On the force relaxation in the magnetic levitation system with a high-T_csuperconductor

Abstract

The effect of magnetic flux creep on the lift force in a magnet/superconductor system was studied. It was shown experimentally that in the case of real levitation (when a levitating object bears only on a magnetic field) the suspension height and consequently the lift force did not change over a long period of time. When the levitating object is fixed for some time (i.e. a rigid constraint is imposed on it), the levitation height decreases after removal of the external constraint. It is assumed that free oscillations of the levitating object slow down the flux creep process, which is activated when these oscillations are suppressed.

Influence of the magnet aspect ratio on the dynamic stiffness of a rotating superconducting magnetic bearing

“…Other invest igations using a different bearing design found a non-linear stiffness dependence on the cooling height [17,18]. Restricting the linearity to a small range only might be justified with the non-linear magnetic flux density change over larger distances towards the poles of the ring-shaped permanent magnet [19]. However, for distances or cooling heights comparable to the ones studied here, a nearly linear dependence of the dynamic radial stiffness as well as the flux density change in the axial direction was reported by other groups as well [17,19].…”

Study of a cylindrical geometry design for a zero field cooled Maglev system

“…This may be explained by the magnetic relaxation that happens in the YBCO, caused by flux creep. Magnetic relaxation modifies the superconductor current-voltage characteristics, hence will effectively change the current density since magnetic relaxation will establish the HTS internal temperature [13]. Also, and relating to the previous point, the magnetization of the superconductor decays with time as S=(−dM/dLNt)/M 0 , where M 0 is the initial value of magnetization [14].…”

Magnetic levitation using high temperature superconducting pancake coils as composite bulk cylinders

“…Whilst the creep rate was 4.3% per time decade for 77.4 K, it was only 0.89% for 20 K. Given the logarithmic nature of the decay and the very low creep rates for 45 K and lower, the measured force decay behavior is not a concern for the majority of applications. It may also be less of an issue than expected for applications such as flywheels where the levitating body is not rigidly constrained, because creep rates are believed to be significantly lower for bodies which are allowed free oscillations [17].…”