BROADBAND GYRO-TWTs AND GYRO-BWOs
WITH HELICALLY GROOVED WAVEGUIDES
V.L. Bratman, A.W. Cross*, G.G. Denisov, M.Yu. Glyavin, W. He*,
A.G. Luchinin, V.K. Lygin, V.N. Manuilov, A.D. Phelps*, S.V. Samsonov,
M.Thumm**, A.B. VolkovInstitute of Applied Physics, Nizhny Novgorod, 603950, Russia
Frequency-broadband gyro-devices with a novel microwave system in the form of a helically corrugated waveguide are currently under development. The helical corrugation ensures the appearance of an eigenwave with unique properties: namely it possesses a nearly constant group velocity in the region of close-to-zero axial wavenumbers. The use of this operating eigenwave in a gyro-TWT and a gyro-BWO substantially improves their output parameters as compared to analogous gyro-devices based on smooth waveguides .
The main theoretical predictions were first confirmed in proof-of-principle experiments exploiting moderately relativistic (200-300 keV) short-pulse (20-100 ns) field-emission electron beams . An efficiency of 29% and an instantaneous frequency amplification band of 21% were simultaneously obtained in these experiments.
Important progress has recently been achieved in a low-relativistic (80 kV) second-harmonic Ka-band helical-waveguide gyro-TWT which uses a thermionic cathode. This amplifier provides stable amplification with a maximum electronic efficiency of 27%, maximum output power of 180 kW, saturated gain of 25 dB and instantaneous -3 dB bandwidth of nearly 10%.
A helical-waveguide frequency-tunable gyro-BWO, attractive for some technological applications, is also under investigation. In the experiment a pulsed prototype of a 20-kV CW oscillator was developed which generated an output power of about 5 kW with smooth frequency tuning within a frequency range of 23.5-25 GHz.