Progress and experimental validation of cryogenic cold cathode gauge sensors for JT-60SA Cryostat

JT-60SA cryostat operation requires robust vacuum diagnostics for machine protection under cryogenic temperatures and strong magnetic fields, where commercial gauges are not fully qualified. This work presents advancements in the development and experimental validation of a Cryogenic Cold Cathode Gauge (C-CCG) system. Two C-CCG prototypes with either aluminum and stainless steel electrodes were tested from room-temperature high-vacuum conditions to cryogenic ultra-high-vacuum conditions, with supply voltages from 1 to 2 kV and magnetic fields of 1 T. Both sensors showed reproducible discharge operation and continuous pressure-current behavior down to 1.5 ⋅ 10 −8 mbar, and maximum response times to He pressure transients estimated at 100 ms. The stainless-steel-electrode sensor proved satisfactory conditions both with and without external magnetic field, while the electrode material had limited impact on the slope of pressure-current characteristics. Gas composition, operating voltage, and magnetic field strongly affected the intensity of the gauge current, highlighting the need for condition-dependent calibration and threshold identification in the protection logic layer. The results support the implementation of C-CCG-based vacuum monitoring systems for superconducting fusion cryostats and support deployment in JT-60SA.