Numerical Investigation on Spent Beam Deceleration Schemes for Depressed Collector of a High-Power Gyrotron - Pagonakis, Ioannis Gr.; Illy, Stefan; Ioannidis, Zisis C.; Rzesnicki, Tomasz; Avramidis, Konstantinos A.; Gantenbein, Gerd; Kobarg, Thorsten; Piosczyk, Bernhard; Thumm, Manfred; Jelonnek, John (IEEE Transactions on Electron Devices, 2018)