Experimental results for a $1.5MW$⁠, $110GHz$ gyrotron oscillator with reduced mode competition

A new result from a $110GHz$ gyrotron at MIT is reported with an output power of $1.67MW$ and an efficiency of 42% when operated at $97kV$ and $41A$ for $3μs$ pulses in the $TE22,6$ mode. These results are a major improvement over results obtained with an earlier cavity design, which produced $1.43MW$ of power at 37% efficiency. These new results were obtained using a cavity with a reduced output taper angle and a lower ohmic loss when compared with the earlier cavity. The improved operation is shown experimentally to be the result of reduced mode competition from the nearby $TE19,7$ mode. The reduced mode competition agrees well with an analysis of the startup scenario based on starting current simulations. The present results should prove useful in planning long pulse and CW versions of the $110GHz$ gyrotron.