting generators, SEMS, superconducting cables. CHAPTER ONE 1.0 INTRODUCTION A superconductor is a material that can conduct electricity or transport electrons from one atom to another with no resistance. This means no heat, sound or any other form of energy would be released from the material when it has reached "critical temperature" (Tc), or the temperature at which the material becomes superconductive. Unfortunately, most materials must be in an extremely low energy state (very cold) in order to become superconductive. Research is underway to develop compounds that become superconductive at higher temperatures. Currently, an excessive amount of energy must be used in the cooling process making superconductors inefficient and uneconomical. Superconductors come in two different flavors: type I and type II. (1) Type I Superconductors A type I superconductor consists of basic conductive elements that are used in everything from electrical wiring to computer microchips. At present, type I superconductors have Tcs between 0.000325 °K and 7.8 °K at standard pressure. Some type I superconductors require incredible amounts of pressure in order to reach the superconductive state. One such material is sulfur which, requires a pressure of 9.3 million atmospheres (9.4 x 1011 N/m2) and a temperature of 17 °K to reach superconductivity. Some other examples of type I superconductors include Mercury - 4.15 °K, Lead - 7.2 °K, Aluminum - 1.175 °K and Zinc - 0.85 °K. Roughly half of the elements in the periodic table are known to be superconductive. (1) Type II Superconductors A type II superconductor is composed of metallic compounds such as copper or lead. They reach a superconductive state at much higher temperatures when compared to type I superconductors. The cause of this dramatic increase in temperature is not fully understood. The highest Tc reached at stardard pressure, to date, is 135 °K or -138 °C by a compound (HgBa2Ca2Cu3O8) that falls into a group of superconductors known as cuprate perovskites. This group of superconductors generally has a ratio of 2 copper atoms to 3 oxygen atoms, and is considered to be a ceramic. Type II superconductors can also be penetrated by a magnetic field whereas a type I can not 1.2 What is a superconductor? Superconductors are materials that conduct electricity with no resistance. This means that, unlike the more familiar conductors such as copper or steel, a superconductor can carry a current indefinitely without losing any energy. They also have several other very important properties, such as the fact that no magnetic field can exist within a superconductor. Superconductors already have drastically changed the world of medicine with the advent of MRI machines, which have meant a reduction in exploratory surgery. Power utilities, electronics companies, the military, transportation, and theoretical physics have all benefited strongly from the discovery of these materials. A brief history of superconductors The first discovery of a superconductive material took place in 1911 when a Dutch scientist named Heike Kammerlingh Onnes, who was also the first person to liquefy helium, and reached temperatures as low as 1.7 kelvin (K). In the 1960s, two unrelated discoveries made closely together ushered in a new era in which practical superconducting devices were developed and commercialized: one was the discrovery of NbTi superconductor, which provided the first material for the practical manufacture of superconducting wire and shaped components; the second was the Josephson junction, which continues to provide the basis for a variety of unique electronic devices. To this day, the largest successful applications of superconductors remains the powerful electromagnets used in Magnetic Resonance Imaging (MRI) systems (over 22,000MRI magnets made) and research magnets, and the RF accelerator cavities used in high energy physics experiments. Despite the enormous success of NbTi and similar materials, even broader application of superconductors has been restricted by the requirement for cooling to very low temperatures (1.5 - 5K)using liquid helium. In late 1986 J. Georg Bednorz and K. Alexander Müller, two researchers at IBM's Zurich Lab, discovered announced an oxide material that superconducted at 30K. These two researchers were awarded the Nobel Prize in Physics 1987 for their work. Then, in 1987, Paul Chu at the University of Houston discovered YBCO, which became a superconductor at just 90K. Because 90K can be reached using liquid nitrogen, a common industrial refrigerant, these discoveries opened up for the first time the potential for a much wider range of devices. Over the next several months, discoveries of BSCCO and TBCCO brought the transition temperature of superconductors up to 127K. This discovery of these "High Temperature Superconductors" sparked vast interest, and an entire industry dedicated to the research and commercial development of these materials and their applications has emerged. Today, an enormous range of devices are under development for both low and high temperature superconductors. International competition is strong in these materials, and current efforts involve many facets of the electronics, communications, power, medical technology, transportation, military, and materials processing industries. Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. It was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing through a loop of superconducting wire can persist indefinitely with no power source. In 1986, it was discovered that some cuprate-perovskite ceramic materials have a critical temperature above 90 K (−183 °C). Such a high transition temperature is theoretically impossible for a conventional superconductor, leading the materials to be termed high-temperature superconductors. Liquid nitrogen boils at 77 K, and superconduction at higher temperatures than this facilitates many experiments and applications that are less practical at lower temperatures. CHAPTER TWO 2.0 LITERATURE REVIEW This is the first macroscopic theorysuper conductivity observed that mercury to explain the concept of superacts as superconductor below 4.2 k conductivity London proposed that theretemperature. The resistance of his mercury are two types of conduction electronsample did not tend toward some constants namely super electrons, normal electrons.value as the temperature was reduced Here, the super electrons are not subjectedbelow 4.2k. At 4.15k, the DC resistance of to any lattice scattering and they movethe sample is completely vanished. freely over the lattices points. But the total conduction electron density is equal to In 1913, he wrote that no doubt sum of super electrons and normalwas left of the existence of a new state of electrons.mercury in its resistance has practicallyvanished superconducting state. 2. Ginsburg- Landau Theory-1950: The most striking and well known This theory gives the idea that theproperty of superconductor is their lack of super conducting state is characterized byelectrical resistance. In 1933, Meissner and a single complex wave function. ThisOchsen field found, most surprisingly, that theory describes the properties of superwhen a pure metal is cooled through its conducting state such as meissner effect,superconducting transition temperature in zero electrical resistance and Type II superthe presence of magnetic field all magnetic conductor.flux is expelled from within its bulk.Spontaneous exclusion of magnetic flux 3. Bardeen, Cooper and Schriefferfrom a superconductor could not be quite (BCS) theory:complete of course, even in principle This is the first microscopic theorycurrents in metals arises from the flow of based on quantum theory. They introducedelectrons and no physical current sheet can a new pair of electrons called cooper pairbe made indefinitely thin due to repulsion and they are responsible for the superforce between these electrons. Hence the conductivity.temperature at which a normal conductorloses its resistivity and become a Principle:superconductor is known as transitiontemperature (or) critical temperature. This theory states that the electrons experience a special type of attractive At the transition temperature, the interaction, overcoming the coulombfollowing physical changes are observed. forces of repulsion between them, as a result Cooper pairs (i.e.,) electrons pairs 1. The electrical resistance drops to are formed. At low temperature these zero. pair’s moves without scattering (i.e.,) 2. The magnetic flux lines are without any resistance through the lattice excluded from the material. points and the material becomes 3. There is a discontinuous change in superconductor. Here the electrons- lattice- specific heat. electrons interaction should be stronger 4. Further there are also a small than electron-electron interaction. change in thermal conductivity and the volume of the material. The superconducting state of a metal may be considered to be resulting With the help of reference given by from cooperative behavior of conductiononnes, the succeeding scholars proposed electrons. Such a cooperation or coherencethe following theories. 2.1 Classification There are many criteria by which superconductors are classified. The most common are: • Response to a magnetic field: A superconductor can be Type I, meaning it has a single critical field, above which all superconductivity is lost; or Type II, meaning it has two critical fields, between which it allows partial penetration of the magnetic field. • By theory of operation: It is conventional if it can be explained by the BCS theory or its derivatives, or unconventional, otherwise. • By critical temperature: A superconductor is generally considered high temperature if it reaches a superconducting state when cooled using liquid nitrogen – that is, at only Tc > 77 K) – or low temperature if more aggressive cooling techniques are required to reach its critical temperature. • By material: Superconductor material classes include chemical elements (e.g. mercury or lead), alloys (such as niobium-titanium, germanium-niobium, and niobium nitride), ceramics (YBCO and magnesium diboride), or organic superconductors (fullerenes and carbon nanotubes; though perhaps these examples should be included among the chemical elements, as they are composed entirely of carbon). 2.1.1. Elementary properties of superconductors Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature, critical field, and critical current density at which superconductivity is destroyed. On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have exactly zero resistivity to low applied currents when there is no magnetic field present or if the applied field does not exceed a critical value. The existence of these "universal" properties implies that superconductivity is a thermodynamic phase, and thus possesses certain distinguishing properties which are largely independent of microscopic details. 2.1.2. Zero electrical DC resistance Electric cables for accelerators at CERN. Both the massive and slim cables are rated for 12,500 A. Top: conventional cables for LEP; bottom: superconductor-based cables for the LHC The simplest method to measure the electrical resistance of a sample of some material is to place it in an electrical circuit in series with a current source I and measure the resulting voltage V across the sample. The resistance of the sample is given by Ohm's law as R = V / I. If the voltage is zero, this means that the resistance is zero. Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years. Theoretical estimates for the lifetime of a persistent current can exceed the estimated lifetime of the universe, depending on the wire geometry and the temperature.[3] In a normal conductor, an electric current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat, which is essentially the vibrational kinetic energy of the lattice ions. As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance. The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists of bound pairs of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum amount of energy ΔE that must be supplied in order to excite the fluid. Therefore, if ΔE is larger than the thermal energy of the lattice, given by kT, where k is Boltzmann's constant and T is the temperature, the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation. In a class of superconductors known as type II superconductors, including all known high-temperature superconductors, an extremely small amount of resistivity appears at temperatures not too far below the nominal superconducting transition when an electric current is applied in conjunction with a strong magnetic field, which may be caused by the electric current. This is due to the motion of magnetic vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero. 2.2. Superconducting phase transition Behavior of heat capacity (cv, blue) and resistivity (ρ, green) at the superconducting phase transition In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature Tc. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K to less than 1 K. Solid mercury, for example, has a critical temperature of 4.2 K. As of 2009, the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB2),[7][8] although this material displays enough exotic properties that there is some doubt about classifying it as a "conventional" superconductor.[9] Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown. Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high critical temperature. Similarly, at a fixed temperature below the critical temperature, superconducting materials cease to superconduct when an external magnetic field is applied which is greater than the critical magnetic field. This is because the Gibbs free energy of the superconducting phase increases quadratically with the magnetic field while the free energy of the normal phase is roughly independent of the magnetic field. If the material superconducts in the absence of a field, then the superconducting phase free energy is lower than that of the normal phase and so for some finite value of the magnetic field (proportional to the square root of the difference of the free energies at zero magnetic field) the two free energies will be equal and a phase transition to the normal phase will occur. More generally, a higher temperature and a stronger magnetic field lead to a smaller fraction of the electrons in the superconducting band and consequently a longer London penetration depth of external magnetic fields and currents. The penetration depth becomes infinite at the phase transition. The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as e−α/T for some constant, α. This exponential behavior is one of the pieces of evidence for the existence of the energy gap. The order of the superconducting phase transition was long a matter of debate. Experiments indicate that the transition is second-order, meaning there is no latent heat. However in the presence of an external magnetic field there is latent heat, because the superconducting phase has a lower entropy below the critical temperature than the normal phase. It has been experimentally demonstrated[10] that, as a consequence, when the magnetic field is increased beyond the critical field, the resulting phase transition leads to a decrease in the temperature of the superconducting material. Calculations in the 1970s suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field. In the 1980s it was shown theoretically with the help of a disorder field theory, in which the vortex lines of the superconductor play a major role, that the transition is of second order within the type II regime and of first order (i.e., latent heat) within the type I regime, and that the two regions are separated by a tricritical point.