The Role of Quench-Back in the Passive Quench Protection of Uncoupled Solenoids in Series With and Without Coil Sub-Division

Abstract

Abstract-This paper is the final paper in a series of papers that discusses passive quench protection for high inductance solenoid magnets [1], [2]. This report describes how passive quench protection system may be applied to superconducting magnets that are connected in series but not inductively coupled. Previous papers have discussed the role of magnet sub-division and quench back from a conductive mandrel in reducing the hot-spot temperature and the peak coil voltages to ground. When magnets are connected in series, quench-back from a conductive mandrel can cause other magnets in a string to quench even without inductive coupling between magnets. The magnet mandrels must be well coupled to the magnet circuit that is being quenched. When magnet circuit sub-division is employed to reduce the voltages-to-ground within magnets, the resistance across the subdivision becomes the most important factor in the successful quenching of the magnet string.Index Terms-Quench-back, Sub-division quench protection

Unbalanced Quenching in a Long Solenoid With Separately Powered Coils

“…Heat generated in the E2 coil spreads to the center coil by heat diffusion. Once the center coil starts to quench, quench back occurs relatively quickly (in ~1.0 s) [9]. Without quench back, the quench propagation in the long solenoid would be ~7 s. The G10 spacers between coils and bobbin slow down quench propagation and quench-back.…”

“…Unlike the quenches in the short coils, a quench in the long solenoid C is greatly speeded up by quench-back from the 6061-Al mandrel [8]. A quench in one coil will quench the whole magnet [9].…”