  GTO-like thyristors 5STH-2045H0002 (4.5 kV, 18 kA/us) developed by ABB
semiconductors are currently used at CERN in LHC Beam Dumping System (LBDS):
high-power switches with high dI/dt capability and low turn-on delay time are
required. Implementation of the impact-ionization triggering in GTO-like
thyristor enhances its switching performance and gives new information about
semiconductor physics. In this work thyristors of 5STH-2045H0002 type triggered
in impact-ionization wave mode are investigated. An SOS generator providing a
dV/dt of several kV/ns was used as a source of triggering pulses. A thyristor
switching time of approximately 200-300 ps was observed. Maximum discharge
parameters were obtained for two series connected thyristors at a charging
voltage of 10 kV, and a capacitor stored energy of ~300 J: peak current of 43
kA, dI/dt of 120 kA/us (limited by the discharge circuit), FWHM of 1.5 us. A
single thyristor was tested in the repetitive mode at the charging voltage of
4.2 kV, and the stored energy of 18 J: peak current of 5.5 kA, dI/dt of 40
kA/us, FWHM of 1.5 us were obtained. No thyristor degradation was observed
after more than one million pulses at a PRF up to 1 kHz in burst mode.
Thyristor recovery time was ~250 us. The switching efficiency was up to 98%
depending on dV/dt and stored energy.
