Two-stage Energy Recovery System for DEMO Gyrotron

The results of optimization of the two-stage energy recovery system for the gyrotron planned for use in the DEMO project are presented. The main attention is paid to the problem of spatial separation of electrons having different residual energy after interaction with the RF field. A separation mechanism with electron drift in weakly nonuniform electric and magnetic fields is chosen. To create such fields, a scheme with an azimuthal electric field between the first and second stages of the collector was used. It is shown that such a scheme makes it possible to achieve a sufficiently good spatial separation of energy fractions and thus obtain a full gyrotron efficiency of more than 70%.