Flux Jump Stability During Magnetization of Bulk YBCO and Internal Mechanical Stresses in the Trapped Critical State

The question of magnetic- and mechanical stability of bulk superconductors to be charged and operated at a fixed temperature in the flux-trapped critical state is addressed. Based on the temperature- and field-dependent critical current density, Jc(T,H), a new calculation of the temperature dependence of the initial flux-jump field, Hfj(T), appropriate for bulk melt-processed YBCO is presented. Based on the same Jc(T,H), and the usual adiabatic approximation, the sample size dependence of Hfj,(Jc,T) is also included. The Lorentz-force-induced radial- and circumferential internal stresses are calculated in an estimation of the safe operating field range of a flux-trapped cylinder, again of melt-processed YBCO.