Aspects of M-type interaction, with particular reference to the backward-wave magnetron amplifier

The paper describes an experimental 2-circuit backward-wave magnetron amplifier. Under static conditions the instability effects in the magnetron beam are found to affect the proper focusing of the electron beam. An analytical model of the d.c. beam is suggested, and it is shown that the behaviour of the start-of-oscillation current as a function of the magnetic field predicted by this model is in approximate accordance with experimental results. The analytical model shows high theoretical gains for the amplifier, and, experimentally, a maximum stable gain of 20 dB was measured under low-level operating conditions. The gain was found to be sensitive to beam position and focusing conditions. For magnetron operation, saturation effects will limit the usefulness of the amplifier as a high-level device.