Coaxial multistage depressed collector design for high power gyrotrons based on E×B concept

The gyrotron operational efficiency is considered as a very important factor of future fusion power plants. The development of an efficient multistage depressed collector (MDC) for the annular spent electron beam is the key for a significant increase in the operational efficiency. To achieve this target, a systematic investigation of all kinds of possible design approaches was conducted during the last decade at the Karlsruhe Institute of Technology. A promising approach using a cylindrical hollow collector design was found. In this work, another generic design approach based on the E × B drift concept for the spent electron beam is presented which uses a coaxial collector design. This new generic approach offers a significant improvement in the collector efficiency. Even more, it opens the path for the design of a large variety of new MDC collectors with different characteristics, e.g., the number of stages and the wall geometry.