Evaluation of Characteristics of PTFE Coating for Insulation of HTS Coils for Medical Particle Accelerators

In this study, the applicability of a PTFE (Polytetrafluoroethylene) spray-coated insulation layer for high-temperature superconducting (HTS) coils used in medical particle accelerator systems was experimentally investigated. Prior to coil fabrication, the fundamental reliability and insulation characteristics of the PTFE coating were systematically evaluated. PTFE coatings were applied to REBCO (Rare-Earth Barium Copper Oxide) tapes and STS 304-based specimens, and mechanical stability was examined through bending and folding tests, while thermal reliability was assessed under repeated cooling–heating cycles between room temperature (293 K) and liquid nitrogen temperature (77 K). Electrical insulation performance was evaluated through dielectric breakdown tests using sphere–plane and turn-to-turn electrode configurations, and the breakdown voltage corresponding to a 63.2% probability was obtained via Weibull analysis. In addition, the effect of the coating process on superconducting performance was examined by measuring the critical current of REBCO tapes before and after coating at liquid nitrogen temperature. The results showed that the PTFE coating maintained mechanical and thermal stability without noticeable degradation, exhibited increased dielectric strength with increasing coating cycles, and caused no significant change in critical current (Ic). These results indicate that PTFE spray coating is a promising insulation approach for HTS coils in medical accelerator applications.