Effects of relaxation in levitating superconductors

Magnetic Relaxation - Methods for Stabilization of Magnetization and Levitation Force

“…The experimental setup is described in the paper of Smolyak et al (2002). The sample of melt-textured Yba 2 Cu 3 O 7 ceramics (disk 10 mm in diameter and 3.5 mm high) and the ring magnet are used in the experiments.…”

“…The direct measurements of the interaction force between magnet and superconductor (Moon et al, 1990;Riise et al, 1992;Smolyak et al, 2002) showed a considerable decrease of the force with time. However, in the experiments, where the drift of levitating HTS samples was observed, the levitation height did not change in the stationary magnetic field (Krasnyuk & Mitrofanov, 1990;Terentiev & Kuznetsov, 1992).…”

“…The magnetic field with azimuthal symmetry is usually created by disk or ring permanent magnets, and in some cases B r (r) can be approximated by a linear dependence. Then the expression for the force (3) may be written as (Smolyak et al, 2002):…”

“…(5) , and also assuming the relaxation term in Eq. (11) is small as compared to unity, one may write (here and in the sections 3.3 and 3.4 we use the results received by Smolyak et al, 2002):…”

“…A classical paper on the flux creep (Beasly et al, 1969) probably was the first to note that the total magnetic flux in superconductor remains unchanged for a long time after the small reversal of external magnetic field. This effect was studied later in more detail, and it formed the basis of the reverse methods for the stabilization of magnetization (Kwasnitza & Widmer, 1991, 1993 and levitation force (Smolyak et al, 2000(Smolyak et al, , 2002. The reversal leads to the internal magnetic relaxation (Smolyak et al, 2001) when the volume-averaged quantities do not change for a long time.…”