Numerical Analysis on Quench in a High Temperature Superconducting (HTS) Magnet during Current Dump Process

Abstract

Quench phenomenon was detected while the conduction-cooled HTS magnet was generating 4 T magnetic field. Current dump process was initiated to discharge the magnet energy to the external resistor when the one section of the magnet voltage taps exceeded the voltage criteria. The magnet, however, was permanently damaged during this event. The damaged spot is located where the highest perpendicular field, generated by the magnet, is exposed. As the result of the magnetic energy dissipation in that small spot, the temperature of the conductor increased extremely and reached the melting point of the conductor. The quench spot, however, did not coincide with the section that triggered the current dump process. There was no pre-quench signal from the damaged spot. Non-reversible voltage rise of the damaged spot, however, occurred during the dump process while the current was discharged from the magnet. To investigate the hostile thermal condition of the conduction-cooled magnet, we undertook the simple numerical analysis to calculate the conductor temperature variation during the dump process. The results show that the trends of the temperature change (higher than 300 K or lower than 100 K after the dump process) depending on the initial temperature of the conductor before the current starts to dump. We speculate that even the current-sharing spot was already formed before the dump process, this resistive voltage associated with it was not detected because of long length of the examined conductor section. Both the experimental and calculated results are presented and fully discussed.