Characteristic of Thyristor in ITER Caused by Neutron Irradiation

The performance of power semiconductor devices near fusion reactors may be changed by the fast neutron irradiation in nuclear fusion. In order to investigate the reliability of thyristors used in a Toroidal Field Fast Discharge Unit (TFFDU), two thyristors KPD5000-52 with almost the same parameters were selected to be irradiated by 14.9 MeV neutrons in the range from 0.403 × 10
⁵
to 1.38 × 10
⁵
n/(cm
²
× s) for 28 h. Metal of thyristor was activated to 3 mSv/h after irradiation, and it decreased to 360 nSv h after 40 days. The electrical parameters of the thyristor, such as the forward/reverse leakage current and on-state voltage were measured under normal junction temperature (25 °C) and high junction temperature (125 °C) respectively. The irradiated thyristors cannot be fully conducted until the gate trigger strength is enhanced to 10 A. Moreover, these devices turn off automatically with a small delay after the gate signal is removed. According to the irradiation theory, this paper also presents the decrease of carrier lifetime, carrier concentration, and mobility, which lead to thyristor failure.