Evaluation of Frequency Loss Induced Quench Protection Prototype at 77 K Using HTS Coils

Abstract

A prototype design of the Frequency Loss Induced Quench (FLIQ) protection system for high temperature superconducting magnets was validated on a small Second-Generation High-Temperature Superconducting (2G HTS) coil. Calorimetric measurements, based on liquid nitrogen boil-off rate, were performed to quantify the heat energy introduced by FLIQ system in the coil. The technique was previously used for steady state AC loss measurements and adopted for the transient losses generated in FLIQ operation. A series of tests of the FLIQ system on 2G HTS pancake coils were performed to study the dynamics of the quench and the energies involved in the quenching process. The results suggest the suitability of the FLIQ technique for quench protection of HTS coils. A measurement protocol of extended repetitive high-frequency current pulses established in the study provided a way to estimate the energy deposited by the AC losses generated in the coil by the FLIQ system. The measurement method described is a practical way to validate the design parameters of the FLIQ system and to evaluate the sensitives of the various design parameters of the FLIQ. The paper reports an experimental technique used to study the sensitivities of various FLIQ design parameters by establishing and measuring quasi-equilibrium heat load and boil-off rate as a result of extended repetitive high-frequency current pulses.