SBIR-STTR Award

Step-tunable gyrotrons are desired for electron cyclotron heating and suppression of instabilities in tokamak fusion plasmas. High power tunable gyrotrons are in development in various countrie; however, attempts to develop a high power, broadband vacuum window to transmit the power have been unsuccessful. CVD diamond appears to be the only material capable of transmitting the 1 MW CW power required. Implementation of diamond windows in the current gyrotron configuration is impractical due to window size and cost issued. Calabazas Creek Research, Inc. recently developed an innovative technique for converting RF power inside the gyrotron directly into HE11 waveguide. This reduces the diameter of the RF beam and allows implementation of a Brewster angle window. The size of the diamond material required is comparable to that of existing windows for single frequency gyrotrons. 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, these windows would likely be implemented in all future, high power, step-tunable gyrotron in the U.S., Europe, and Asia

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.