Operational Validation of a Replacement IGBT for the High Voltage Converter Modulator in a Proton Accelerator at KAERI

A replacement Insulated Gate Bipolar Transistor (IGBT) for the High Voltage Converter Modulator (HVCM) used in the KAERI 100-MeV proton linear accelerator was evaluated following the discontinuation of the original device. The candidate IGBT was assessed through a structured framework combining off-line switch-plate testing and on-line operation in the HVCM driving three klystrons simultaneously. Off-line measurements clarified differences in switching behavior and loss characteristics, while on-line measurements confirmed stable pulse generation under nominal operating conditions. Although the candidate device exhibited a modest increase in total loss energy, its lower junction-to-case thermal resistance resulted in a comparable junction temperature rise. Continuous operation since August 2025 without IGBT-related faults further demonstrates the suitability and long-term reliability of the replacement device in an actual accelerator environment.