Advanced Output Coupling for High Power Gyrotrons

Current high power gyrotrons are restricted to single frequency operation with output in a Gaussian quasi-optical mode. The output requires an expensive Mirror Optical Unit (MOU) to couple the quasi-optical RF beam into corrugated waveguide. This adds approximately $500,000 to the system cost. This program is employing an innovative technique to couple RF power directly into corrugated waveguide inside the gyrotron. This reduces the diameter of the RF beam and allows implementation of a Brewster angle window. It also eliminates the requirement for an MOU, saving users approximately $500,000 per gyrotron. The operation of the direct coupler was confirmed by low power testing during the Phase I pro- gram. A Brewster window was designed, built, and successfully tested. The program initiated an upgrade to the computational tools to increase the bandwidth of the direct coupler. Upgrade of the design codes will be completed and a broadband coupler built for high power testing. The coupler will be initially tested in the experimental gyrotron at MIT. The Brewster angle window will be initially tested with the MIT gyrotron, and then tested at high average power using a gyrotron at General Atomics.Commercial Applications and Other Benefits: High power RF sources are desired for improved heating and instability suppression in most all tokamak devices. If successfully developed, this coupler and window would likely be implemented in all future, high power, gyrotrons in the U.S., Europe, and Asia. This would reestablish the U.S. as the leader in high power gyrotron technology.