Experimental results for a 1.5 MW, 110 GHz gyrotron with an improved cavity

Recently, a cavity (named V-2005) has been designed and successfully tested for the 1.5 MW, 110 GHz gyrotron experiment at MIT. The novel feature of the cavity lies in its low diffractive Q factor which corresponds to reducing the Ohmic loss on the cavity wall. The design and mode competition analysis were done with the simulation code, MAGY. In short pulse experiments, we achieved 1.67 MW of output power with an efficiency of 42 % at 97 kV of beam voltage and 41 A of current. Compared to the previous cavity (named V-2003), the new cavity has a smaller output taper angle and the Ohmic loss has been reduced by 25 %. The experimental result shows an increase in efficiency (42 % vs. 37 %) in the new cavity compared to the previous one. A map of the observed modes was generated by varying the cathode and cavity magnetic fields for both cavities. Less competition from the TE_19.7 mode was observed in the V-2005 cavity.