HIGH TEMPERATURE SUPERCONDUCTORS

INTRODUCTION Superconducitivity Beginning of HTS

Historical Background Kamerlingh Onnes, Dutch physicist in 1911 Meissner and Ochsenfeld Niobium nitride-16k, in 1941 Vanadium-silicon-17.5k in 1953 First commercial superconducting wire- NbTI,in 1962

Historical background BCS Theory in 1957 by Bardeen, Cooper and Schrieffer Josephson Effect in1962 Organic superconductors in 1964 HTS in 1986 by Muller & Bednorz Yr,Ba,Cu,O compound- 90k in 1987 Latest ceramic superconductor,Tc=138k, compound of Hg,Ta,Ba,Ca,Cu,O

Conventional superconductor LTS, follows BCS theory Al, Hg, Mo, Nb, Pb

Unconventional Superconductors Mainly artificially made superconductors Cant be explained by BCS theory HTS like La based cuprate perovskite, Mg diboride etc.

Meissner Effect By Walther Meissner & Robert Ochsenfeld At superconducting temperature materials become perfectly dia magnetic & cancels all flux entering inside or the process of excluding the magnetic field Working principle of high speed magnetic trains

Meissner effect

Levitating magnet

Perovskite A rare mineral on the earth crust HTS material Named after the Russian mineralogist L.A.Perovski Also named for the general group of crystals having the same structure Modern HTS are perovskites

High Temperature superconductors Contains Cu oxide planes as a common structural feature Works with the help of liquid N as coolant Doesn’t follow BCS theory Made by mixing oxides & heating in furnaces with adequate oxygen supply

Making of Yr,Ba,Cu,Oxide HTS Mixing the chemicals Calcination Intermediate firings Final oxygen annealing

Even better superconductors Repeating the regrinding & oxygen annealing Using high temperatures for heating Oxygen annealing for long firing periods Grinding the material to a very fine powder before final annealing By protecting from moisture

Testing the superconductors By evaluating the levitating capacity Quality can also be improved by decreasing the air pressure around the system

Type-1 Superconductors Metals & metalloids Generally LTS Also known as soft superconductors Show perfect dia magnetism Pb, La, Ta, Hg

Observation of meissner effect

Type-2 Superconductors Consists of metallic compounds & alloys Metals like Va, Technetium & Niobium HTS materials Hard superconductors Will allow some penetration of external magnetic field into its surface

Type 2 Meissner effect

Atypical and Future Superconductors Fullerene superconductors Organic superconductors Heavy fermions Fluroargentates superconductors Ceramic superconductors Praseodymium 123 superconductors

Atypical & future superconductors Superconducting Niobium wire Hg based ceramic superconductor

Fullerene structure

Ceramic superconductor structure

Organic superconductor structure

Niobium superconductor

Technological applications of superconductivity Magnetometers, digital circuits, MRI, NMR, Control magnets in particle accelerators & fusion reactors, power cables, RF & microwave filters, high speed trains, industrial applications Replacing mechanical bearings

Importance of superconductors Transmission lines Motors Generators Superconducting magnetic energy storage Computers Magnetically levitated trains

HTS Research Areas To develop higher superconducting temperature materials To develop very large current carrying HTS cables To replace mechanical bearings

HTS cables Revolutionized the energy saving concepts Smaller than the conventional Cu & Al cables Higher current carrying capacity Widely used by European, American & Japanese power companies

HTS cables Carry up to 77MVA current at 69 kv transmission voltages Its higher cost of implementation is shadowed by the profit it makes

Alternative HTS cable designs Warm dielectric design Cold dielectric design Triaxial design

Warm dielectric design

Cold dielectric design

Triaxial design

Importance of HTS cables Plays an important role in controlling global warming Prevents the wastage of electrical energy Avoid the need for intermediate sub- stations & transformers for power transmission Energy savings from HTS cables could reach as much as kwh/year

Importance of HTS cables Produces zero energy wastage Can replace the conventional 3 phase power transmitting cables with a single triaxial configuration Avoids the construction of huge transmission towers

Conclusion HTS are the future materials Tomorrow there will be a HTS at our room temperature