[11] The results were strongly supported by Monte Carlo computer simulations.[12] 2.2.1 Meissner effect When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected. The Meissner effect does not cause the field to be completely ejected but instead the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material. The Meissner effect is a defining characteristic of superconductivity. For most superconductors, the London penetration depth is on the order of 100 nm. The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenz's law, when a changing magnetic field is applied to a conductor, it will induce an electric current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from this—it is the spontaneous expulsion which occurs during transition to superconductivity. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law. The Meissner effect was given a phenomenological explanation by the brothers Fritz and Heinz London, who showed that the electromagnetic free energy in a superconductor is minimized provided where H is the magnetic field and λ is the London penetration depth. This equation, which is known as the London equation, predicts that the magnetic field in a superconductor decays exponentially from whatever value it possesses at the surface. A superconductor with little or no magnetic field within it is said to be in the Meissner state. The Meissner state breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value Hc. Depending on the geometry of the sample, one may obtain an intermediate state[13] consisting of a baroque pattern[14] of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value Hc1 leads to a mixed state (also known as the vortex state) in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electric current as long as the current is not too large. At a second critical field strength Hc2, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called fluxons because the flux carried by these vortices is quantized. Most pure elemental superconductors, except niobium and carbon nanotubes, are Type I, while almost all impure and compound superconductors are Type II. 2.2.2. London moment Conversely, a spinning superconductor generates a magnetic field, precisely aligned with the spin axis. The effect, the London moment, was put to good use in Gravity Probe B. This experiment measured the magnetic fields of four superconducting gyroscopes to determine their spin axes. This was critical to the experiment since it is one of the few ways to accurately determine the spin axis of an otherwise featureless sphere. 2.3. History of superconductivity Superconductivity was discovered on April 8, 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently produced liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared. In the same experiment, he also observed the superfluid transition of helium at 2.2 K, without recognizing its significance. The precise date and circumstances of the discovery were only reconstructed a century later, when Onnes's notebook was found.[16] In subsequent decades, superconductivity was observed in several other materials. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. Great efforts have been devoted to finding out how and why superconductivity works; the important step occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect.[17] In 1935, Fritz and Heinz London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current.[18] 2.3.1. London theory The first phenomenological theory of superconductivity was London theory. It was put forward by the brothers Fritz and Heinz London in 1935, shortly after the discovery that magnetic fields are expelled from superconductors. A major triumph of the equations of this theory is their ability to explain the Meissner effect,[19] wherein a material exponentially expels all internal magnetic fields as it crosses the superconducting threshold. By using the London equation, one can obtain the dependence of the magnetic field inside the superconductor on the distance to the surface.[20] There are two London equations: The first equation follows from Newton's second law for superconducting electrons. 2.3.2. Conventional theories (1950s) During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957).[21][22] In 1950, the phenomenological Ginzburg-Landau theory of superconductivity was devised by Landau and Ginzburg.[23] This theory, which combined Landau's theory of second-order phase transitions with a Schrödinger-like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Abrikosov showed that Ginzburg-Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau had received the 1962 Nobel Prize for other work, and died in 1968). The four-dimensional extension of the Ginzburg-Landau theory, the Coleman-Weinberg model, is important in quantum field theory and cosmology. Also in 1950, Maxwell and Reynolds et al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element.[24][25] This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity. The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper and Schrieffer.[22] This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. The BCS theory was set on a firmer footing in 1958, when N. N. Bogolyubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian.[26] In 1959, Lev Gor'kov showed that the BCS theory reduced to the Ginzburg-Landau theory close to the critical temperature.[27][28] Generalizations of BCS theory for conventional superconductors form the basis for understanding of the phenomenon of superfluidity, because they fall into the lambda transition universality class. The extent to which such generalizations can be applied to unconventional superconductors is still controversial. 2.4. Further history The first practical application of superconductivity was developed in 1954 with Dudley Allen Buck's invention of the cryotron.[29] Two superconductors with greatly different values of critical magnetic field are combined to produce a fast, simple, switch for computer elements. Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated. Much later, in 1955, G.B. Yntema [30] succeeded in constructing a small 0.7-tesla iron-core electromagnet with superconducting niobium wire windings. Then, in 1961, J.E. Kunzler, E. Buehler, F.S.L. Hsu, and J.H. Wernick [31] made the startling discovery that, at 4.2 degrees kelvin, a compound consisting of three parts niobium and one part tin, was capable of supporting a current density of more than 100,000 amperes per square centimeter in a magnetic field of 8.8 tesla. Despite being brittle and difficult to fabricate, niobium-tin has since proved extremely useful in supermagnets generating magnetic fields as high as 20 tesla. In 1962 T.G. Berlincourt and R.R. Hake [32][33] discovered that alloys of niobium and titanium are suitable for applications up to 10 tesla. Promptly thereafter, commercial production of niobium-titanium supermagnet wire commenced at Westinghouse Electric Corporation and at Wah Chang Corporation. Although niobium-titanium boasts less-impressive superconductng properties than those of niobium-tin, niobium-titanium has, nevertheless, become the most widely-used “workhorse” supermagnet material, in large measure a consequence of its very-high ductility and ease of fabrication. However, both niobium-tin and niobium-titanium find wide application in MRI medical imagers, bending and focusing magnets for enormous high-energy-particle accelerators, and a host of other applications. Conectus, a European superconductivity consortium, estimated that In 2014, global economic activity, for which superconductivity was indispensable, amounted to about five billion euros, with MRI systems accounting for about 80% of that total. In 1962, Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator.[34] This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. It is used in the most accurate available measurements of the magnetic flux quantum Φ0 = h/(2e), where h is the Planck constant. Coupled with the quantum Hall resistivity, this leads to a precise measurement of the Planck constant. Josephson was awarded the Nobel Prize for this work in 1973. In 2008, it was proposed that the same mechanism that produces superconductivity could produce a superinsulator state in some materials, with almost infinite electrical resistance. CHAPTER THREE 3.0. High-temperature superconductivity Timeline of superconducting materials Main article: High-temperature superconductivity Until 1986, physicists had believed that BCS theory forbade superconductivity at temperatures above about 30 K. In that year, Bednorz and Müller discovered superconductivity in a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987).[6] It was soon found that replacing the lanthanum with yttrium (i.e., making YBCO) raised the critical temperature to 92 K.[36] This temperature jump is particularly significant, since it allows liquid nitrogen as a refrigerant, replacing liquid helium.[36] This can be important commercially because liquid nitrogen can be produced relatively cheaply, even on-site, avoiding some of the problems (such as so-called "solid air" plugs[clarification needed]) which arise when liquid helium is used in piping.[37][38] Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics. There are currently two main hypotheses – the resonating-valence-bond theory, and spin fluctuation which has the most support in the research community.[40] The second hypothesis proposed that electron pairing in high-temperature superconductors is mediated by short-range spin waves known as paramagnons. Since about 1993, the highest temperature superconductor was a ceramic material consisting of mercury, barium, calcium, copper and oxygen (HgBa2Ca2Cu3O8+δ) with Tc = 133–138 K.[43][44] The latter experiment (138 K) still awaits experimental confirmation, however. In February 2008, an iron-based family of high-temperature superconductors was discovered. Hideo Hosono, of the Tokyo Institute of Technology, and colleagues found lanthanum oxygen fluorine iron arsenide (LaO1-xFxFeAs), an oxypnictide that superconducts below 26 K. Replacing the lanthanum in LaO1−xFxFeAs with samarium leads to superconductors that work at 55 K. Fundamental Properties of Superconductors A superconducting or superfluid phase is considered a different thermodynamical phase when compared to the normal state that exists when the temperature T>T_c, where T_c means the critical temperature below which the superconducting or superfuid state appears. For example, liquid 4He under its vapor pressure becomes superfluid at T_c=2.17 K. So, the passage from one state to the other is called a phase transition, and it is accompanied by a strong increase of the specifi heat when the temperature is near T_c, with a strong release of entropy. This phenomena, experimentally seen, leads to the formation of a more ordered state of matter (see also precedent video). Fundamentally, a superconductor is a conductor that has undergone a phase transition to a lower energy state below the critical temperature T_c, characterized by the appearance of groups of paired electrons, the so called Cooper pairs, carrying electrical current without any resistance and responsible, among other properties, of perfect diamagnetism. We may distinguish two types of superconductors. A Type I supercondcutor, is characterized by the following properties [1]: • zero electrical resistance and perfect diamagnetism at a temperature below T_c. Normally, at temperatures above T_c this material is a normal metal, although not a very good conductor; • perfect diamagnetism, also called Meissner effect, the magnetic field stays outside the material, cann’t penetrate the material. Curiosly enough, if you appply an external magnetic field B_app above a given critial magnetic field, B_c, the material suffers a transition from superconductor to normal state. An approximate functional dependence on temperature for this critical magnetic field is given by And what is the diamagnetic property of matter? This property is a kind of negative magnetism. This effect was studied in the framework of classical mechanical by Paul Langevin in 1905 [2], using previous and revolutionary ideas proposed formerly by André-Marie Ampère[3] and Wilhelm Weber [4] (nowadays we barely talk about these two great men of science that really use their minds for the advancement of science and the progress of mankind…). Langevin found, in the classic framework provided by Ampère and Weber, that N electrons moving in orbits around the nucleus at an average distance , such that the (constant and negative) magnetic susceptibility χ is given by The magnetic susceptibility is the ratio of M/H, where M is the magnetization field and H the magnetic field. The susceptibility χ is slightly negative for diamagnets, but acquires small positive values for paramagnetic substances (e.g., ), and is strongly positive for ferromagnetics substances (e.g., Fe). It can be shown that a material constitute of paramagnetic ions with magnetic moment μ, obeys the Curie-Weiss law: where n means the concentration of paramagnetic ions, Θ is the Curie-Weiss constant () . when perfect diamagnetism is achieved, χ=-1, that is, the magnetization M is directed opposite to the H field, cancelling it, M=-H. For example, when a superconductor with spherical form is placed nearby the poles of a magnet, it results a superposition of the applied magnetic field B_app, and the resulting dipole field, giving a curvature of the magnetic field lines of the form. The dipole result when a uniform permanent magnetization M is parallel to the axis Oz (see Section 5.10 in the textbook of J. D. Jackson [4]). Besides perfect diamagnetism, the other important property of the superconducting state is its zero resistance. In ideal conditions, an electric current established in a loop of supercuncting wire will last indefenitely. The surface resistance of the material with a current flowing along a film of thickness d, must satisfy the condition where ρ is the electric resistivity, h is the Planck constant and e is the absolute charge of the electron. Applications Of superconductivity Superconductors are already used in many fields: electricity, medical applications, electronics and even trains. They are used in laboratories, especially in particle accelerators, in astrophysics with the use of bolometers, in ultrasensitive magnetic detectors called SQUIDs, and in superconducting coils to produce very strong magnetic fields. However, they need to be cooled to very low temperatures, which restricts their use in our everyday life. But new applications are already operational in laboratories and will be able to spread to our cities and our homes if the cooling process becomes less expensive or, better, if we discover superconducting materials that do not require any cooling. If this happens, we can expect an actual revolution in energies and environment on the one side, and transportation and computer science on the other. Technological applications of superconductivity Superconducting magnets are some of the most powerful electromagnets known. They are used in MRI/NMR machines, mass spectrometers, and the beam-steering magnets used in particle accelerators. They can also be used for magnetic separation, where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries. In the 1950s and 1960s, superconductors were used to build experimental digital computers using cryotron switches. More recently, superconductors have been used to make digital circuits based on rapid single flux quantum technology and RF and microwave filters for mobile phone base stations. Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. SQUIDs are used in scanning SQUID microscopes and magnetoencephalography. Series of Josephson devices are used to realize the SI volt. Depending on the particular mode of operation, a superconductor-insulator-superconductor Josephson junction can be used as a photon detector or as a mixer. The large resistance change at the transition from the normal- to the superconducting state is used to build thermometers in cryogenic micro-calorimeter photon detectors. The same effect is used in ultrasensitive bolometers made from superconducting materials. Other early markets are arising where the relative efficiency, size and weight advantages of devices based on high-temperature superconductivity outweigh the additional costs involved. Promising future applications include high-performance smart grid, electric power transmission, transformers, power storage devices, electric motors (e.g. for vehicle propulsion, as in vactrains or maglev trains), magnetic levitation devices, fault current limiters, enhancing spintronic devices with superconducting materials,[48] and superconducting magnetic refrigeration. However, superconductivity is sensitive to moving magnetic fields so applications that use alternating current (e.g. transformers) will be more difficult to develop than those that rely upon direct current. Some of the technological applications of superconductivity include: • the production of sensitive magnetometers based on SQUIDs • fast digital circuits (including those based on Josephson junctions and rapid single flux quantum technology), • powerful superconducting electromagnets used in maglev trains, Magnetic Resonance Imaging (MRI) and Nuclear magnetic resonance (NMR) machines, magnetic confinement fusion reactors (e.g. tokamaks), and the beam-steering and focusing magnets used in particle accelerators • low-loss power cables • RF and microwave filters (e.g., for mobile phone base stations, as well as military ultra-sensitive/selective receivers) • fast fault current limiters • high sensitivity particle detectors, including the transition edge sensor, the superconducting bolometer, the superconducting tunnel junction detector, the kinetic inductance detector, and the superconducting nanowire single-photon detector • railgun and coilgun magnets • electric motors and generators[1] Contents • 1 Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) • 2 High-temperature superconductivity (HTS) o 2.1 HTS-based systems o 2.2 Holbrook Superconductor Project o 2.3 Tres Amigas Project o 2.4 Magnesium diboride • 3 Notes Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) The biggest application for superconductivity is in producing the large volume, stable, and high magnetic fields required for MRI and NMR. This represents a multi-billion US$ market for companies such as Oxford Instruments and Siemens. The magnets typically use low temperature superconductors (LTS) because high-temperature superconductors are not yet cheap enough to cost-effectively deliver the high, stable and large volume fields required, notwithstanding the need to cool LTS instruments to liquid helium temperatures. Superconductors are also used in high field scientific magnets. High-temperature superconductivity (HTS) The commercial applications so far for high temperature superconductors (HTS) have been limited. HTS can superconduct at temperatures above the boiling point of liquid nitrogen, which makes them cheaper to cool than low temperature superconductors (LTS). However, the problem with HTS technology is that the currently known high temperature superconductors are brittle ceramics which are expensive to manufacture and not easily formed into wires or other useful shapes.[2] Therefore the applications for HTS have been where it has some other intrinsic advantage, e.g. in • low thermal loss current leads for LTS devices (low thermal conductivity), • RF and microwave filters (low resistance to RF), and • increasingly in specialist scientific magnets, particularly where size and electricity consumption are critical (while HTS wire is much more expensive than LTS in these applications, this can be offset by the relative cost and convenience of cooling); the ability to ramp field is desired (the higher and wider range of HTS's operating temperature means faster changes in field can be managed); or cryogen free operation is desired (LTS generally requires liquid helium that is becoming more scarce and expensive). HTS-based systems HTS has application in scientific and industrial magnets, including use in NMR and MRI systems. Commercial systems are now available in each category.[3] Also one intrinsic attribute of HTS is that it can withstand much higher magnetic fields than LTS, so HTS at liquid helium temperatures are being explored for very high-field inserts inside LTS magnets. Promising future industrial and commercial HTS applications include Induction heaters, transformers, fault current limiters, power storage, motors and generators, fusion reactors (see ITER) and magnetic levitation devices. Early applications will be where the benefit of smaller size, lower weight or the ability to rapidly switch current (fault current limiters) outweighs the added cost. Longer-term as conductor price falls HTS systems should be competitive in a much wider range of applications on energy efficiency grounds alone. (For a relatively technical and US-centric view of state of play of HTS technology in power systems and the development status of Generation 2 conductor see Superconductivity for Electric Systems 2008 US DOE Annual Peer Review.) Holbrook Superconductor Project The Holbrook Superconductor Project is a project to design and build the world's first production superconducting transmission power cable. The cable was commissioned in late June 2008. The suburban Long Island electrical substation is fed by about 600-meter-long underground cable system consists of about 99 miles of high-temperature superconductor wire manufactured by American Superconductor, installed underground and chilled with liquid nitrogen greatly reducing the costly right-of-way required to deliver additional power.[4] Tres Amigas Project American Superconductor was chosen for The Tres Amigas Project, the United States’ first renewable energy market hub.[5] The Tres Amigas renewable energy market hub will be a multi-mile, triangular electricity pathway of superconductor electricity pipelines capable of transferring and balancing many gigawatts of power between three U.S. power grids (the Eastern Interconnection, the Western Interconnection and the Texas Interconnection). Unlike traditional powerlines, it will transfer power as DC instead of AC current. It will be located in Clovis, New Mexico. Magnesium diboride Magnesium diboride is a much cheaper superconductor than either BSCCO or YBCO in terms of cost per current-carrying capacity per length (cost/(kA*m)), in the same ballpark as LTS, and on this basis many manufactured wires are already cheaper than copper. Furthermore, MgB2 superconducts at temperatures higher than LTS (its critical temperature is 39 K, compared with less than 10 K for NbTi and 18.3 K for Nb3Sn), introducing the possibility of using it at 10-20 K in cryogen-free magnets or perhaps eventually in liquid hydrogen.[citation needed] However MgB2 is limited in the magnetic field it can tolerate at these higher temperatures, so further research is required to demonstrate its competitiveness in higher field applications. Transportation. The rapid and efficient movement of people and goods, by land and by sea, poses important logistical, environmental, land use and other challenges. Superconductors are enabling a new generation of transport technologies including ship propulsion systems, magnetically levitated trains, and railway traction transformers. Medicine. Advances in HTS promise more compact and less costly Magnetic Resonance Imaging (MRI) systems with superior imaging capabilities. In addition, Magneto-Encephalography (MEG), Magnetic Source Imaging (MSI) and Magneto-Cardiology (MCG) enable non-invasive diagnosis of brain and heart functionality. Industry. Large motors rated at 1000 HP and above consume 25% of all electricity generated in the United States. They offer a prime target for the use of HTS in substantially reducing electrical losses. Powerful magnets for water remediation, materials purification, and industrial processing are also in the demonstration stages. Communications. Over the past decade, HTS filters have come into widespread use in cellular communications systems. They enhance signal-to-noise ratios, enabling reliable service with fewer, more widely-spaced cell towers. As the world moves from analog to all digital communications, LTS chips offer dramatic performance improvements in many commercial and military applications. Scientific Research. Using superconducting materials, today’s leading-edge scientific research facilities are pushing the frontiers of human knowledge - and pursuing breakthroughs that could lead to new techniques ranging from the clean, abundant energy from nuclear fusion to computing at speeds much faster than the theoretical limit of silicon technology. Commercial Application of Superconductors Superconductivity: Applications in Electric Power Today’s power grid operators face complex challenges that threaten their ability to provide reliable service: steady demand growth; aging infrastructure; mounting obstacles to siting new plants and lines; and new uncertainties brought on by structural and regulatory reforms. Advances in high temperature superconductivity (HTS) over the past two decades are yielding a new set of technology tools to renew this critical infrastructure, and to enhance the capacity, reliability and efficiency, of the nation’s power system. The US Power Grid Under Stress Power industry experts in the United States are widely agreed that today’s aging power grid must be strengthened and modernized. Utilities must cope with a growth in the underlying level of demand driven by our expanding, high technology-intensive economy. Consumers in the digital age have rising expectations and requirements for grid reliability and power quality. Competitive reforms have brought about new patterns of power flows. EPRI (the Electric Power Research Institute) has estimated that $100 billion must be spent over the next ten years to achieve and maintain acceptable levels of electric reliability. Uses for Superconductors Magnetic-levitation is an application where superconductors perform extremely well. Transport vehicles such as trains can be made to "float" on strong superconducting magnets, virtually eliminating friction between the train and its tracks. Not only would conventional electromagnets waste much of the electrical energy as heat, they would have to be physically much larger than superconducting magnets. A landmark for the commercial use of MAGLEV technology occurred in 1990 when it gained the status of a nationally-funded project in Japan. The Minister of Transport authorized construction of the Yamanashi Maglev Test Line which opened on April 3, 1997. In April 2015, the MLX01 test vehicle (shown above) attained an incredible speed of 374 mph (603 kph). Although the technology has now been proven, the wider use of MAGLEV vehicles has been constrained by political and environmental concerns (strong magnetic fields can create a bio-hazard). The world's first MAGLEV train to be adopted into commercial service, a shuttle in Birmingham, England, shut down in 1997 after operating for 11 years. A Sino-German maglev is currently operating over a 30-km course at Pudong International Airport in Shanghai, China. The U.S. plans to put its first (non-superconducting) Maglev train into operation on a Virginia college campus. Click this link for a website that lists other uses for MAGLEV. MRI of a human skull. An area where superconductors can perform a life-saving function is in the field of biomagnetism. Doctors need a non-invasive means of determining what's going on inside the human body. By impinging a strong superconductor-derived magnetic field into the body, hydrogen atoms that exist in the body's water and fat molecules are forced to accept energy from the magnetic field. They then release this energy at a frequency that can be detected and displayed graphically by a computer. Magnetic Resonance Imaging (MRI) was actually discovered in the mid 1940's. But, the first MRI exam on a human being was not performed until July 3, 1977. And, it took almost five hours to produce one image! Today's faster computers process the data in much less time. A tutorial is available on MRI at this link. Or read the latest MRI news at this link. The Korean Superconductivity Group within KRISS has carried biomagnetic technology a step further with the development of a double-relaxation oscillation SQUID (Superconducting QUantum Interference Device) for use in Magnetoencephalography. SQUID's are capable of sensing a change in a magnetic field over a billion times weaker than the force that moves the needle on a compass (compass: 5e-5T, SQUID: e-14T.). With this technology, the body can be probed to certain depths without the need for the strong magnetic fields associated with MRI's. Probably the one event, more than any other, that has been responsible for putting "superconductors" into the American lexicon was the Superconducting Super-Collider project planned for construction in Ellis county, Texas. Though Congress cancelled the multi-billion dollar effort in 1993, the concept of such a large, high-energy collider would never have been viable without superconductors. High-energy particle research hinges on being able to accelerate sub-atomic particles to nearly the speed of light. Superconductor magnets make this possible. CERN, a consortium of several European nations, is doing something similar with its Large Hadron Collider (LHC) recently inaugurated along the Franco-Swiss border. Other related web sites worth visiting include the proton-antiproton collider page at Fermilab. This was the first facility to use superconducting magnets. Get information on the electron-proton collider HERA at the German lab pages of DESY (with English text). And Brookhaven National Laboratory features a page dedicated to its RHIC heavy-ion collider. Electric generators made with superconducting wire are far more efficient than conventional generators wound with copper wire. In fact, their efficiency is above 99% and their size about half that of conventional generators. These facts make them very lucrative ventures for power utilities. General Electric has estimated the potential worldwide market for superconducting generators in the next decade at around $20-30 billion dollars. Late in 2002 GE Power Systems received $12.3 million in funding from the U.S. Department of Energy to move high-temperature superconducting generator technology toward full commercialization. To read the latest news on superconducting generators click Here. Other commercial power projects in the works that employ superconductor technology include energy storage to enhance power stability. American Superconductor Corp. received an order from Alliant Energy in late March 2000 to install a Distributed Superconducting Magnetic Energy Storage System (D-SMES) in Wisconsin. Just one of these 6 D-SMES units has a power reserve of over 3 million watts, which can be retrieved whenever there is a need to stabilize line voltage during a disturbance in the power grid. AMSC has also installed more than 22 of its D-VAR systems to provide instantaneous reactive power support. The General Atomics/Intermagnetics General superconducting Fault Current Controller, employing HTS superconductors. Recently, power utilities have also begun to use superconductor-based transformers and "fault limiters". The Swiss-Swedish company ABB was the first to connect a superconducting transformer to a utility power network in March of 1997. ABB also recently announced the development of a 6.4MVA (mega-volt-ampere) fault current limiter - the most powerful in the world. This new generation of HTS superconducting fault limiters is being called upon due to their ability to respond in just thousandths of a second to limit tens of thousands of amperes of current. Advanced Ceramics Limited is another of several companies that makes BSCCO type fault limiters. Intermagnetics General recently completed tests on its largest (15kv class) power-utility-size fault limiter at a Southern California Edison (SCE) substation near Norwalk, California. And, both the US and Japan have plans to replace underground copper power cables with superconducting BSCCO cable-in-conduit cooled with liquid nitrogen. (See photo below.) By doing this, more current can be routed through existing cable tunnels. In one instance 250 pounds of superconducting wire replaced 18,000 pounds of vintage copper wire, making it over 7000% more space-efficient. An idealized application for superconductors is to employ them in the transmission of commercial power to cities. However, due to the high cost and impracticality of cooling miles of superconducting wire to cryogenic temperatures, this has only happened with short "test runs". In May of 2001 some 150,000 residents of Copenhagen, Denmark, began receiving their electricity through HTS (high-temperature superconducting) material. That cable was only 30 meters long, but proved adequate for testing purposes. In the summer of 2001 Pirelli completed installation of three 400-foot HTS cables for Detroit Edison at the Frisbie Substation capable of delivering 100 million watts of power. This marked the first time commercial power has been delivered to customers of a US power utility through superconducting wire. Intermagnetics General has announced that its IGC-SuperPower subsidiary has joined with BOC and Sumitomo Electric in a $26 million project to install an underground, HTS power cable in Albany, New York, in Niagara Mohawk Power Corporation's power grid. Sumitomo Electric's DI-BSCCO cable was employed in the first in-grid power cable demonstration project sponsored by the U.S. Department of Energy and New York Energy Research & Development Authority. After connecting to the grid successfully on July 2006, the DI-BSCCO cable has been supplying power to approximately 70,000 households without any problems. Currently the longest run of superconductive power cable was made in the AmpaCity project near Essen, Germany, in May 2014. That cable was a kilometer in length. Hypres Superconducting Microchip, Incorporating 6000 Josephson Junctions. The National Science Foundation, along with NASA and DARPA and various universities, are currently researching "petaflop" computers. A petaflop is a thousand-trillion floating point operations per second. Today's fastest computers have only recently reached these speeds. Currently the fastest is the U.S. Department of Energy "Sequoia" Supercomputer, operating at 16.32 petaflops per second. The fastest single processor is a Lenslet optical DSP running at 8 teraflops. It has been conjectured that devices on the order of 50 nanometers in size along with unconventional switching mechanisms, such as the Josephson junctions associated with superconductors, will be necessary to achieve the next level of processing speeds. TRW researchers (now Northrop Grumman) have quantified this further by predicting that 100 billion Josephson junctions on 4000 microprocessors will be necessary to reach 32 petabits per second. These Josephson junctions are incorporated into field-effect transistors which then become part of the logic circuits within the processors. Recently it was demonstrated at the Weizmann Institute in Israel that the tiny magnetic fields that penetrate Type 2 superconductors can be used for storing and retrieving digital information. It is, however, not a foregone conclusion that computers of the future will be built around superconducting devices. Competing technologies, such as quantum (DELTT) transistors, high-density molecule-scale processors , and DNA-based processing also have the potential to achieve petaflop benchmarks. In the electronics industry, ultra-high-performance filters are now being built. Since superconducting wire has near zero resistance, even at high frequencies, many more filter stages can be employed to achive a desired frequency response. This translates into an ability to pass desired frequencies and block undesirable frequencies in high-congestion rf (radio frequency) applications such as cellular telephone systems. ISCO International and Superconductor Technologies are companies currently offering such filters. Superconductors have also found widespread applications in the military. HTSC SQUIDS are being used by the U.S. NAVY to detect mines and submarines. And, significantly smaller motors are being built for NAVY ships using superconducting wire and "tape". In mid-July, 2001, American Superconductor unveiled a 5000-horsepower motor made with superconducting wire (below). An even larger 36.5MW HTS ship propulsion motor was delivered to the U.S. Navy in late 2006 The newest application for HTS wire is in the degaussing of naval vessels. American Superconductor has announced the development of a superconducting degaussing cable. Degaussing of a ship's hull eliminates residual magnetic fields which might otherwise give away a ship's presence. In addition to reduced power requirements, HTS degaussing cable offers reduced size and weight. The military is also looking at using superconductive tape as a means of reducing the length of very low frequency antennas employed on submarines. Normally, the lower the frequency, the longer an antenna must be. However, inserting a coil of wire ahead of the antenna will make it function as if it were much longer. Unfortunately, this loading coil also increases system losses by adding the resistance in the coil's wire. Using superconductive materials can significantly reduce losses in this coil. The Electronic Materials and Devices Research Group at University of Birmingham (UK) is credited with creating the first superconducting microwave antenna. Applications engineers suggest that superconducting carbon nanotubes might be an ideal nano-antenna for high-gigahertz and terahertz frequencies, once a method of achieving zero "on tube" contact resistance is perfected. The most ignominious military use of superconductors may come with the deployment of "E-bombs". These are devices that make use of strong, superconductor-derived magnetic fields to create a fast, high-intensity electro-magnetic pulse (EMP) to disable an enemy's electronic equipment. Such a device saw its first use in wartime in March 2003 when US Forces attacked an Iraqi broadcast facility. Among emerging technologies are a stabilizing momentum wheel (gyroscope) for earth-orbiting satellites that employs the "flux-pinning" properties of imperfect superconductors to reduce friction to near zero. Superconducting x-ray detectors and ultra-fast, superconducting light detectors are being developed due to their inherent ability to detect extremely weak amounts of energy. Already Scientists at the European Space Agency (ESA) have developed what's being called the S-Cam, an optical camera of phenomenal sensitivity (see above photo). And, superconductors may even play a role in Internet communications soon. In late February, 2000, Irvine Sensors Corporation received a $1 million contract to research and develop a superconducting digital router for high-speed data communications up to 160 Ghz. Since Internet traffic is increasing exponentially, superconductor technology may be called upon to meet this super need. Irvine Sensors speculates this router may see use in facilitating Internet2. According to June 2002 estimates by the Conectus consortium, the worldwide market for superconductor products is projected to grow to near US $38 billion by 2020. Low-temperature superconductors are expected to continue to play a dominant role in well-established fields such as MRI and scientific research, with high-temperature superconductors enabling newer applications. The above ISIS graph gives a rough breakdown of the various markets in which superconductors are expected to make a contribution. DIAGRAMATIC REPRESENTATION OF APPLICATION OF SUPERCONDUCTIVITY Legend: Commercial Emerging High Tc Low Tc Various Tcoptions Medical Magnet Resonance Imaging (MRI) MRI Various Nuclear Magnetic Resonance (NMR) NMR (inserts) Industrial MRI, NMR, etc. Magnetic Separation Magnetic Separation Magnetic Shielding Sensors and Transducers Electric Power Power Cables Generators Motors Fault Current Limiters Flywheel Energy Storage Magnetic Energy Storage (SMES) Transformers Fusion Energy Transportation Magnetically levitated trains Marine Propulsion (motors) Marine Propulsion (magnetohydrodynamic) Physics Particle Accelerators Magnets Plasma/Fusion Research Electronics SQUIDs SQUIDs High Speed Computing Quantum Computing Sensors Circuitry Filters CHAPTER FOUR CONCLUSION AND RECOMMENDATION Issues and Recommendations Recent progress in superconductivity follows a pattern that marked previous developments in new materials - for example, in transistors, semiconductors and optical fibers. Materials-based technology development entails high risk and uncertainty compared to more incremental innovations. It typically takes 20 years to move new materials from the laboratory to the commercial arena. Yet products using new materials often yield the most dramatic benefits for society in the long run. The long lead times inherent in HTS technology development necessitates a sustained government role, and government-industry partnerships play a pivotal role in this process. These partnerships require stable and consistent funding and a tolerance for risk. Careful planning is required to ensure parallel progress in related fields, such as cryogenics, to assure broad commercial acceptance of new LTS and of HTS technology. Prospective customers such as electric utilities require a stable and symmetrical climate for investment in research, development and demonstration projects. Conclusion: Superconductors are always amazing in this world. Developed and developing countries of our world are constantly thinking about this super power. Production and transmission of electricity should be improved still more to conserve for future generation. Scientists are working on designing superconductors that can operate at room temperature. The basic equipment and infrastructure already exists to support HTS cryogenic refrigeration systems. To optimize the HTS opportunity, however, there is a continuing need to improve overall system designs with an eye toward commercial operation. The industrial gas industry is well positioned to provide refrigeration in the form of a cooling service. As HTS applications begin to move towards commercial reality, it becomes increasingly necessary to demonstrate cryogenic refrigeration systems that are cost effective and reliable, and that can be serviced and supported by a proven infrastructure. The following areas require specific focus: • Continued support for cryocooler development, such as pulse tube and equivalent technologies, with a focus on reliability and overall life cycle cost reduction. • Demonstration of complete, integrated cryogenic systems that incorporate both the equipment and support infrastructure required for long-term, reliable operation.

seminar on superconductor

