Transient Ionizing Radiation Effects on IMPATT Diode Oscillators

The performance of a variety of IMPATT diode oscillators has been measured under transient ionizing radiation conditions, and the results of a large signal model which agrees with experiment are presented. Five hundred milliwatt cw diode oscillators (silicon and gallium arsenide with various types of avalanching junctions) were exposed to 100 nanosecond pulses of 10 MeV electrons at dose rates between 2 × 108 and 8 × 109 rads/sec. With these oscillators, the RF power is reduced at increasing dose rates and is quenched entirely during the radiation pulse at a dose rate dependent upon the DC bias current (greater than 5 × 109 rads/sec for 500 mW oscillators in vacuum). With diodes open to air, oscillators in low Q cavities were quenched during the radiation pulse with a total dose of 500 rads. The results of a large signal theory including the effects of leakage current are presented that agree well with the RF power decrease during irradiation.