super conductors
TRANSCRIPT
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