The Effect of Twins on Critical Currents of High Tc Superconductors
Interim rept. no 4
CAMBRIDGE UNIV (UNITED KINGDOM)
Pagination or Media Count:
The initial work on levitation forces and separation of superconducting powders has divided into two projects. The first is the nature of the frictional forces and damping on levitated magnets. Although is is reasonable to suppose this arises from AC losses in the superconductor, magnets rotating about their centre of symmetry should not give fluctuating fields and should form almost frictionless bearings. The second is the direct use of magnetic forces to separate particles of superconducting from non superconducting material. The major problem here has been the tendency of fine particles to stick together due to electrostatic forces. To overcome this we have formed a slurry of the material in liquid nitrogen and flash evaporated the nitrogen to blow particles apart. This is reasonably successful but we do not yet know to what extent they will reaglomerate. A second problem is ensuring thermal equilibrium of the particles. This can be done fairly easily in a liquid slurry, but this limits the temperature range we can use and the liquid convection tends to counteract the separation process.
- Electricity and Magnetism