Generation and Resonance Absorption of Doppler Shift Dominated Cyclotron Maser Radiation by an Intense Relativistic Electron Beam

Abstract

Generation of radiation field by an intense, relativistic electron beam moving in a longitudinal magnetic field is studied experimentally in a frequency range of x-band microwave. The electron beam carries a maximum current of 10 kA at voltage of 0.6 MV, with a pulse width of 10 ns. It flows inside a rectangular waveguide immersed in a homogeneous axial magnetic field of 3 to 10 kG, and radiates a microwave pulse during a few ns. The radiation is smoothly tunable over frequencies ranging from 7-12 GHz by varying the applied longitudinal field strength. Analysis of the results obtained in the experiment identifies that the principal mode of the radiation is TE01, and it is generated by the backward wave interaction of fast electron cyclotron wave and an eigenmode TE01 of the waveguide, for cyclotron harmonic number n = 2. The radiation is to be generated with an intrinsic feed-back mechanism relevant to the wave-beam configuration. The output power of the radiation in its peak is in the order of several hundreds kW. Also studied is attenuation of the radiation field injected externally to propagate along the electron beam. Nearly complete absorption of the radiation was found at a particular value of the axial magnetic field. It is concluded that the absorption detected should be the inverse process of the electron cyclotron maser by the intense relativistic beam.