Operation of Trapatt Oscillators under Transient Ionizing Radiation Conditions

The performance of complementary (n+pp+) silicon TRAPATT diodes has been measured under transient ionizing radiation conditions in both evacuated and airfilled coaxial cavities. Twenty-five watt pulsed, 2.5 GHz oscillators were exposed to 100 nanosecond pulses of 10 MeV electrons at dose rates between 2 × 107 and 4 × 109 rads/sec. The RF power is unaffected below a critical dose rate, which is typically between 8 × 107 and 2 × 108 rads/sec. Above this critical dose rate the RF power is almost quenched entirely during the radiation pulse, but recovers to the original level within 50 nanoseconds afterwards for all dose rates used. Rapid recovery of original RF power levels occurred when the radiation pulse occurred at the initiation of the 300 nanosecond RF TRAPATT pulse, in the middle of the TRAPATT pulse, or during the decay of the TRAPATT pulse. The RF power during the radiation pulse is in agreement with a first order model of TRAPATT operation, in which the principal effect of the radiation pulse is a reduction in mobile charge generated by the avalanche shock front. The decreased mobile charge reduces the time required to remove the trapped plasma and the time necessary for recovery of the diode voltage, thereby decreasing TRAPATT power.