Cyclotron resonance maser experiments in a bifilar helical waveguide

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, ∼0.5 A). The pitch angle of the helical waveguide is relatively small; hence, the phase velocity in this waveguide, [Formula Presented] (where c is the speed of light), is much faster than the axial velocity of the electrons, [Formula Presented] Thus traveling-wave-tube-type interactions are eliminated in this device. According to the CRM theory, the dominant effect in this operating regime, [Formula Presented] 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 [Formula Presented] The wide tunable range of this CRM device due to the nondispersive bifilar helix is discussed.