SEMINAR ON SUPERCONDUCTIVITY AND ITS APPLICATION ON SCIENCE AND TECHNOLOGY. ABSTRACT: As a consequence, the past decade or two of superconductor discovery can best be summarized by the phrase “expect the unexpected”. Superconductivity is an electrical resistance of exactly zero which occurs in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetismand atomic spectral lines, superconductivity is a quantum mechanical phenomenon. The behavior of superconductor suggests that electron pairs are coupling over a range of hundreds of nanometers, three orders of magnitude larger than the lattice spacing, called cooper pairs. These coupled electrons can take the character of a boson and condense into the ground state. This clear explanation is given by BCS theory. hereby after reading this paper you will easily get the clear ideas of Josephson Devices-BCS theory-applications such as super conducting generators, SEMS, superconducting cables. CHAPTER ONE 1.0 INTRODUCTION A superconductor is a material that can conduct electricity or transport electrons from one atom to another with no resistance. This means no heat, sound or any other form of energy would be released from the material when it has reached "critical temperature" (Tc), or the temperature at which the material becomes superconductive. Unfortunately, most materials must be in an extremely low energy state (very cold) in order to become superconductive. Research is underway to develop compounds that become superconductive at higher temperatures. Currently, an excessive amount of energy must be used in the cooling process making superconductors inefficient and uneconomical. Superconductors come in two different flavors: type I and type II. (1) Type I Superconductors A type I superconductor consists of basic conductive elements that are used in everything from electrical wiring to computer microchips. At present, type I superconductors have Tcs between 0.000325 °K and 7.8 °K at standard pressure. Some type I superconductors require incredible amounts of pressure in order to reach the superconductive state. One such material is sulfur which, requires a pressure of 9.3 million atmospheres (9.4 x 1011 N/m2) and a temperature of 17 °K to reach superconductivity. Some other examples of type I superconductors include Mercury - 4.15 °K, Lead - 7.2 °K, Aluminum - 1.175 °K and Zinc - 0.85 °K. Roughly half of the elements in the periodic table are known to be superconductive. (1) Type II Superconductors A type II superconductor is composed of metallic compounds such as copper or lead. They reach a superconductive state at much higher temperatures when compared to type I superconductors. The cause of this dramatic increase in temperature is not fully understood. The highest Tc reached at stardard pressure, to date, is 135 °K or -138 °C by a compound (HgBa2Ca2Cu3O8) that falls into a group of superconductors known as cuprate perovskites. This group of superconductors generally has a ratio of 2 copper atoms to 3 oxygen atoms, and is considered to be a ceramic. Type II superconductors can also be penetrated by a magnetic field whereas a type I can not 1.2 What is a superconductor? Superconductors are materials that conduct electricity with no resistance. This means that, unlike the more familiar conductors such as copper or steel, a superconductor can carry a current indefinitely without losing any energy. They also have several other very important properties, such as the fact that no magnetic field can exist within a superconductor. Superconductors already have drastically changed the world of medicine with the advent of MRI machines, which have meant a reduction in exploratory surgery. Power utilities, electronics companies, the military, transportation, and theoretical physics have all benefited strongly from the discovery of these materials. A brief history of superconductors The first discovery of a superconductive material took place in 1911 when a Dutch scientist named Heike Kammerlingh Onnes, who was also the first person to liquefy helium, and reached temperatures as low as 1.7 kelvin (K). In the 1960s, two unrelated discoveries made closely together ushered in a new era in which practical superconducting devices were developed and commercialized: one was the discrovery of NbTi superconductor, which provided the first material for the practical manufacture of superconducting wire and shaped components; the second was the Josephson junction, which continues to provide the basis for a variety of unique electronic devices. To this day, the largest successful applications of superconductors remains the powerful electromagnets used in Magnetic Resonance Imaging (MRI) systems (over 22,000MRI magnets made) and research magnets, and the RF accelerator cavities used in high energy physics experiments. Despite the enormous success of NbTi and similar materials, even broader application of superconductors has been restricted by the requirement for cooling to very low temperatures (1.5 - 5K)using liquid helium. In late 1986 J. Georg Bednorz and K. Alexander Müller, two researchers at IBM's Zurich Lab, discovered announced an oxide material that superconducted at 30K. These two researchers were awarded the Nobel Prize in Physics 1987 for their work. Then, in 1987, Paul Chu at the University of Houston discovered YBCO, which became a superconductor at just 90K. Because 90K can be reached using liquid nitrogen, a common industrial refrigerant, these discoveries opened up for the first time the potential for a much wider range of devices. Over the next several months, discoveries of BSCCO and TBCCO brought the transition temperature of superconductors up to 127K. This discovery of these "High Temperature Superconductors" sparked vast interest, and an entire industry dedicated to the research and commercial development of these materials and their applications has emerged. Today, an enormous range of devices are under development for both low and high temperature superconductors. International competition is strong in these materials, and current efforts involve many facets of the electronics, communications, power, medical technology, transportation, military, and materials processing industries. Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. It was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing through a loop of superconducting wire can persist indefinitely with no power source. In 1986, it was discovered that some cuprate-perovskite ceramic materials have a critical temperature above 90 K (−183 °C). Such a high transition temperature is theoretically impossible for a conventional superconductor, leading the materials to be termed high-temperature superconductors. Liquid nitrogen boils at 77 K, and superconduction at higher temperatures than this facilitates many experiments and applications that are less practical at lower temperatures. CHAPTER TWO 2.0 LITERATURE REVIEW This is the first macroscopic theorysuper conductivity observed that mercury to explain the concept of superacts as superconductor below 4.2 k conductivity London proposed that theretemperature. The resistance of his mercury are two types of conduction electronsample did not tend toward some constants namely super electrons, normal electrons.value as the temperature was reduced Here, the super electrons are not subjectedbelow 4.2k. At 4.15k, the DC resistance of to any lattice scattering and they movethe sample is completely vanished. freely over the lattices points. But the total conduction electron density is equal to In 1913, he wrote that no doubt sum of super electrons and normalwas left of the existence of a new state of electrons.mercury in its resistance has practicallyvanished superconducting state. 2. Ginsburg- Landau Theory-1950: The most striking and well known This theory gives the idea that theproperty of superconductor is their lack of super conducting state is characterized byelectrical resistance. In 1933, Meissner and a single complex wave function. ThisOchsen field found, most surprisingly, that theory describes the properties of superwhen a pure metal is cooled through its conducting state such as meissner effect,superconducting transition temperature in zero electrical resistance and Type II superthe presence of magnetic field all magnetic conductor.flux is expelled from within its bulk.Spontaneous exclusion of magnetic flux 3. Bardeen, Cooper and Schriefferfrom a superconductor could not be quite (BCS) theory:complete of course, even in principle This is the first microscopic theorycurrents in metals arises from the flow of based on quantum theory. They introducedelectrons and no physical current sheet can a new pair of electrons called cooper pairbe made indefinitely thin due to repulsion and they are responsible for the superforce between these electrons. Hence the conductivity.temperature at which a normal conductorloses its resistivity and become a Principle:superconductor is known as transitiontemperature (or) critical temperature. This theory states that the electrons experience a special type of attractive At the transition temperature, the interaction, overcoming the coulombfollowing physical changes are observed. forces of repulsion between them, as a result Cooper pairs (i.e.,) electrons pairs 1. The electrical resistance drops to are formed. At low temperature these zero. pair’s moves without scattering (i.e.,) 2. The magnetic flux lines are without any resistance through the lattice excluded from the material. points and the material becomes 3. There is a discontinuous change in superconductor. Here the electrons- lattice- specific heat. electrons interaction should be stronger 4. Further there are also a small than electron-electron interaction. change in thermal conductivity and the volume of the material. The superconducting state of a metal may be considered to be resulting With the help of reference given by from cooperative behavior of conductiononnes, the succeeding scholars proposed electrons. Such a cooperation or coherencethe following theories. 2.1 Classification There are many criteria by which superconductors are classified. The most common are: • Response to a magnetic field: A superconductor can be Type I, meaning it has a single critical field, above which all superconductivity is lost; or Type II, meaning it has two critical fields, between which it allows partial penetration of the magnetic field. • By theory of operation: It is conventional if it can be explained by the BCS theory or its derivatives, or unconventional, otherwise. • By critical temperature: A superconductor is generally considered high temperature if it reaches a superconducting state when cooled using liquid nitrogen – that is, at only Tc > 77 K) – or low temperature if more aggressive cooling techniques are required to reach its critical temperature. • By material: Superconductor material classes include chemical elements (e.g. mercury or lead), alloys (such as niobium-titanium, germanium-niobium, and niobium nitride), ceramics (YBCO and magnesium diboride), or organic superconductors (fullerenes and carbon nanotubes; though perhaps these examples should be included among the chemical elements, as they are composed entirely of carbon). 2.1.1. Elementary properties of superconductors Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature, critical field, and critical current density at which superconductivity is destroyed. On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have exactly zero resistivity to low applied currents when there is no magnetic field present or if the applied field does not exceed a critical value. The existence of these "universal" properties implies that superconductivity is a thermodynamic phase, and thus possesses certain distinguishing properties which are largely independent of microscopic details. 2.1.2. Zero electrical DC resistance Electric cables for accelerators at CERN. Both the massive and slim cables are rated for 12,500 A. Top: conventional cables for LEP; bottom: superconductor-based cables for the LHC The simplest method to measure the electrical resistance of a sample of some material is to place it in an electrical circuit in series with a current source I and measure the resulting voltage V across the sample. The resistance of the sample is given by Ohm's law as R = V / I. If the voltage is zero, this means that the resistance is zero. Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years. Theoretical estimates for the lifetime of a persistent current can exceed the estimated lifetime of the universe, depending on the wire geometry and the temperature.[3] In a normal conductor, an electric current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat, which is essentially the vibrational kinetic energy of the lattice ions. As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance. The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists of bound pairs of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum amount of energy ΔE that must be supplied in order to excite the fluid. Therefore, if ΔE is larger than the thermal energy of the lattice, given by kT, where k is Boltzmann's constant and T is the temperature, the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation. In a class of superconductors known as type II superconductors, including all known high-temperature superconductors, an extremely small amount of resistivity appears at temperatures not too far below the nominal superconducting transition when an electric current is applied in conjunction with a strong magnetic field, which may be caused by the electric current. This is due to the motion of magnetic vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero. 2.2. Superconducting phase transition Behavior of heat capacity (cv, blue) and resistivity (ρ, green) at the superconducting phase transition In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature Tc. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K to less than 1 K. Solid mercury, for example, has a critical temperature of 4.2 K. As of 2009, the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB2),[7][8] although this material displays enough exotic properties that there is some doubt about classifying it as a "conventional" superconductor.[9] Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown. Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high critical temperature. Similarly, at a fixed temperature below the critical temperature, superconducting materials cease to superconduct when an external magnetic field is applied which is greater than the critical magnetic field. This is because the Gibbs free energy of the superconducting phase increases quadratically with the magnetic field while the free energy of the normal phase is roughly independent of the magnetic field. If the material superconducts in the absence of a field, then the superconducting phase free energy is lower than that of the normal phase and so for some finite value of the magnetic field (proportional to the square root of the difference of the free energies at zero magnetic field) the two free energies will be equal and a phase transition to the normal phase will occur. More generally, a higher temperature and a stronger magnetic field lead to a smaller fraction of the electrons in the superconducting band and consequently a longer London penetration depth of external magnetic fields and currents. The penetration depth becomes infinite at the phase transition. The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as e−α/T for some constant, α. This exponential behavior is one of the pieces of evidence for the existence of the energy gap. The order of the superconducting phase transition was long a matter of debate. Experiments indicate that the transition is second-order, meaning there is no latent heat. However in the presence of an external magnetic field there is latent heat, because the superconducting phase has a lower entropy below the critical temperature than the normal phase. It has been experimentally demonstrated[10] that, as a consequence, when the magnetic field is increased beyond the critical field, the resulting phase transition leads to a decrease in the temperature of the superconducting material. Calculations in the 1970s suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field. In the 1980s it was shown theoretically with the help of a disorder field theory, in which the vortex lines of the superconductor play a major role, that the transition is of second order within the type II regime and of first order (i.e., latent heat) within the type I regime, and that the two regions are separated by a tricritical point.[11] The results were strongly supported by Monte Carlo computer simulations.[12] 2.2.1 Meissner effect When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected. The Meissner effect does not cause the field to be completely ejected but instead the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material. The Meissner effect is a defining characteristic of superconductivity. For most superconductors, the London penetration depth is on the order of 100 nm. The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenz's law, when a changing magnetic field is applied to a conductor, it will induce an electric current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from this—it is the spontaneous expulsion which occurs during transition to superconductivity. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law. The Meissner effect was given a phenomenological explanation by the brothers Fritz and Heinz London, who showed that the electromagnetic free energy in a superconductor is minimized provided where H is the magnetic field and λ is the London penetration depth. This equation, which is known as the London equation, predicts that the magnetic field in a superconductor decays exponentially from whatever value it possesses at the surface. A superconductor with little or no magnetic field within it is said to be in the Meissner state. The Meissner state breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value Hc. Depending on the geometry of the sample, one may obtain an intermediate state[13] consisting of a baroque pattern[14] of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value Hc1 leads to a mixed state (also known as the vortex state) in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electric current as long as the current is not too large. At a second critical field strength Hc2, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called fluxons because the flux carried by these vortices is quantized. Most pure elemental superconductors, except niobium and carbon nanotubes, are Type I, while almost all impure and compound superconductors are Type II. 2.2.2. London moment Conversely, a spinning superconductor generates a magnetic field, precisely aligned with the spin axis. The effect, the London moment, was put to good use in Gravity Probe B. This experiment measured the magnetic fields of four superconducting gyroscopes to determine their spin axes. This was critical to the experiment since it is one of the few ways to accurately determine the spin axis of an otherwise featureless sphere. 2.3. History of superconductivity Superconductivity was discovered on April 8, 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently produced liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared. In the same experiment, he also observed the superfluid transition of helium at 2.2 K, without recognizing its significance. The precise date and circumstances of the discovery were only reconstructed a century later, when Onnes's notebook was found.[16] In subsequent decades, superconductivity was observed in several other materials. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. Great efforts have been devoted to finding out how and why superconductivity works; the important step occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect.[17] In 1935, Fritz and Heinz London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current.[18] 2.3.1. London theory The first phenomenological theory of superconductivity was London theory. It was put forward by the brothers Fritz and Heinz London in 1935, shortly after the discovery that magnetic fields are expelled from superconductors. A major triumph of the equations of this theory is their ability to explain the Meissner effect,[19] wherein a material exponentially expels all internal magnetic fields as it crosses the superconducting threshold. By using the London equation, one can obtain the dependence of the magnetic field inside the superconductor on the distance to the surface.[20] There are two London equations: The first equation follows from Newton's second law for superconducting electrons. 2.3.2. Conventional theories (1950s) During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957).[21][22] In 1950, the phenomenological Ginzburg-Landau theory of superconductivity was devised by Landau and Ginzburg.[23] This theory, which combined Landau's theory of second-order phase transitions with a Schrödinger-like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Abrikosov showed that Ginzburg-Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau had received the 1962 Nobel Prize for other work, and died in 1968). The four-dimensional extension of the Ginzburg-Landau theory, the Coleman-Weinberg model, is important in quantum field theory and cosmology. Also in 1950, Maxwell and Reynolds et al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element.[24][25] This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity. The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper and Schrieffer.[22] This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. The BCS theory was set on a firmer footing in 1958, when N. N. Bogolyubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian.[26] In 1959, Lev Gor'kov showed that the BCS theory reduced to the Ginzburg-Landau theory close to the critical temperature.[27][28] Generalizations of BCS theory for conventional superconductors form the basis for understanding of the phenomenon of superfluidity, because they fall into the lambda transition universality class. The extent to which such generalizations can be applied to unconventional superconductors is still controversial. 2.4. Further history The first practical application of superconductivity was developed in 1954 with Dudley Allen Buck's invention of the cryotron.[29] Two superconductors with greatly different values of critical magnetic field are combined to produce a fast, simple, switch for computer elements. Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated. Much later, in 1955, G.B. Yntema [30] succeeded in constructing a small 0.7-tesla iron-core electromagnet with superconducting niobium wire windings. Then, in 1961, J.E. Kunzler, E. Buehler, F.S.L. Hsu, and J.H. Wernick [31] made the startling discovery that, at 4.2 degrees kelvin, a compound consisting of three parts niobium and one part tin, was capable of supporting a current density of more than 100,000 amperes per square centimeter in a magnetic field of 8.8 tesla. Despite being brittle and difficult to fabricate, niobium-tin has since proved extremely useful in supermagnets generating magnetic fields as high as 20 tesla. In 1962 T.G. Berlincourt and R.R. Hake [32][33] discovered that alloys of niobium and titanium are suitable for applications up to 10 tesla. Promptly thereafter, commercial production of niobium-titanium supermagnet wire commenced at Westinghouse Electric Corporation and at Wah Chang Corporation. Although niobium-titanium boasts less-impressive superconductng properties than those of niobium-tin, niobium-titanium has, nevertheless, become the most widely-used “workhorse” supermagnet material, in large measure a consequence of its very-high ductility and ease of fabrication. However, both niobium-tin and niobium-titanium find wide application in MRI medical imagers, bending and focusing magnets for enormous high-energy-particle accelerators, and a host of other applications. Conectus, a European superconductivity consortium, estimated that In 2014, global economic activity, for which superconductivity was indispensable, amounted to about five billion euros, with MRI systems accounting for about 80% of that total. In 1962, Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator.[34] This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. It is used in the most accurate available measurements of the magnetic flux quantum Φ0 = h/(2e), where h is the Planck constant. Coupled with the quantum Hall resistivity, this leads to a precise measurement of the Planck constant. Josephson was awarded the Nobel Prize for this work in 1973. In 2008, it was proposed that the same mechanism that produces superconductivity could produce a superinsulator state in some materials, with almost infinite electrical resistance. CHAPTER THREE 3.0. High-temperature superconductivity Timeline of superconducting materials Main article: High-temperature superconductivity Until 1986, physicists had believed that BCS theory forbade superconductivity at temperatures above about 30 K. In that year, Bednorz and Müller discovered superconductivity in a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987).[6] It was soon found that replacing the lanthanum with yttrium (i.e., making YBCO) raised the critical temperature to 92 K.[36] This temperature jump is particularly significant, since it allows liquid nitrogen as a refrigerant, replacing liquid helium.[36] This can be important commercially because liquid nitrogen can be produced relatively cheaply, even on-site, avoiding some of the problems (such as so-called "solid air" plugs[clarification needed]) which arise when liquid helium is used in piping.[37][38] Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics. There are currently two main hypotheses – the resonating-valence-bond theory, and spin fluctuation which has the most support in the research community.[40] The second hypothesis proposed that electron pairing in high-temperature superconductors is mediated by short-range spin waves known as paramagnons. Since about 1993, the highest temperature superconductor was a ceramic material consisting of mercury, barium, calcium, copper and oxygen (HgBa2Ca2Cu3O8+δ) with Tc = 133–138 K.[43][44] The latter experiment (138 K) still awaits experimental confirmation, however. In February 2008, an iron-based family of high-temperature superconductors was discovered. Hideo Hosono, of the Tokyo Institute of Technology, and colleagues found lanthanum oxygen fluorine iron arsenide (LaO1-xFxFeAs), an oxypnictide that superconducts below 26 K. Replacing the lanthanum in LaO1−xFxFeAs with samarium leads to superconductors that work at 55 K. Fundamental Properties of Superconductors A superconducting or superfluid phase is considered a different thermodynamical phase when compared to the normal state that exists when the temperature T>T_c, where T_c means the critical temperature below which the superconducting or superfuid state appears. For example, liquid 4He under its vapor pressure becomes superfluid at T_c=2.17 K. So, the passage from one state to the other is called a phase transition, and it is accompanied by a strong increase of the specifi heat when the temperature is near T_c, with a strong release of entropy. This phenomena, experimentally seen, leads to the formation of a more ordered state of matter (see also precedent video). Fundamentally, a superconductor is a conductor that has undergone a phase transition to a lower energy state below the critical temperature T_c, characterized by the appearance of groups of paired electrons, the so called Cooper pairs, carrying electrical current without any resistance and responsible, among other properties, of perfect diamagnetism. We may distinguish two types of superconductors. A Type I supercondcutor, is characterized by the following properties [1]: • zero electrical resistance and perfect diamagnetism at a temperature below T_c. Normally, at temperatures above T_c this material is a normal metal, although not a very good conductor; • perfect diamagnetism, also called Meissner effect, the magnetic field stays outside the material, cann’t penetrate the material. Curiosly enough, if you appply an external magnetic field B_app above a given critial magnetic field, B_c, the material suffers a transition from superconductor to normal state. An approximate functional dependence on temperature for this critical magnetic field is given by And what is the diamagnetic property of matter? This property is a kind of negative magnetism. This effect was studied in the framework of classical mechanical by Paul Langevin in 1905 [2], using previous and revolutionary ideas proposed formerly by André-Marie Ampère[3] and Wilhelm Weber [4] (nowadays we barely talk about these two great men of science that really use their minds for the advancement of science and the progress of mankind…). Langevin found, in the classic framework provided by Ampère and Weber, that N electrons moving in orbits around the nucleus at an average distance , such that the (constant and negative) magnetic susceptibility χ is given by The magnetic susceptibility is the ratio of M/H, where M is the magnetization field and H the magnetic field. The susceptibility χ is slightly negative for diamagnets, but acquires small positive values for paramagnetic substances (e.g., ), and is strongly positive for ferromagnetics substances (e.g., Fe). It can be shown that a material constitute of paramagnetic ions with magnetic moment μ, obeys the Curie-Weiss law: where n means the concentration of paramagnetic ions, Θ is the Curie-Weiss constant () . when perfect diamagnetism is achieved, χ=-1, that is, the magnetization M is directed opposite to the H field, cancelling it, M=-H. For example, when a superconductor with spherical form is placed nearby the poles of a magnet, it results a superposition of the applied magnetic field B_app, and the resulting dipole field, giving a curvature of the magnetic field lines of the form. The dipole result when a uniform permanent magnetization M is parallel to the axis Oz (see Section 5.10 in the textbook of J. D. Jackson [4]). Besides perfect diamagnetism, the other important property of the superconducting state is its zero resistance. In ideal conditions, an electric current established in a loop of supercuncting wire will last indefenitely. The surface resistance of the material with a current flowing along a film of thickness d, must satisfy the condition where ρ is the electric resistivity, h is the Planck constant and e is the absolute charge of the electron. Applications Of superconductivity Superconductors are already used in many fields: electricity, medical applications, electronics and even trains. They are used in laboratories, especially in particle accelerators, in astrophysics with the use of bolometers, in ultrasensitive magnetic detectors called SQUIDs, and in superconducting coils to produce very strong magnetic fields. However, they need to be cooled to very low temperatures, which restricts their use in our everyday life. But new applications are already operational in laboratories and will be able to spread to our cities and our homes if the cooling process becomes less expensive or, better, if we discover superconducting materials that do not require any cooling. If this happens, we can expect an actual revolution in energies and environment on the one side, and transportation and computer science on the other. Technological applications of superconductivity Superconducting magnets are some of the most powerful electromagnets known. They are used in MRI/NMR machines, mass spectrometers, and the beam-steering magnets used in particle accelerators. They can also be used for magnetic separation, where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries. In the 1950s and 1960s, superconductors were used to build experimental digital computers using cryotron switches. More recently, superconductors have been used to make digital circuits based on rapid single flux quantum technology and RF and microwave filters for mobile phone base stations. Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. SQUIDs are used in scanning SQUID microscopes and magnetoencephalography. Series of Josephson devices are used to realize the SI volt. Depending on the particular mode of operation, a superconductor-insulator-superconductor Josephson junction can be used as a photon detector or as a mixer. The large resistance change at the transition from the normal- to the superconducting state is used to build thermometers in cryogenic micro-calorimeter photon detectors. The same effect is used in ultrasensitive bolometers made from superconducting materials. Other early markets are arising where the relative efficiency, size and weight advantages of devices based on high-temperature superconductivity outweigh the additional costs involved. Promising future applications include high-performance smart grid, electric power transmission, transformers, power storage devices, electric motors (e.g. for vehicle propulsion, as in vactrains or maglev trains), magnetic levitation devices, fault current limiters, enhancing spintronic devices with superconducting materials,[48] and superconducting magnetic refrigeration. However, superconductivity is sensitive to moving magnetic fields so applications that use alternating current (e.g. transformers) will be more difficult to develop than those that rely upon direct current. Some of the technological applications of superconductivity include: • the production of sensitive magnetometers based on SQUIDs • fast digital circuits (including those based on Josephson junctions and rapid single flux quantum technology), • powerful superconducting electromagnets used in maglev trains, Magnetic Resonance Imaging (MRI) and Nuclear magnetic resonance (NMR) machines, magnetic confinement fusion reactors (e.g. tokamaks), and the beam-steering and focusing magnets used in particle accelerators • low-loss power cables • RF and microwave filters (e.g., for mobile phone base stations, as well as military ultra-sensitive/selective receivers) • fast fault current limiters • high sensitivity particle detectors, including the transition edge sensor, the superconducting bolometer, the superconducting tunnel junction detector, the kinetic inductance detector, and the superconducting nanowire single-photon detector • railgun and coilgun magnets • electric motors and generators[1] Contents • 1 Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) • 2 High-temperature superconductivity (HTS) o 2.1 HTS-based systems o 2.2 Holbrook Superconductor Project o 2.3 Tres Amigas Project o 2.4 Magnesium diboride • 3 Notes Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) The biggest application for superconductivity is in producing the large volume, stable, and high magnetic fields required for MRI and NMR. This represents a multi-billion US$ market for companies such as Oxford Instruments and Siemens. The magnets typically use low temperature superconductors (LTS) because high-temperature superconductors are not yet cheap enough to cost-effectively deliver the high, stable and large volume fields required, notwithstanding the need to cool LTS instruments to liquid helium temperatures. Superconductors are also used in high field scientific magnets. High-temperature superconductivity (HTS) The commercial applications so far for high temperature superconductors (HTS) have been limited. HTS can superconduct at temperatures above the boiling point of liquid nitrogen, which makes them cheaper to cool than low temperature superconductors (LTS). However, the problem with HTS technology is that the currently known high temperature superconductors are brittle ceramics which are expensive to manufacture and not easily formed into wires or other useful shapes.[2] Therefore the applications for HTS have been where it has some other intrinsic advantage, e.g. in • low thermal loss current leads for LTS devices (low thermal conductivity), • RF and microwave filters (low resistance to RF), and • increasingly in specialist scientific magnets, particularly where size and electricity consumption are critical (while HTS wire is much more expensive than LTS in these applications, this can be offset by the relative cost and convenience of cooling); the ability to ramp field is desired (the higher and wider range of HTS's operating temperature means faster changes in field can be managed); or cryogen free operation is desired (LTS generally requires liquid helium that is becoming more scarce and expensive). HTS-based systems HTS has application in scientific and industrial magnets, including use in NMR and MRI systems. Commercial systems are now available in each category.[3] Also one intrinsic attribute of HTS is that it can withstand much higher magnetic fields than LTS, so HTS at liquid helium temperatures are being explored for very high-field inserts inside LTS magnets. Promising future industrial and commercial HTS applications include Induction heaters, transformers, fault current limiters, power storage, motors and generators, fusion reactors (see ITER) and magnetic levitation devices. Early applications will be where the benefit of smaller size, lower weight or the ability to rapidly switch current (fault current limiters) outweighs the added cost. Longer-term as conductor price falls HTS systems should be competitive in a much wider range of applications on energy efficiency grounds alone. (For a relatively technical and US-centric view of state of play of HTS technology in power systems and the development status of Generation 2 conductor see Superconductivity for Electric Systems 2008 US DOE Annual Peer Review.) Holbrook Superconductor Project The Holbrook Superconductor Project is a project to design and build the world's first production superconducting transmission power cable. The cable was commissioned in late June 2008. The suburban Long Island electrical substation is fed by about 600-meter-long underground cable system consists of about 99 miles of high-temperature superconductor wire manufactured by American Superconductor, installed underground and chilled with liquid nitrogen greatly reducing the costly right-of-way required to deliver additional power.[4] Tres Amigas Project American Superconductor was chosen for The Tres Amigas Project, the United States’ first renewable energy market hub.[5] The Tres Amigas renewable energy market hub will be a multi-mile, triangular electricity pathway of superconductor electricity pipelines capable of transferring and balancing many gigawatts of power between three U.S. power grids (the Eastern Interconnection, the Western Interconnection and the Texas Interconnection). Unlike traditional powerlines, it will transfer power as DC instead of AC current. It will be located in Clovis, New Mexico. Magnesium diboride Magnesium diboride is a much cheaper superconductor than either BSCCO or YBCO in terms of cost per current-carrying capacity per length (cost/(kA*m)), in the same ballpark as LTS, and on this basis many manufactured wires are already cheaper than copper. Furthermore, MgB2 superconducts at temperatures higher than LTS (its critical temperature is 39 K, compared with less than 10 K for NbTi and 18.3 K for Nb3Sn), introducing the possibility of using it at 10-20 K in cryogen-free magnets or perhaps eventually in liquid hydrogen.[citation needed] However MgB2 is limited in the magnetic field it can tolerate at these higher temperatures, so further research is required to demonstrate its competitiveness in higher field applications. Transportation. The rapid and efficient movement of people and goods, by land and by sea, poses important logistical, environmental, land use and other challenges. Superconductors are enabling a new generation of transport technologies including ship propulsion systems, magnetically levitated trains, and railway traction transformers. Medicine. Advances in HTS promise more compact and less costly Magnetic Resonance Imaging (MRI) systems with superior imaging capabilities. In addition, Magneto-Encephalography (MEG), Magnetic Source Imaging (MSI) and Magneto-Cardiology (MCG) enable non-invasive diagnosis of brain and heart functionality. Industry. Large motors rated at 1000 HP and above consume 25% of all electricity generated in the United States. They offer a prime target for the use of HTS in substantially reducing electrical losses. Powerful magnets for water remediation, materials purification, and industrial processing are also in the demonstration stages. Communications. Over the past decade, HTS filters have come into widespread use in cellular communications systems. They enhance signal-to-noise ratios, enabling reliable service with fewer, more widely-spaced cell towers. As the world moves from analog to all digital communications, LTS chips offer dramatic performance improvements in many commercial and military applications. Scientific Research. Using superconducting materials, today’s leading-edge scientific research facilities are pushing the frontiers of human knowledge - and pursuing breakthroughs that could lead to new techniques ranging from the clean, abundant energy from nuclear fusion to computing at speeds much faster than the theoretical limit of silicon technology. Commercial Application of Superconductors Superconductivity: Applications in Electric Power Today’s power grid operators face complex challenges that threaten their ability to provide reliable service: steady demand growth; aging infrastructure; mounting obstacles to siting new plants and lines; and new uncertainties brought on by structural and regulatory reforms. Advances in high temperature superconductivity (HTS) over the past two decades are yielding a new set of technology tools to renew this critical infrastructure, and to enhance the capacity, reliability and efficiency, of the nation’s power system. The US Power Grid Under Stress Power industry experts in the United States are widely agreed that today’s aging power grid must be strengthened and modernized. Utilities must cope with a growth in the underlying level of demand driven by our expanding, high technology-intensive economy. Consumers in the digital age have rising expectations and requirements for grid reliability and power quality. Competitive reforms have brought about new patterns of power flows. EPRI (the Electric Power Research Institute) has estimated that $100 billion must be spent over the next ten years to achieve and maintain acceptable levels of electric reliability. Uses for Superconductors Magnetic-levitation is an application where superconductors perform extremely well. Transport vehicles such as trains can be made to "float" on strong superconducting magnets, virtually eliminating friction between the train and its tracks. Not only would conventional electromagnets waste much of the electrical energy as heat, they would have to be physically much larger than superconducting magnets. A landmark for the commercial use of MAGLEV technology occurred in 1990 when it gained the status of a nationally-funded project in Japan. The Minister of Transport authorized construction of the Yamanashi Maglev Test Line which opened on April 3, 1997. In April 2015, the MLX01 test vehicle (shown above) attained an incredible speed of 374 mph (603 kph). Although the technology has now been proven, the wider use of MAGLEV vehicles has been constrained by political and environmental concerns (strong magnetic fields can create a bio-hazard). The world's first MAGLEV train to be adopted into commercial service, a shuttle in Birmingham, England, shut down in 1997 after operating for 11 years. A Sino-German maglev is currently operating over a 30-km course at Pudong International Airport in Shanghai, China. The U.S. plans to put its first (non-superconducting) Maglev train into operation on a Virginia college campus. Click this link for a website that lists other uses for MAGLEV. MRI of a human skull. An area where superconductors can perform a life-saving function is in the field of biomagnetism. Doctors need a non-invasive means of determining what's going on inside the human body. By impinging a strong superconductor-derived magnetic field into the body, hydrogen atoms that exist in the body's water and fat molecules are forced to accept energy from the magnetic field. They then release this energy at a frequency that can be detected and displayed graphically by a computer. Magnetic Resonance Imaging (MRI) was actually discovered in the mid 1940's. But, the first MRI exam on a human being was not performed until July 3, 1977. And, it took almost five hours to produce one image! Today's faster computers process the data in much less time. A