Diamond Windows for High Power Microwave Transmission

70540S02-II High power microwave gyrotrons, needed to initiate fusion reaction, require microwave extraction windows with high thermal conductivity, low microwave absorption, and low resistance to thermal cracking. Newly developed, diamond windows fabricated with Chemical Vapor Deposition (CVD) possess this combination of unique properties, but, thus far, CVD-diamond has proven to be an expensive and unreliable solution. This project will develop a new CVD deposition method that provides for higher growth rates to lower the window costs. Also, a non-destructive method will be developed for characterizing the diamond components to ensure reliability, both prior to and during operation in microwave-heated fusion and high power laser applications. Phase I demonstrated feasibility by the successful deposition of a two-inch-diameter diamond window, which met the specifications of the gyrotron manufacturer. An approach for developing a remote non-destructive technique to improve window reliability also was identified. In Phase II, the window deposition rate will be increased and the deposition area scaled up to enable greater than the 1MW microwave transmission required for initiating fusion. A non-destructive technique, based on the resonant ultrasound response of the window to laser excitation, will be established for the remote detection of the window¿s mechanical state, in order to warn of impending window failures. Commercial Applications and Other Benefits as described by awardee: In addition to fusion research, the new diamond windows should benefit industries involved with large scale industrial microwave heating; CO2 laser metal cutting; and microwave sources such as gyrotrons and traveling wave tubes used by both the civilian and military sectors.