Study On A No-insulation HTS Coil Impregnated Using Solder And A New Fast-charging Method

In the development of high temperature superconducting(HTS)magnets,no-insulated(NI)HTS coils have been a hot topic,due to its mechanical robustness,higher current density and less risk of partial quenching.In order to use the HTS coil into high magnetic field,NI HTS coils must have stable mechanical properties.To improve the mechanical performance,impregnation methods using epoxy or paraffin are conventionally applied.Since they are non-conducting and their thermal expansion coefficient is different from the HTS tapes,the turn-to-turn resistance between the tapes should be increased.Therefore,this paper proposes a new type of impregnation method,which is impregnated and fixed by using conductive material,solder.In this paper,various HTS coils were prepared,and basic electrical characteristics of the solderimpregnated coil were studied including voltage-current tests,chargedischarge tests,and sudden-discharge tests.The experiment results show that the solder-impregnated coil still contains the characteristics of NI HTS coil.As the results illustrate that the charge delay of the NI coil after solder impregnation is too long.In order to reduce the charge delay,this paper proposes a proportional-integrated(PI)negative feedback control to shorten the charge delay.Experiments show that the NI coil using the PI feedback control can reduce the time to reach the target magnetic field from350 s to 20 s,and the relative overshoot is controlled within 4% with PI control.The research results in this paper reveal that the solder impregnation is a feasible way for impregnation,and verify the PI control is an efficient way to reduce the charge delay of NI coils,which provides a new idea for the future research and application of NI HTS coils.