tutorial is available on MRI at this link. Or read the latest MRI news at this link. The Korean Superconductivity Group within KRISS has carried biomagnetic technology a step further with the development of a double-relaxation oscillation SQUID (Superconducting QUantum Interference Device) for use in Magnetoencephalography. SQUID's are capable of sensing a change in a magnetic field over a billion times weaker than the force that moves the needle on a compass (compass: 5e-5T, SQUID: e-14T.). With this technology, the body can be probed to certain depths without the need for the strong magnetic fields associated with MRI's. Probably the one event, more than any other, that has been responsible for putting "superconductors" into the American lexicon was the Superconducting Super-Collider project planned for construction in Ellis county, Texas. Though Congress cancelled the multi-billion dollar effort in 1993, the concept of such a large, high-energy collider would never have been viable without superconductors. High-energy particle research hinges on being able to accelerate sub-atomic particles to nearly the speed of light. Superconductor magnets make this possible. CERN, a consortium of several European nations, is doing something similar with its Large Hadron Collider (LHC) recently inaugurated along the Franco-Swiss border. Other related web sites worth visiting include the proton-antiproton collider page at Fermilab. This was the first facility to use superconducting magnets. Get information on the electron-proton collider HERA at the German lab pages of DESY (with English text). And Brookhaven National Laboratory features a page dedicated to its RHIC heavy-ion collider. Electric generators made with superconducting wire are far more efficient than conventional generators wound with copper wire. In fact, their efficiency is above 99% and their size about half that of conventional generators. These facts make them very lucrative ventures for power utilities. General Electric has estimated the potential worldwide market for superconducting generators in the next decade at around $20-30 billion dollars. Late in 2002 GE Power Systems received $12.3 million in funding from the U.S. Department of Energy to move high-temperature superconducting generator technology toward full commercialization. To read the latest news on superconducting generators click Here. Other commercial power projects in the works that employ superconductor technology include energy storage to enhance power stability. American Superconductor Corp. received an order from Alliant Energy in late March 2000 to install a Distributed Superconducting Magnetic Energy Storage System (D-SMES) in Wisconsin. Just one of these 6 D-SMES units has a power reserve of over 3 million watts, which can be retrieved whenever there is a need to stabilize line voltage during a disturbance in the power grid. AMSC has also installed more than 22 of its D-VAR systems to provide instantaneous reactive power support. The General Atomics/Intermagnetics General superconducting Fault Current Controller, employing HTS superconductors. Recently, power utilities have also begun to use superconductor-based transformers and "fault limiters". The Swiss-Swedish company ABB was the first to connect a superconducting transformer to a utility power network in March of 1997. ABB also recently announced the development of a 6.4MVA (mega-volt-ampere) fault current limiter - the most powerful in the world. This new generation of HTS superconducting fault limiters is being called upon due to their ability to respond in just thousandths of a second to limit tens of thousands of amperes of current. Advanced Ceramics Limited is another of several companies that makes BSCCO type fault limiters. Intermagnetics General recently completed tests on its largest (15kv class) power-utility-size fault limiter at a Southern California Edison (SCE) substation near Norwalk, California. And, both the US and Japan have plans to replace underground copper power cables with superconducting BSCCO cable-in-conduit cooled with liquid nitrogen. (See photo below.) By doing this, more current can be routed through existing cable tunnels. In one instance 250 pounds of superconducting wire replaced 18,000 pounds of vintage copper wire, making it over 7000% more space-efficient. An idealized application for superconductors is to employ them in the transmission of commercial power to cities. However, due to the high cost and impracticality of cooling miles of superconducting wire to cryogenic temperatures, this has only happened with short "test runs". In May of 2001 some 150,000 residents of Copenhagen, Denmark, began receiving their electricity through HTS (high-temperature superconducting) material. That cable was only 30 meters long, but proved adequate for testing purposes. In the summer of 2001 Pirelli completed installation of three 400-foot HTS cables for Detroit Edison at the Frisbie Substation capable of delivering 100 million watts of power. This marked the first time commercial power has been delivered to customers of a US power utility through superconducting wire. Intermagnetics General has announced that its IGC-SuperPower subsidiary has joined with BOC and Sumitomo Electric in a $26 million project to install an underground, HTS power cable in Albany, New York, in Niagara Mohawk Power Corporation's power grid. Sumitomo Electric's DI-BSCCO cable was employed in the first in-grid power cable demonstration project sponsored by the U.S. Department of Energy and New York Energy Research & Development Authority. After connecting to the grid successfully on July 2006, the DI-BSCCO cable has been supplying power to approximately 70,000 households without any problems. Currently the longest run of superconductive power cable was made in the AmpaCity project near Essen, Germany, in May 2014. That cable was a kilometer in length. Hypres Superconducting Microchip, Incorporating 6000 Josephson Junctions. The National Science Foundation, along with NASA and DARPA and various universities, are currently researching "petaflop" computers. A petaflop is a thousand-trillion floating point operations per second. Today's fastest computers have only recently reached these speeds. Currently the fastest is the U.S. Department of Energy "Sequoia" Supercomputer, operating at 16.32 petaflops per second. The fastest single processor is a Lenslet optical DSP running at 8 teraflops. It has been conjectured that devices on the order of 50 nanometers in size along with unconventional switching mechanisms, such as the Josephson junctions associated with superconductors, will be necessary to achieve the next level of processing speeds. TRW researchers (now Northrop Grumman) have quantified this further by predicting that 100 billion Josephson junctions on 4000 microprocessors will be necessary to reach 32 petabits per second. These Josephson junctions are incorporated into field-effect transistors which then become part of the logic circuits within the processors. Recently it was demonstrated at the Weizmann Institute in Israel that the tiny magnetic fields that penetrate Type 2 superconductors can be used for storing and retrieving digital information. It is, however, not a foregone conclusion that computers of the future will be built around superconducting devices. Competing technologies, such as quantum (DELTT) transistors, high-density molecule-scale processors , and DNA-based processing also have the potential to achieve petaflop benchmarks. In the electronics industry, ultra-high-performance filters are now being built. Since superconducting wire has near zero resistance, even at high frequencies, many more filter stages can be employed to achive a desired frequency response. This translates into an ability to pass desired frequencies and block undesirable frequencies in high-congestion rf (radio frequency) applications such as cellular telephone systems. ISCO International and Superconductor Technologies are companies currently offering such filters. Superconductors have also found widespread applications in the military. HTSC SQUIDS are being used by the U.S. NAVY to detect mines and submarines. And, significantly smaller motors are being built for NAVY ships using superconducting wire and "tape". In mid-July, 2001, American Superconductor unveiled a 5000-horsepower motor made with superconducting wire (below). An even larger 36.5MW HTS ship propulsion motor was delivered to the U.S. Navy in late 2006 The newest application for HTS wire is in the degaussing of naval vessels. American Superconductor has announced the development of a superconducting degaussing cable. Degaussing of a ship's hull eliminates residual magnetic fields which might otherwise give away a ship's presence. In addition to reduced power requirements, HTS degaussing cable offers reduced size and weight. The military is also looking at using superconductive tape as a means of reducing the length of very low frequency antennas employed on submarines. Normally, the lower the frequency, the longer an antenna must be. However, inserting a coil of wire ahead of the antenna will make it function as if it were much longer. Unfortunately, this loading coil also increases system losses by adding the resistance in the coil's wire. Using superconductive materials can significantly reduce losses in this coil. The Electronic Materials and Devices Research Group at University of Birmingham (UK) is credited with creating the first superconducting microwave antenna. Applications engineers suggest that superconducting carbon nanotubes might be an ideal nano-antenna for high-gigahertz and terahertz frequencies, once a method of achieving zero "on tube" contact resistance is perfected. The most ignominious military use of superconductors may come with the deployment of "E-bombs". These are devices that make use of strong, superconductor-derived magnetic fields to create a fast, high-intensity electro-magnetic pulse (EMP) to disable an enemy's electronic equipment. Such a device saw its first use in wartime in March 2003 when US Forces attacked an Iraqi broadcast facility. Among emerging technologies are a stabilizing momentum wheel (gyroscope) for earth-orbiting satellites that employs the "flux-pinning" properties of imperfect superconductors to reduce friction to near zero. Superconducting x-ray detectors and ultra-fast, superconducting light detectors are being developed due to their inherent ability to detect extremely weak amounts of energy. Already Scientists at the European Space Agency (ESA) have developed what's being called the S-Cam, an optical camera of phenomenal sensitivity (see above photo). And, superconductors may even play a role in Internet communications soon. In late February, 2000, Irvine Sensors Corporation received a $1 million contract to research and develop a superconducting digital router for high-speed data communications up to 160 Ghz. Since Internet traffic is increasing exponentially, superconductor technology may be called upon to meet this super need. Irvine Sensors speculates this router may see use in facilitating Internet2. According to June 2002 estimates by the Conectus consortium, the worldwide market for superconductor products is projected to grow to near US $38 billion by 2020. Low-temperature superconductors are expected to continue to play a dominant role in well-established fields such as MRI and scientific research, with high-temperature superconductors enabling newer applications. The above ISIS graph gives a rough breakdown of the various markets in which superconductors are expected to make a contribution. DIAGRAMATIC REPRESENTATION OF APPLICATION OF SUPERCONDUCTIVITY Legend: Commercial Emerging High Tc Low Tc Various Tcoptions Medical Magnet Resonance Imaging (MRI) MRI Various Nuclear Magnetic Resonance (NMR) NMR (inserts) Industrial MRI, NMR, etc. Magnetic Separation Magnetic Separation Magnetic Shielding Sensors and Transducers Electric Power Power Cables Generators Motors Fault Current Limiters Flywheel Energy Storage Magnetic Energy Storage (SMES) Transformers Fusion Energy Transportation Magnetically levitated trains Marine Propulsion (motors) Marine Propulsion (magnetohydrodynamic) Physics Particle Accelerators Magnets Plasma/Fusion Research Electronics SQUIDs SQUIDs High Speed Computing Quantum Computing Sensors Circuitry Filters CHAPTER FOUR CONCLUSION AND RECOMMENDATION Issues and Recommendations Recent progress in superconductivity follows a pattern that marked previous developments in new materials - for example, in transistors, semiconductors and optical fibers. Materials-based technology development entails high risk and uncertainty compared to more incremental innovations. It typically takes 20 years to move new materials from the laboratory to the commercial arena. Yet products using new materials often yield the most dramatic benefits for society in the long run. The long lead times inherent in HTS technology development necessitates a sustained government role, and government-industry partnerships play a pivotal role in this process. These partnerships require stable and consistent funding and a tolerance for risk. Careful planning is required to ensure parallel progress in related fields, such as cryogenics, to assure broad commercial acceptance of new LTS and of HTS technology. Prospective customers such as electric utilities require a stable and symmetrical climate for investment in research, development and demonstration projects. Conclusion: Superconductors are always amazing in this world. Developed and developing countries of our world are constantly thinking about this super power. Production and transmission of electricity should be improved still more to conserve for future generation. Scientists are working on designing superconductors that can operate at room temperature. The basic equipment and infrastructure already exists to support HTS cryogenic refrigeration systems. To optimize the HTS opportunity, however, there is a continuing need to improve overall system designs with an eye toward commercial operation. The industrial gas industry is well positioned to provide refrigeration in the form of a cooling service. As HTS applications begin to move towards commercial reality, it becomes increasingly necessary to demonstrate cryogenic refrigeration systems that are cost effective and reliable, and that can be serviced and supported by a proven infrastructure. The following areas require specific focus: • Continued support for cryocooler development, such as pulse tube and equivalent technologies, with a focus on reliability and overall life cycle cost reduction. • Demonstration of complete, integrated cryogenic systems that incorporate both the equipment and support infrastructure required for long-term, reliable operation.