Gyrotrons are used for electron cyclotron resonance heating as well as for non-inductive current drive in fusion experimental reactors. The gyrotron operational efficiency is considered as a very important factor for 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 electron 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. For that reason, 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 [1-6]. 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 high collector efficiency. ... mehrThe outcome of this study is a variety of MDC designs with different characteristics, such as the number of stages, the wall geometry, etc. In addition, the development of anMDC prototype for a high power gyrotron based on E×B drift concept is in progress. In the design of such a prototype, several technical questions are under investigation, such as the high voltage isolation, the cooling of subcomponents, the mechanical stability of the construction, etc.
Details of this work will be presented while the opportunity to exchange knowledge and experiences with other participants on the design elements of gyrotron collectors will be opened.