Second harmonic-multiplying gyrotron
traveling -wave amplifier
The second harmonic TE02 gyrotron traveling wave amplifier (gyro-TWT)
is a high-power, broadband, millimeter-wave amplifier with a low applied
magnetic field. A multi-stage gyro-TWT design with lossy section,
severed section and mode-selective circuit is proposed to stabilize the
amplification. This study presents a nonlinear analysis of typical
oscillations, including absolute instability and gyrotron backward
oscillation (gyro-BWO). The multi-stage gyro-TWT seem to increase
effectively the start-oscillation currents of the absolute instability and
gyro-BWO. The multi-stage gyro-TWT is predicted to yield a peak output
power of ~330 kW at 180 GHz, a saturated gain of ~70 dB and a
bandwidth of 5.0 GHz for a 100 kV, 15 A electron beam with an axial
velocity spread Δvz/vz=5%. Meanwhile, a mode-selective circuit with a
transverse sliced interaction structure is employed for suppressing
absolute instabilities in the gyro-TWA. Since the wall surface current for
the TE0n mode is in the azimuthal direction, the TE01 and TE02 waves are
almost unaffected as it travels through the transverse slice. In contrast, the
competing modes with axial surface currents are significantly affected.