Operating the KIT 170 GHz 2 MW Coaxial-Cavity Gyrotron at 204 GHz: Performance Expectations and First Cold Test of the Quasi-Optical System - Ruess, T.; Avramidis, K. A.; Gantenbein, G.; Ioannidis, Z.; Illy, S.; Jin, J.; Lutz, F.C.; Pagonakis, I. G.; Ruess, S.; Rzesnick, T.; Thumm, M.; Wagner, D.; et al. (2019 International Vacuum Electronics Conference, IVEC 2019, 2019)