Optimum conditions of stabilizer ratio and critical current margin for maximizing the current density of a tightly-wound superconducting magnet

A new stability criterion for a tightly wound superconducting magnet is proposed. In a tightly wound superconducting magnet such as a resin-impregnated or a nonimpregnated magnet, conductor motion within the winding or cracking of epoxy resin often causes a quench of the magnet. Based on an experimental result and theoretical analysis of conductor motion, their time constants were 200 to 500 mu s. The time constant of temperature rise due to heating in a conductor was calculated to be about 20 mu s so that conductor motion can be regarded thermally as a steady-state phenomenon. In a model where the heat due to local steady disturbance is cooled by conduction to both ends of the conductor with a heated length l, the optimum stabilizer ratio and critical current margin for maximizing the current density of the tightly wound superconducting magnet are obtained theoretically. In this theoretical analysis, the stability parameter B, the limited disturbance l/sup 2/ p, and evaluation factor EF are proposed. Stability evaluations on some magnets that were constructed and tested are presented.<>