Design Studies of Passive Quench Protection for Superconducting Magnets

Abstract

Quench is a sudden loss of superconductivity that results in a thermal runaway event, where high current and large quantities of stored magnetic energy must be quickly extracted from the superconducting magnet. Methods of quench protection are needed to prevent a hot spot from permanently damaging the superconducting coil. Active methods of quench protection are generally used, but passive methods are simpler and tend to be more reliable. Design studies are performed on the implementation of copper chill plates between radially nested layers of a superconducting solenoid magnet as part of a passive protection scheme. First, a self-contained computational model that couples the superconducting coil quench behavior to the transient thermal and electromagnetic behavior of the passive protection copper chill plates is developed. This first model solves a set of coupled differential equations for the temperatures and currents of the inductively coupled copper chill plates based on an assumed exponentially decaying current distribution. Then this model is further improved by incorporating normal zone resistance propagation relations rather than assuming a current decay distribution. The numerical results of both the assumed exponential current decay model and the normal zone resistance model are validated using LTspice. Finally, a parametric design study is conducted to better inform the design of future radially nested solenoid coil build configurations. The results of this design study suggest that inductively coupled copper chill plates are a viable means of passive quench protection. The normal zone resistance model predicts that 78.2 % of the superconducting coils' initial stored magnetic energy can be dumped into the copper chill plates for the radial build configuration analyzed in this thesis. The use of passive protection copper chill plates was also shown to reduce the maximum temperature and voltage of the coil normal zone after quench compared to when there are no copper plates present. The computational implementation of the normal zone resistance model developed in this thesis provides a powerful design tool for future solenoid coil radial build configurations.