Cyclotron resonance maser experiments in a bifilar helical waveguide

Abstract

Oscillator and amplifier cyclotron-resonance-maser (CRM) experiments in a spiral bifilar waveguide are presented in this paper. The slow-wave CRM device employs a low-energy low-current electron beam (2-12 keV, approximately 0.5 A). The pitch angle of the helical waveguide is relatively small; hence, the phase velocity in this waveguide, V(ph) congruent with0.8c (where c is the speed of light), is much faster than the axial velocity of the electrons, V(ez)</=0. 2c. Thus traveling-wave-tube-type interactions are eliminated in this device. According to the CRM theory, the dominant effect in this operating regime, V(ez)<V(ph)<c, is the axial (Weibel) bunching mechanism rather than the opposed azimuthal bunching mechanism. In an oscillator mode, the CRM output frequency is tuned continuously in the range 2.5-8.4 GHz by varying the axial magnetic field. A fine-tuning is possible by the electron accelerating voltage. In the amplifier mode, this CRM experiment demonstrates an amplification up to 16 dB at 5 GHz. The immediate gain bandwidth is wider than 0.1 GHz (>2%). The wide tunable range of this CRM device due to the nondispersive bifilar helix is discussed.