Speaker
Description
A quench detection and fast discharge scheme has been deployed in the Superconducting Magnet Test Facility at MIT's Plasma Science and Fusion Center for use with high-temperature superconductor (HTS) devices. In particular, the system was developed to protect the SPARC Central Solenoid Model Coil (CSMC), an insulated HTS cable magnet constructed of 40 turns of PIT VIPER cable, as well as the facility's VIPER-cable HTS cold bus and 50 kA binary current leads. Quench detection is realized by classical techniques of voltage measurement with programmable voltage thresholds and hold times, and filters allowing for thresholds less than 10 mV. The configuration fielded for SPARC CSMC tests processed 50 voltage signals in real-time using Siemens PLC hardware. End-to-end response times of ~300 ms, including a programmed 150 ms hold time, were demonstrated with an 8 mV threshold in quench experiments with >30 kA operating current. The fast discharge system comprises a set of four Secheron switchgear in line with the positive bus, each capable of handling 12.5 kA continuously, together with a set of Hubbel dump resistors with variable resistance between ~2 and ~10 mΩ, placed in parallel with the load. Data acquisition and conditioning electronics are protected by a number of Dataforth isolation amplifiers. A voltage limit of 125 V has presently been placed upon the system; this peak voltage was sufficient to safely discharge the CSMC in the event of a quench, while allowing it to reach ~4 T/s during discharge. Desired future work on the system includes improving and testing insulation of the current leads and cold bus to increase this voltage ceiling. The system will next be deployed in service of experiments with Type One Energy's "Magnet Zero" prototype, with an expanded set of voltage tap inputs and an improved response time.
