Sudden-Discharge Cycling Characteristics and Millisecond Dynamic Behaviors of a HTS Stainless-Steel Insulated Double-Pancake Coil With Thin Copper Plates

We have tested an intermediate-sized HTS stainlesssteel (co-wound) insulated double pancake coil (~132 turns per coil) and discovered dynamic effects during sudden discharge on both millisecond and second scales. For soft break, the power supply is turned off suddenly but the shunt resistor (164 milliohm) is still connected; for hard break, a high voltage contactor is used to suddenly open the circuit so that the leads are completely open. Hard break is dangerous to traditionally insulated LTS magnets, but the SS-insulated HTS DPC retained integrity over >80 chargedischarge cycles. Voltage decay curves for soft and hard breaks are studied on short and long timescales. On long timescales, we observe the expected exponential decay and measure the time constant to calculate contact resistance. On short timescales, we observe highly dynamic effects: a hyper-exponential decay suggesting that the inductance or contact resistance is suddenly changing with time, likely an indication of the RL circuit forming. Moreover, peak voltage immediately (ms) after the sudden discharge were collected and compared. It is found that the peak voltage in soft-discharge is proportional to the applied current, while the those in hard-break has an unique pattern and tends to stay flat even though the applied current increases.