super conductors

11111The world of

Super conductors

INTRODUCTION superconductivity is a phenomenon of zero electrical resistance and expulsion of magnetic fields occurring in certain materials below characteristic critical temperature Like ferromagnetism atomic spectral lines superconductivity is a quantum mechanical phenomenon which is characterized by MEISSNER EFFECT perfect conductor of electricity:-It carries direct currentwith 100% efficiency because no energy is dissipated by resistive heating. Once induced in a superconducting loop, direct can flow undiminished forever

-all previous theories

were unable to describe

Superconductivity

That’s because it

involved new physics:

Quantum Mechanics

The Meissner (and Ochsenfeld) Effectsuperconductors push out magnetic

fields- and keep them out

with constantly- flowing resistance-less currents

this ‘diamagnetic’ property is more fundamental than zero resistance

T > Tc T < Tc

The crystal structures of High-Tc superconducting materials all have copper-oxide CuO2 layers

Crystal structures of high Tc super conductor

TYPE-I SUPER CONDUCTORS

The superconductivity in Type I superconductors is modeled well by the BCS theory. Remarkably, the best conductors at room temperature (gold, silver, and copper) do not become superconducting at all. They have the smallest lattice vibrations, so their behavior correlates well with the BCS Theory The Type I superconductors have been of limited practical usefulness because the critical magnetic fields are so small and the superconducting state disappears suddenly at that temperature. Type I superconductors are sometimes called "soft" superconductors

In super conductivity a type-II superconductor is characterized by the formation of magnetic vortices in an applied magnetic field

Type-II superconductors are usually made of metal alloys or complex oxide ceramics

All high temperature superconductor are type-II superconductors

These include La1.85Ba0.15CuO4, BSCCO, and YBCO(Yttrium-Barium-Copper-Oxide), which is famous as the first material to achieve superconductivity above the boiling point of liquid nitrogen (77 K)

TYPE-II SUPER CONDUCTORS

PINNING OF SUPER CONDUCTORS

Flux pinning is the phenomenon where a superconductor is pinned in space above a magnet

The superconductor must be a type-II superconductor due to the fact that type-I superconductors cannot be penetrated by magnetic fields.

Transmission Lines

• 15% of generated electricity is dissipated in transmission lines

• Potential 100-fold increase in capacity

• BNL Prototype: 1000 MW transported in a diameter of 40 cm

Pirelli Cables & Systems

Telecommunications

• superconductors are used as efficient filters in cellular telephone towers (now 700 worldwide)

• separate signals of individual phone calls.

• Because of electrical resistance, conventional interference filters eat away part of the signal.

Conductus Clearsite system

The dream - “Tomorrow’s Superconducting World”

350 mph levitated Intercity

trains

Underground rapid transit: Heathrow to

Gatwick in 10 minutes

Computing: 1000 times

faster supercomputers

Cargo-carrying

submarines,

all-electric US Navy

Energy Saving:

power lineselectric motors

transformers Medical

Diagnostics:Magnetic

Resonance Imaging SQUID:Brain

activity Heart

function Information

Technology: much faster, wider band communications

magnetically

launched space

shuttle.

Some of these dreams are already reality…

Japanese levitating train has superconducting magnets onboard

Superconducting power cable installed in Denmark

SQUID measureme

nt of neuron-

magnetic signals

(nuclear) magnetic resonance imaging of the brain, in the

field from a superconducting magnet