On the Mechanical Behavior of a Nb3Sn Superconducting Coil During a Quench: Two-Dimensional Finite Element Analysis of a Quench Heater Protected Magnet

Abstract New high-field accelerator magnets based on Nb3Sn superconductors are pushing the boundaries of magnet design and quench protection towards new limits. While their large stored energies and current densities result in a very challenging scenario for magnet protection, their great electromagnetic forces create also new requirements in terms of magnet design and stress management techniques. Furthermore, the strain sensitivity of Nb3Sn cables turns the electro-mechanical limits of the conductor into a parameter of the highest importance, where conductor degradation becomes a critical aspect in magnet operation. The coupling of all the above-mentioned considerations during a quench is a case of special interest that adds further complexity to the design of Nb3Sn magnets. The objective of this paper is to provide a complete two-dimensional investigation of the coil and magnet structure mechanics during a quench event. The analysis is performed using a combination of finite element codes that provide the necessary input for the mechanical study. The core of the modelling strategy relies on a thermal-electric model, whose results are directly used as loads in the mechanical simulation. In doing so, the stress evolution during and after a quench is obtained. We focus for this time in the analysis of a quench heater protected magnet, where electro-magnetic dynamic effects are of less importance in contrast to other protection systems like CLIQ.