Pulsed electron cyclotron maser experiments

The construction and operation of two pulsed electron cyclotron masers are reported. Measurements of the microwave outputs are presented and compared. The first experiment uses a shielded diode to produce a pulsed electron beam, τ ? 1 μS, 10A ≤ I ≤ 100 A. This annular beam is passed through a multimode cavity to which a magnetic field, which may be varied from 0·1T to 0·6 T, is applied, X-band emissions of up to 100 kW are measured. The second experiment uses a field-immersed diode, which produces an electron beam current of up to 1 kA. The applied magnetic field can also be varied up to 0·6 T in this experiment. Witness-plate results demonstrate that stable beam propagation is achieved. The measured power of the microwave emission is no greater than in the first experiment, but the pulse length is observed to increase by a factor of between 3 and 5, depending upon the conditions, as the magnetic field is increased.