Direct Coupled Gyrotrons for Plasma Heating

High power gyrotrons typically produce RF power in a ${HE}_{11}$ waveguide inside the vacuum. The direct coupler was Gaussian free-space mode. An internal converter transforms the integrated into the 110 GHz, 1 MW, short pulse gyrotron at MIT, whispering gallery mode from the cavity to a Gaussian beam using a shown in Fig. 1. Tests indicated that the gyrotron produced the quasi-optical launcher and a series of mirrors. Transmission of this same output power and efficiency as the conventional Gaussian power typically requires transformation into an ${HE}_{11}$ mode in corrugated waveguide. This conversion is achieved using a Mirror Optical Unit, which uses a second series of mirrors. The transformation of the whispering gallery mode to a Gaussian beam and then to an ${HE}_{11}$ mode requires a complexity of RF structures, increasing cost and RF losses. This program is developing a coupler that transforms the whispering gallery mode directly into an ${HE}_{11}$ mode inside the gyrotron. This results in significant reduction in gyrotron cost and RF losses and eliminates the Mirror Optical Unit.