Microwave amplification using an unstable electron beam in crossed electric and magnetic fields

The paper describes an experiment in which the amplitude of the microwave signal on a velocity-modulated strip electron beam in crossed electric and magnetic fields was measured as a function of position along the beam by means of a moving cavity. Amplification of this signal was detected, the growth rate being of the order of 2dB/cm for a 500 eV beam with a current of 40 mA per centimetre of beam width. This agrees reasonably well with theoretically predicted values. The possibility of using this amplification process for high-power tubes and v.h.f. generators is discussed.