Investigation on mode eigenvalue limits for stable 236 GHz, 1 MW-class gyrotron operation

In order to find the upper limit for mode eigenvalues for stable 1 MW-class gyrotron operation, the behavior of a 236 GHz cylindrical (hollow) cavity gyrotron design is theoretically analyzed for operation with even higher order modes (eigenvalues between 100 and 145). In this frame, two independent methods are used to determine the effect of neighboring modes on mode stability and to estimate the eigenvalue limit for stable operation. With consideration of realistic electron beam parameters (velocity spread and beam width) and a diode start-up regime, the results of both methods suggest that mode eigenvalues smaller than 125 should be selected to ensure the stability of operation.