Analysis and Management of Thermal Energy Release During Quench in a Superconducting Magnet

Abstract

In low temperature superconducting (LTS) magnets built using (cryogenic) liquid cooled superconductors, such as those designed for particle accelerators and thermonuclear fusion reactors, the operating stability and quench (sudden transition from superconducting to normal state) is a complex phenomenon. In most cases, the quenched magnet is isolated from the rest of the cryogenic system and the cryogenic fluid (helium) is expelled from the cryostat via a pressure relief valve (PRV) to prevent over-pressurization. This loss of cryogenic coolant (release to atmosphere), as well as the associated stored refrigeration results in increased operational cost (to replenish the helium), and recovery time for the LTS magnet to be operational following a quench. A novel concept for energy and cryogenic inventory management during a LTS magnet quench using direct contact (fluid mixing) heat exchange in a cryogenic buffer volume has been proposed and demonstrated. Development of a semi-analytical, one-dimensional, transient model to predict the boil-off flow generated during a quench, and the subsequent energy absorption (and pressurization) in the cryogenic buffer volume is discussed. The developed model can be used as a simplified tool for process and mechanical design of such a system.