MALAVIYA NATIONAL INSTITUTE OFTECHNOLOGY

SUPERCONDUCTOR

BySunil Kumar Meena

2008UEE153

Under the guidance ofMrs.NikitaJhajharia

Department of Electrical Engineering

MNIT Jaipur

ACKNOWLEDGMENT

Any mission can never conclude without cooperation from sur-roundings. It is a great pleasure for me to make use of thisopportunity to express my thanks to those persons who helpedme to bring out my presentation as a successful venture.

First of all I express my deep sense of gratitude & sincerethanks to my mentor Nikita Jhajharia for encouraging me todeliver my seminar in the topic of my interest & also giving methe constant and valuable guidance, in absence of which my pre-sentation would have been incomplete.

Last but not the least, I thank all of my colleagues and friendsfor assisting me and helping me.

Sunil Kumar Meena2008UEE153Third YearElectrical Engineering

Contents

1 INTRODUCTION 3

2 Applications of Superconductivity 82.1 Superconducting Magnets . . . . . . . . . . . . . . . . . . . . 82.2 Power Transmission . . . . . . . . . . . . . . . . . . . . . . . . 102.3 Transportation (Maglev Trains) . . . . . . . . . . . . . . . . . 112.4 Electric Motors . . . . . . . . . . . . . . . . . . . . . . . . . . 132.5 Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.6 Military Applications . . . . . . . . . . . . . . . . . . . . . . . 15

3 conclusion 17

4 Reference 18

1

List of Figures

1.1 Physicist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Superconducting material repel magnet . . . . . . . . . . . . . 41.3 graphic courtesy Quantum Design . . . . . . . . . . . . . . . . 51.4 A Magnet Levitating Above a High-Temperature Supercon-

ductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.5 The Evolution of the Superconducting Transition Temperature 7

2.1 Superconducting Magnet Wire of Niobium-Titanium . . . . . 92.2 The Superconducting Super-Collider project planned for con-

struction in Ellis county, Texas . . . . . . . . . . . . . . . . . 92.3 Superconducting Magnet Coils . . . . . . . . . . . . . . . . . . 102.4 Magnetic levitation . . . . . . . . . . . . . . . . . . . . . . . . 112.5 Japan has a demonstration line in Yamanashi prefecture where

test trains JR-Maglev MLX01 have reached 581 km/h (361mph), slightly faster than any wheeled trains . . . . . . . . . . 12

2.6 Principle of maglev and use of superconductors . . . . . . . . 122.7 Cross Sections Of Two Typical Filamantary Composites Of

NbTi In A Copper Matrix . . . . . . . . . . . . . . . . . . . . 122.8 Magnetometer . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.9 Hypres Superconducting Microchip, Incorporating 6000 Joseph-

son Junctions . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.10 American Superconductor unveiled a 5000-horsepower motor

made with superconducting wire. Even larger 36.5MW HTSship propulsion . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2

Chapter 1

INTRODUCTION

Superconductors materials that have no resistance to the flow of electric-ity,are one of the last great frontiers of scientific discovery.Not only have thelimits of superconductivity not yet been reached, but the theories that ex-plain superconductor behavior seem to be constantly under review. In 1911superconductivity was first observed in mercury by Dutch physicist HeikeKamerlingh Onnes of Leiden University (shows in fig 1.1 ). When he cooledit to the temperature of liquid helium, 4 degrees Kelvin (-452F, -269C) , itsresistance suddenly disappeared . The Kelvin scale represents an ”absolute”scale of temperature. Thus, it was necessary for Onnes to come within 4degrees of the coldest temperature that is theoretically attainable to witnessthe phenomenon of superconductivity. Later, in 1913 he won a Nobel Prizein physics for his research in this area.

