Direct Coupled Gyrotrons for Plasma Heating

Current high power gyrotrons for plasma heating use an internal launcher and multiple mirrors to generate a Gaussian output beam that exits the tube through a large diamond window. A Mirror Optical Unit (MOU) external to the gyrotron is required to transition the Gaussian beam into an HE11 mode in corrugated waveguide for transmission to tokamaks. The internal mirrors and large diamond window costs approximately $200K. The MOU costs approximately $350K to build with additional cost of $250K per year from lost RF power. A more cost effective and efficient approach is required for transitioning gyrotron power into transmission lines. Calabazas Creek Research Inc. (CCR) is proposing to transition the gyrotron RF power into corrugated waveguide inside the tube using an internal (direct) coupler. This eliminates internal mirrors costing approximately $80K and reduces the diamond window cost by approximately $100K. It also eliminates the MOU and its associated cost. The Phase I program will design, build, and test at low power a direct coupler for a MW-class, long-pulse gyrotron. The program will also design a compatible diamond output window and hardware to interface the coupler to an existing gyrotron. A complete design will be generated for installing the coupler into a gyrotron and testing at full power in the Phase II program.