Frequency-multiplying gyrotron traveling-wave tube amplifier

Abstract

Summary form only given. The frequency multiplication was theoretically predicted and verified by experimental observation in a two-stage tapered gyrotron traveling-wave tube amplifier. The electron cyclotron maser interaction at harmonic frequencies was utilized between traveling electromagnetic waves in the two-stage tapered waveguide and the helical electron beam, under the presence of a reduced guiding magnetic field by harmonic operation. A 30 kV, 1 A axis-encircling electron beam from a cusp gun was chosen for both the frequency multiplication and the power amplification. For the theoretical predictions, a small-signal theory was used to investigate the spatial growth rate of the device as a guideline for large-signal simulations. Device performances such as the saturated output power, harmonic frequency multiplication, and electron bunching behavior were numerically analyzed using the large-signal theory and compared with those from particle-in-cell (PIC) code simulations. The dependencies of a bunching parameter on a beam velocity ratio, an interaction length, and an input drive power were analytically derived using a ballistic bunching theory. These theoretical analyses on the frequency-multiplying gyro-TWT were the basis of the experimental development. In the proof-of-principle experiment, the theoretical prediction of frequency multiplication from an X-band drive signal to a Ka-band output signal through the third harmonic electron cyclotron maser interaction in the two-stage tapered gyro-TWT was verified. The measured Ka-band output frequencies from 31.8 to 36.0 GHz were three times of the input drive frequencies from 10.6 to 12.0 GHz. The measured output power was about 20 dBm due to a reduced beam current of 160 mA. The power amplification, however, is expected when the beam emission is improved, and it is now underway.