The next great milestone in understanding how matter behaves at ex-treme cold temperatures occurred in 1933. German researchers WaltherMeissner (above) and Robert Ochsenfeld (above) discovered that a supercon-ducting material will repel a magnetic field (below fig.1). A magnet movingby a conductor induces currents in the conductor. This is the principle onwhich the electric generator operates. But, in a superconductor the inducedcurrents exactly mirror the field that would have otherwise penetrated the

Figure 1.1: Physicist

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Figure 1.2: Superconducting material repel magnet

superconducting material - causing the magnet to be repulsed. This phe-nomenon is known as strong diamagnetism and is today often referred to asthe ”Meissner effect” (an eponym). The Meissner effect is so strong that amagnet can actually be levitated over a superconductive material.

In subsequent decades other superconducting metals, alloys and com-pounds were discovered. In 1941 niobium-nitride was found to super con-duct at 16 K. In 1953 vanadium-silicon displayed superconductive prop-erties at 17.5 K. And, in 1962 scientists at Westinghouse developed thefirst commercial superconducting wire, an alloy of niobium and titanium(NbTi). High-energy, particle-accelerator electromagnets made of copper-clad niobium-titanium were then developed in the 1960s at the Rutherford-Appleton Laboratory in the UK, and were first employed in a superconduct-ing accelerator at the Fermilab Tevatronin in the US in 1997 .

The first widely-accepted theoretical understanding of superconductivitywas advanced in 1957 by American physicists John Bardeen, Leon Cooper,and John Schrieffer . Their Theories of Superconductivity became know asthe BCS theory - derived from the first letter of each man’s last name -and won them a Nobel prize in 1972. The mathematically complex BCStheory explained superconductivity at temperatures close to absolute zerofor elements and simple alloys. However, at higher temperatures and withdifferent superconductor systems, the BCS theory has subsequently becomeinadequate to fully explain how superconductivity is occurring.

Another significant theoretical advancement came in 1962 when Brian D.Josephson , a graduate student at Cambridge University, predicted that elec-trical current would flow between two superconducting materials - even whenthey are separated by a non-superconductor or insulator. His prediction waslater confirmed and won him a share of the 1973 Nobel Prize in Physics.This tunneling phenomenon is today known as the ”Josephson effect” and

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Figure 1.3: graphic courtesy Quantum Design

has been applied to electronic devices such as the SQUID, an instrument ca-pabable of detecting even the weakest magnetic fields(show in fig 1.3 graphic).

The term Superconductivity is a phenomenon occurring in cer-tain materials at extremely low temperatures, characterized by ex-actly zero electrical resistance and the exclusion of the interiormagnetic field (the Meissner effect). The electrical resistivity of a metal-lic conductor decreases gradually as the temperature is lowered. However, inordinary conductors such as copper and silver, impurities and other defectsimpose a lower limit. Even near absolute zero a real sample of copper showsa non-zero resistance. The resistance of a superconductor, on the other hand,drops abruptly to zero when the material is cooled below its ”critical temper-ature”. An electrical current flowing in a loop of superconducting wire canpersist indefinitely with no power source. Like ferromagnetism and atomicspectral lines, superconductivity is a quantum mechanical phenomenon. Itcannot be understood simply as the idealization of ”perfect conductivity” inclassical physics.

Superconductivity occurs in a wide variety of materials, including simpleelements like tin and aluminium, various metallic alloys and some heavily-doped semiconductors. Superconductivity does not occur in noble metals likegold and silver, nor in most ferromagnetic metals. In 1986 the discovery ofa family of cuprate-perovskite ceramic materials known as high-temperaturesuperconductors, with critical temperatures in excess of 90 Kelvin, spurredrenewed interest and research in superconductivity for several reasons. As atopic of pure research, these materials represented a new phenomenon notexplained by the current theory. And, because the superconducting state per-sists up to more manageable temperatures (past the economically-importantboiling point of liquid nitrogen), more commercial applications are feasible,especially if materials with even higher critical temperatures could be dis-covered.

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Figure 1.4: A Magnet Levitating Above a High-Temperature Superconductor

BCS Theory: The first widely-accepted theory to explain superconduc-tivity put forth in 1957 by John Bardeen, Leon Cooper, and John Schreiffer.The theory asserts that, as electrons pass through a crystal lattice, the lat-tice deforms inward towards the electrons generating sound packets knownas ”phonons”. These phonons produce a trough of positive charge in the areaof deformation that assists subsequent electrons in passing through the sameregion in a process known as phonon-mediated coupling. This is analogousto rolling a bowling ball up the middle of a bed. 2 people, one lying on eachside of the bed, will tend to roll toward the center of the bed, once the ballhas created a depression in the mattress. And, a 2nd bowling ball, placed atthe foot of the bed, will now, quite easily, roll toward the middle.

