Cyclotron resonance maser experiments in a bifilar helical waveguide

Area of Science:

• Physics
• Electrical Engineering
• Wave Phenomena

Background:

• Cyclotron-resonance-maser (CRM) devices are crucial for generating high-frequency electromagnetic waves.
• Traditional CRM designs often face limitations in tunability and interaction efficiency.

Purpose of the Study:

• To investigate the performance of a CRM device utilizing a spiral bifilar waveguide.
• To explore the oscillator and amplifier capabilities of this novel CRM configuration.

Main Methods:

• Experiments were conducted using a slow-wave CRM device with a low-energy electron beam (2-12 keV, ~0.5 A).
• The device features a helical waveguide with a small pitch angle, resulting in a phase velocity (V(ph) ≈ 0.8c) significantly faster than the electron axial velocity (V(ez) ≤ 0.2c).
• This configuration promotes axial (Weibel) bunching over azimuthal bunching, characteristic of the CRM theory in the regime V(ez) < V(ph) < c.

Main Results:

• In oscillator mode, the CRM output frequency was continuously tuned from 2.5 to 8.4 GHz by adjusting the axial magnetic field, with fine-tuning achieved via electron accelerating voltage.
• In amplifier mode, an amplification of up to 16 dB at 5 GHz was demonstrated.
• The device exhibited an immediate gain bandwidth exceeding 0.1 GHz (>2%).

Conclusions:

• The spiral bifilar waveguide CRM effectively eliminates traveling-wave-tube-type interactions.
• The device demonstrates a wide tunable range and significant amplification, attributed to the nondispersive nature of the bifilar helix.
• This CRM configuration shows promise for applications requiring tunable, high-frequency signal generation.