Towards the Realization of a Multistage Depressed Collector Based on E×B Drift

Gyrotrons are used for plasma heating at the electron cyclotron resonance or its harmonics as well as for current drive to operate a fusion reactor. The gyrotron operational efficiency is considered as a very important factor for the future fusion power plants. Single-stage depressed collectors have been successfully used in gyrotrons. The key of a significant increase of the gyrotron efficiency is the development of an efficient multistage depressed collector (MDC) for the annular spent gyrotron beam. The design of an MDC system for gyrotrons is not trivial due to the fact that the spent electron beam is confined by a relatively strong magnetic field in the collector region. Therefore, the electrostatic sorting used in TWT and klystron MDCs is not applicable to the spent electron beam in gyrotrons. The separation of the spent beam electrons of a high power gyrotron based on the E×B drift concept was proposed in 2008 and is considered as the most promising method. Based on this concept, a systematic investigation of many design approaches with E×B drift has been conducted during the last years. In this work, a plurality of different designs is presented that produce an azimuthal electric field by a helical gap to separate the spent electron beam in order to achieve a high collector efficiency. ... mehrThe outcome of this study is a large variety of MDC designs with different characteristics, such as the number of stages, the wall geometry, etc.