An experimental study of large-signal behaviour in M-type valves in the presence of space charge by the use of an analogue method

The paper is concerned with the use of a new analogue method for the study of the high-frequency bunching in an electron beam in interaction with a slow wave in crossed electric and magnetic fields. For an observer moving at the same velocity and in the same direction as the slow wave, supposed of constant amplitude (case of the magnetron), the electric field of the wave appears as purely static; for this observer, the high-frequency motion in the beam is not modified; and a drift of the total beam parallel to the magnetic field does not introduce any new force or bring any change to the transverse motions of the electrons. The method consists in reconstructing artificially in the laboratory frame of reference the observations made in the moving frame. This is achieved by using a flat or hollow beam subjected to electrostatic fields which simulate the r.f. slow wave and drift parallel to the applied magnetic field (O-type beam). The electrons are intercepted by a fluorescent screen on which the image of the bunching is displayed.