Initial Investigation on Diffractive-Wave Feedback Mechanism of Confocal Gyro-TWAs

In this letter, diffractive-wave feedback mechanism of confocal gyrotron travelling-wave amplifiers (gyro-TWAs) is presented and verified in cold-test experiments for the first time. The reason for this physical mechanism is that part of the diffractive wave re-enters the open circuit during outward radiation. The achieved circuit loss is less than the theoretical predictions without considering the feedback. This abnormal behavior will seriously deteriorate the stability of the amplifiers including potential near-cutoff instability and backward-wave oscillation, presenting as a main factor that greatly degrades the performance of confocal gyro-TWAs, especially in high-gain operation.