Josephson Effect: A phenomenon named for Cambridge graduate stu-dent Brian Josephson, who predicted that electrons would ”tunnel” througha narrow (¡10 angstroms) non-superconducting region, even in the absenceof an external voltage. In a normal conductor, electrical current only flowswhen there’s a voltage differential and contiguous electrical connection. Ithas been theorized that the Josephson Effect arises from the incoherent phaserelationships between superconducting electrons in the two (separated) su-perconductors. The AC Josephson Effect is where the current flow oscillatesas an external magnetic field impinged upon it increases beyond a criticalvalue. [at a frequency of 2eV/h, where e is the electron charge, V is thevoltage that appears, and h is Planck’s constant].

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Figure 1.5: The Evolution of the Superconducting Transition Temperature

7

Chapter 2

Applications ofSuperconductivity

1. Superconducting Magnets

2. Power Transmission

3. Transportation (MAGLEV Trains)

4. Electric Motors

5. SQUID Magnetometers

6. Electronics

7. Military applications

2.1 Superconducting Magnets

Type II superconductors such as niobium-tin and niobium-titanium are usedto make the coil windings for superconducting magnets. These two materialscan be fabricated into wires and can withstand high magnetic fields. Typicalconstruction of the coils is to embed a large number of fine filaments ( 20 mi-crometers diameter) in a copper matrix. The solid copper gives mechanicalstability and provides a path for the large currents in case the supercon-ducting state is lost. These superconducting magnets must be cooled withliquid helium. Superconducting magnets can use solenoid geometries as doordinary electromagnets.

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Figure 2.1: Superconducting Magnet Wire of Niobium-Titanium

Figure 2.2: The Superconducting Super-Collider project planned for con-struction in Ellis county, Texas

Superconducting Magnet Wire of Niobium-Titanium Ohanian’sPhysics has a photograph of a cross- section of copper wire of diameter 0.7mm with 2100 filaments of niobium-titanium embedded in it. This is anapproximate sketch of the geometry. Although copper is one of the bestroom- temperature conductors, it acts almost as an insulator between thestrands.(shown in fig2.1)

Uses of super conducting magnets

1. Most high energy accelerators now use superconducting magnets.

2. The sub atomic particles can be accelerated near to speed of light bythe use of the super magnets

3. The proton accelerator (proton-antiproton collider) at Fermi lab uses774 superconducting magnets in a ring of circumference 6.2 kilometers.

Argonne Bubble Chamber

1. As an example of the energy savings attainable with superconductingmagnets.

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Figure 2.3: Superconducting Magnet Coils

2. A bubble chamber at Argonne National Laboratory has a 4.8 meterdiameter magnet producing a magnetic field of 1.8 Tesla.

3. After establishing the magnetic field, only about 190 kW is required tomaintain the liquid helium refrigeration.

2.2 Power Transmission

Almost10% to 15% of generated electricity is dissipated in resistive lossesin transmission lines, the prospect of zero loss superconducting transmis-sion lines is appealing. In prototype superconducting transmission lines atBrookhaven National Laboratory, 1000 MW of power can be transportedwithin an enclosure of diameter 40 cm. This amounts to transporting theentire output of a large power plant on one enclosed transmission line. Thiscould be a fairly low voltage DC transmission compared to large transformerbanks and multiple high voltage AC transmission lines on towers in the con-ventional systems. The superconductor used in these prototype applicationsis usually niobium-titanium, and liquid helium cooling is required. Currentexperiments with power applications of high-temperature superconductors fo-cus on uses of BSCCO in tape forms and YBCO in thin film forms. Currentdensities above 10,000 amperes persquare centimeter are considered neces-sary for practical power applications, and this threshold has been exceededin several configurations.

