Effect of power reflection on the operation of a low-Q 8 GHz gyrotron

The operating characteristics of a low-Q (Q/sub cav/=225), 8-GHz gyrotron oscillator operating in the TE/sub 011//sup O/ mode and submitted to various mismatched loads are reported. Under matched conditions, output power up to 310 kW ( eta =35%) and maximum efficiency up to 43% were measured. In general, power reflection from loads with different phases and amplitudes leads to an output power decrease. Excessive reflections cause mode switching (TE/sub 011//sup O/ to TE/sub 012//sup O/) or even arcing inside the tube. The effect of power reflection is seen to increase rapidly with current and output power. Nevertheless, as predicted by calculations, the maximum output power is not reached under matched conditions but with a specific nonzero value of the complex reflection coefficient.< >