MEGAWATT, 330 HZ PRF TUNABLE GYROTRON EXPERIMENTS

Repetitively pulsed and cw gyrotrons have hitherto used thermionic cat hodes, whereas cold cathode gyrotrons have normally operated as 'singl e shot' devices. The novel results presented here show that cold catho de gyrotrons can be successfully pulsed repetitively. A tunable gyrotr on with a pulse repetition frequency (PRF) of 150Hz is demonstrated. T his system developed >4MW mm-wave output pulses at 100GHz. The gyrotro n is based on a two-electrode configuration comprising a field-immerse d, field emission, cold cathode and a shaped anode cavity. A supercond ucting magnet was used to produce the homogeneous intra-cavity magneti c field and a cable pulser was used to produce the drive the electron beam. This pulser produced up to a (200+/-20)kV pulse with 10ns rise t ime, a 100ns flat top, a 10ns decay with a characteristic impedance of 200OMEGA. The energy storage capacity of the cable pulser was 3.5J. T he charging unit limited the maximum PRF to 330Hz. Due to spark gap sw itching limitations 330Hz was only obtainable in 5 to 10 pulse bursts. For substantial periods of the order of 30 seconds, 100Hz PRF was ach ieved over an oscillating range of 28 to 100GHz and 150Hz PRF was achi eved at 80GHz. No degradation effects on the mm-wave output pulse was evident due to diode recovery time throughout this series of results. A subsequent conclusion is that the diode recovery time in our cold ca thode gyrotron is less than 3ms.