Practical examples of super conductivity lines

1. In May of 2001 some 150,000 residents of Copenhagen, Denmark, be-gan receiving their electricity through HTS (high-temperature super-

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Figure 2.4: Magnetic levitation

conducting) material. That cable was only 30 meters long, but provedadequate for testing purposes.

2. In the summer of 2001 Pirelli completed installation of three 400-footHTS cables for Detroit Edison at the Frisbie Substation capable ofdelivering 100 million watts of power. This marked the first time com-mercial power has been delivered to customers of a US power utilitythrough superconducting wire.

2.3 Transportation (Maglev Trains)

Magnetic levitation transport, or maglev, is a form of transportation thatsuspends, guides and propels vehicles (especially trains) using electromag-netic force. This method is faster than wheeled mass transit systems, po-tentially reaching velocities comparable to turboprop and jet aircraft (900km/h, 559 mph). These trains use superconducting magnets which allow fora larger gap, and repulsive-type Electro-Dynamic Suspension (EDS). It isnot practical to lay down superconducting rails, it is possible to construct asuperconducting system onboard a train to repel conventional rails shown infig 2.4.

MAGLEV vehicles based on superconducting magnets operate with sim-ple coils of superconducting wire and compact cryogenic coolers. Maglev ishighly reliable, and operates in a highly redundant manner with a very largemargin of safety.

The maglev trains uses a commercially manufactured NbTi superconduc-tor, (Maglev magnets).

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Figure 2.5: Japan has a demonstration line in Yamanashi prefecture wheretest trains JR-Maglev MLX01 have reached 581 km/h (361 mph), slightlyfaster than any wheeled trains

Figure 2.6: Principle of maglev and use of superconductors

The ultra-fine filaments of NbTi alloy, each a few microns in diameter,are imbedded in a matrix of high electrical conductivity copper. The over-all diameter of the composite NbTi/copper superconducting wire is typicallyabout 1 millimeter.

The wire is then wound into an appropriate configuration to form theMaglev magnet.

Figure 2.7: Cross Sections Of Two Typical Filamantary Composites Of NbTiIn A Copper Matrix

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Figure 2.8: Magnetometer

2.4 Electric Motors

Superconducting motors and generators could be made with a weight of aboutone tenth that of conventional devices for the same output.

It is possible to build very large capacity generators for power plantswhere structural strength considerations place limits on conventional gener-ators.

In 1995 the Naval Research Laboratory demonstrated a 167 hp motor withhigh-Tc superconducting coils made from Bi-2223. It was tested at 4.2K andat liquid neon temperature, 28K with 112 hp produced at the higher temper-ature.SQUIDs (Superconducting Quantum Interfering Devices) are amongthe most sensitive devices known to man, certainly the most sensitive mag-netic field detectors.

The SQUID was introduced by James Zimmerman in the late 1960s.It isessentially an ultra sensitive detector of magnetic flux, made up of a super-conducting ring interrupted by one or two Josephson Junctions. A SQUIDis capable of detecting magnetic fields of around 2 pT. It has however beendemonstrated that fields of around 100 fT are also within the scope of aSQUID It is typically required to be kept at temperatures of around 4.2Kelvin.The device may be configured as a magnetometer to detect incrediblysmall magnetic fields.shown in fig 2.8

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Figure 2.9: Hypres Superconducting Microchip, Incorporating 6000 Joseph-son Junctions

2.5 Electronics

The National Science Foundation, along with NASA and DARPA and var-ious universities are currently researching Petaflop” computers. A Petaflopis a thousand-trillion floating point operations per second. Today’s fastestcomputing operations have only reached ”teraflop” speeds - trillions of op-erations per second. Currently the fastest is one of the IBM Blue Gene Lcomputers running at 280.6 teraflops per second (with multiple CPU’s). Thefastest single processor is a Lenslet optical DSP running at 8 teraflops It hasbeen conjectured that devices on the order of 50 nanometers in size alongwith unconventional switching mechanisms, such as the Josephson junctionsassociated with superconductors, will be necessary to achieve such blisteringspeeds. TRW researchers (now Northrop Grumman) have quantified thisfurther by predicting that 100 billion Josephson junctions on 4000 micropro-cessors will be necessary to reach 32 petabits per second. These Josephsonjunctions are incorporated into field-effect transistors which then becomepart of the logic circuits within the processors information. It is, however,not a foregone conclusion that computers of the future will be built aroundsuperconducting devices.(shown in fig 2.9)

