PT Unknown AU Ruess, T Avramidis, KA Gantenbein, G Illy, S Rzesnicki, T Thumm, M Jelonnek, J TI Theoretical Study on the Possibility for Stepwise Tuning of the Frequency of the KIT 2MW 170/204 GHz Coaxial-Cavity Gyrotron PY 2020 LA english ER