2019 Status on the design of the EU/KIT TE34,19-mode coaxial-cavity gyrotron towards dual-frequency 170/204 GHz operation

Fusion gyrotrons for DEMO and future Fusion Power Plants (FPP) will require multi-megawatt continuous-wave (CW) operation at multiple possible frequencies for Electron Cyclotron Resonance Heating and Current Drive (EC H&CD). Currently, for the gyrotron R&D it is assumed that the operating frequencies will start from 170 GHz (ITER) and will move up to a maximum of 240 GHz.
The existing 170 GHz 2 MW TE34,19-mode coaxial-cavity modular short-pulse (SP) pre-prototype gyrotron was modified to verify the coaxial-cavity technology at long pulses. It is accompanied by a theoretical investigation of a possible upgrade of the existing tube towards the operation at higher frequencies using the new 10.5 T super-conducting (SC) magnet of the FULGOR gyrotron test stand. The target is a first of its kind operation of the coaxial-cavity pre-prototype at 204 GHz and at 236 GHz. In initial simulations, it has already been verified, that the operation at 204 GHz requires a slight modification of the interaction cavity and an enlargement of the tube. Taking the modifications into account the predicted RF output powers are 2.63/2.04 MW and the interaction efficiency are 37.8/34.5 % at operating frequencies of 170/204 GHz, respectively. ... mehrCurrently, the operating parameters for the MIG are under investigation. Further, the quasi-optical system was optimized to allow multi-frequency operation.
Finally, in frame of this work, there are a significant upgrades of the existing measurements tools ongoing. The two major upgrades are, firstly, the proper excitation of very high order modes using an advanced mode generator, and, secondly, the upgrade of the existing frequency measurements system towards 240 GHz. Additionally, to the simulation results for the modified KIT coaxial-cavity pre-prototype gyrotron, the status on the upgrades of the measurements tools are presented therefore.