First Experiments on Multistage Energy Recovery in a 4-mm Wavelength Gyrotron

A novel type of multistage depressed collector has been manufactured and tested in the experiments with a 4-mm wavelength gyrotron. First experimental results showing an overall efficiency of
$\sim \; 70$
% for the 4-stage scheme and of
$\sim \; 72$
% for the 5-stage scheme with an output power of about 100 kW are presented. The possibility to increase the gyrotron overall efficiency is discussed.