A fast oscillator using cyclotron resonance

The use of the cyclotron motion of free electrons inamagnetic field as a source of high frequency oscillations has been discussed for many years, and some experimental success has been achieved [1] [2] [3]. The present paper follows two previous ones, the first of which [4] gave a ballistic theory for the interaction between the electron motion and an r. f. electric field for a number of geometries while the second [5] described an experiment in the two centimetre wavelength region using a crossed field geometry. This experiment showed that the expected oscillation mechanism existed, but that the cathode emission had to be temperature limited and that the power outputs obtainable were only milliwatts. We shall now discuss the reason for this behaviour and describe an electron beam injection system which enables stable space charge limited operation to be achieved, giving an output of tens of watts and making possible more detailed comparison with the theory.