On the flux jumps in hard superconductors

Abstract

The paper is devoted to the investigation of critical state stability against flux jumps in hard superconductors accounting the critical current density dependence on the temperature and magnetic field. A flat sample with finite thickness is considered. The stability criteria were found for the Kim-Anderson critical state model as well as for the region close to the upper critical field Ha,. It was shown that the stability diminishes near Ha,. The stability conditions were found for the total range of external fields below Ho,. It was found that under certain conditions the magnetic instabilities may develop in two isolated regions of the external fields.

EMP Effects on High-<tex>$T _c$</tex>Superconducting Devices

“…The shape of these regions and the damage process dynamics makes it possible to conclude that they appear as a result of thermomagnetic instability [13] induced by fast magnetic flux jumps at the edge of the film. Such instability is typical for hard type II superconductors exposed to alternating magnetic fields [14]. Fast changes in the magnetic field generate electrical currents that heat the superconductor and induce avalanche penetration of the magnetic fluxoid structure toward the superconductor.…”

Thermo-magnetic instabilities in Nb₃Sn superconducting accelerator magnets

“…This section shows a less restrictive criterion which takes into account the dynamic effect of thermal diffusion inside the conductor. These criteria are derived by linearizing the full set of the equations which describe thermo-magnetic instabilities, including the thermal diffusion [73,74,75,76,77,78]. Also presented will be how these criteria affect the strand design.…”

“…where B S is the magnetic field at the conductor surface. The stability of the critical-state for an arbitrary dependence of j c on B has been analyzed elsewhere [74,77]. The thermal balance and Maxwell equations describing thermo-magnetic instabilities in superconductors are:…”

Effect of flux flow on self-field instability

“…This dissipation is easily estimated using the "frozen-flux" approximation of Kremlev, Mints, and Rakhmanov. 6 In the frozen-flux approximation, the current leaving the filaments remains in the copper of the outer sheath of saturated filaments. Hence the average current density there (averaged over a volume containing a few filaments) is constant and equal to nJc(Tb)' where Jc(Tb) is th~ critical current density at the ambient bath temperature Tb.…”