WHAT IS SUPERCONDUCTIVITY??For some materials, the resistivity vanishes at some low

temperature: they become superconducting.

Superconductivity is the ability of certain materials to conduct electrical current with no resistance. Thus, superconductors can carry large amounts of current with little or no loss of energy.

Type I superconductors: pure metals, have low critical field

Type II superconductors: primarily of alloys or intermetallic compounds.

MEISSNER EFFECT

B

T >Tc T < Tc

B

When you place a superconductor in a magnetic field, the field is expelled below TC.

Magnet

Superconductor

Currents i appear, to cancel B.

i x B on the superconductorproduces repulsion.

A superconductor displaying the MEISSNER EFFECT

Superconductors have electronic and magnetic properties. That is, they have a negative susceptibility, and acquire a polarization OPPOSITE to an applied magnetic field. This is the reason that superconducting materials and magnets repel one another.

If the temperature increases the sample will lose its superconductivity and the magnet cannot float on the superconductor.

Record TC versus Year Discovered

0

20

40

60

80

100

120

140

160

180

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

TC (

K)

Hg

NbNNb3Ge

La-Ba-Cu-O

La-Sr-Cu-O

YBa2Cu3O7

Bi2Sr2Ca2Cu3O8

Tl-Ba-Ca-Cu-O

HgBa2Ca2Cu2O8

HgBa2Ca2Cu2O8 Pressure

1986

APPLICATIONS: SuperconductingMagnetic Levitation

The track are walls with a continuous series of vertical coils of wire mounted inside. The wire in these coils is not a superconductor.

As the train passes each coil, the motion of the superconducting magnet on the train induces a current in these coils, making them electromagnets.

The electromagnets on the train and outside produce forces that levitate the train and keep it centered above the track. In addition, a wave of electric current sweeps down these outside coils and propels the train forward.

The Yamanashi MLX01MagLev Train

APPLICATIONS: Medical

The superconducting magnet coils produce a large and uniform magnetic field inside the patient's body.

MRI (Magnetic Resonance Imaging) scans produce detailed images of soft tissues.

APPLICATIONS: Power

Superconducting Transmission CableFrom American Superconductor

The cable configuration features a conductor made from HTS wires wound around a flexible hollow core. Liquid nitrogen flows through the core, cooling the HTS wire to the zero resistance state.

The conductor is surrounded by conventional dielectric insulation. The efficiency of this design reduces losses.