Launching Loss in the Reflection Wideband Gyrotron Travelling Wave Amplifier (Gyro — Twt)

Experiments(1) show that the usual 9 db launching loss is absent in the recently proposed wide-band gyro-twt(2). In the experiment, an input signal is injected from the downstream of the electron beam inside a mildly tapered waveguide. Upon reflection at cutoff, the signal co-propagates with the beam and is amplified. By analyzing the reflection process in detail, we found that the gentle taper of the waveguide produces minimal mode conversion and hence insignificant loss, in agreement with experiments(1). Beam prebunching is also found to be relatively unimportant.