In the electronics industry, ultra-high-performance filters are now beingbuilt. (Since superconducting wire has near zero resistance, even at highfrequencies, many more filter stages can be employed to achieve a desired fre-quency response. This translates into an ability to pass desired frequenciesand block undesirable frequencies in high-congestion RF (radio frequency)applications such as cellular telephone systems. ISCO International and Su-perconductor Technologies are companies currently offering such filters). Su-perconductors have also been used to make digital circuits (e.g. based on theRapid Single Flux Quantum technology) and RF and microwave filters formobile phone base stations.

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Figure 2.10: American Superconductor unveiled a 5000-horsepower motormade with superconducting wire. Even larger 36.5MW HTS ship propulsion

2.6 Military Applications

Smaller motors are being built for NAVY ships using superconducting wireand tape.

1. HTSC SQUIDS are being used by the U.S. NAVY to detect mines andsubmarines.

2. The newest application for HTS wire is in the degaussing of navalvessels. (Degaussing of a ship’s hull eliminates residual magnetic fieldswhich might otherwise give away a ship’s presence. In addition toreduced power requirements, HTS degaussing cable offers reduced sizeand weight.

3. The most ignominious military use of superconductors may come withthe deployment of ”E-bombs”. These are devices that make use ofstrong, superconductor-derived magnetic fields to create a fast, high-intensity electro-magnetic pulse (EMP) to disable an enemy’s electronicequipment.

4. The military is also looking at using superconductive tape as a meansof reducing the length of very low frequency antennas employed onsubmarines. Normally, the lower the frequency, the longer an antennamust be. However, inserting a coil of wire ahead of th

5. Antenna will make it function as if it were much longer. Unfortunately,this loading coil also increases system losses by adding the resistancein the coil’s wire. Using superconductive materials can significantlyreduce losses in this coil.

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6. Applications engineers suggest that superconducting carbon Nanotubesmight be an ideal Nano-antenna for high-gigahertz and terahertz fre-quencies, once a method of achieving zero ”on tube” contact resistanceis perfected.

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Chapter 3

conclusion

All of this is, of course, contingent upon a linear growth rate. Should new su-perconductors with higher transition temperatures be discovered, growth anddevelopment in this exciting field could explode virtually overnight.The fu-ture melding of superconductors into our daily lives will also depend to a greatdegree on advancements in the field of cryogenic cooling.New, high-efficiencymagneto caloric-effect compounds such as gadolinium-silicon-germanium areexpected to enter the marketplace soon. Such materials should make pos-sible compact, refrigeration units to facilitate additional HTS applications.Another impetus to the wider use of superconductors is political in nature.The reduction of green-house gas (GHG) emissions has becoming a topicalissue due to the Kyoto Protocol which requires the European Union (EU) toreduce its emissions by 8% from 1990 levels by 2012. Physicists in Finlandhave calculated that the EU could reduce carbon dioxide emissions by upto 53 million tons if high-temperature superconductors were used in powerplants.

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Chapter 4

Reference

1. S.M.Szed, Physics of Semiconductor, Wiley Eastern Ltd, New Delhi(1988).

2. American Chemical Society, Chemistry of High Temperature Super-conductor, Washington.D.C.Vol.XI,1987.

3. Hunt Daniel V, Superconductivity Source Book, John Wiley and Sons.inc.1989.

4. M Deppu, High Temperature Superconducting Material, New York,1988.

5. Power Application of Superconductivity, IEEE explorer.org/ielis/852/2490.

6. Van Dozer and Turner C.W., Principles of Superconductive Devicesand Circuits, London, Arnold,1981.

7. Schechter, Bruce. The Path of No Resistance, Simon and Schuster,1987.

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