Core Technologies in HTS Coils for Particle-Therapy Accelerators: PRPD-Based Defect Diagnostics and Fast-Ramping Field Response

This paper proposes a non-destructive quality control method for High-Temperature Superconducting (HTS) coils based on Phase-Resolved Partial Discharge (PRPD) analysis. To ensure the safety of expensive REBCO tapes during high-voltage testing, stainless-steel (SS304) tapes with identical geometric dimensions ($0.32\rm{ mm}$thickness,$4\rm{ mm}$width) were utilized as electromagnetic surrogates. We investigated the PRPD signatures of various winding defects, such as protrusions and layer shifts, in pancake coil configurations. The results demonstrate that each defect type produces distinct “Phase-locked clusters,” providing a reliable diagnostic fingerprint for early-stage failure detection. Furthermore, this study evaluates the insulation performance of polytetrafluoroethylene (PTFE) spray coating as a method for achieving tailored insulation levels. Experimental results, including charg…