A 350 GHz, 1 MW Class Gyrotron for Commercial Fusion Reactors

As we make progress in the design and fabrication of ITER experimental fusion reactor there is new focus on the next generation commercial fusion reactors. Several design concepts have been put forward including the DEMOnstration power station followed by the PROTOtype power station and other concepts for compact reactors. Electron Cyclotron Resonance Heating (ECRH) and Electron Cyclotron Current Drive (ECCD) will be vital tools in all these reactors both for plasma control and heating. Based on the preliminary designs most of these reactors will require 20 – 40 MW of power in the 250 – 350 GHz range (depending on chosen magnetic field) for ECRH and ECCD. This power will be delivered by a bank of gyrotrons each with a minimum of 0.5 MW continuous wave output with a desired goal of 1 MW to reduce the number of devices. We propose to develop a 1 MW, 350 GHz gyrotron for use in future commercial fusion reactors. The gyrotron will use a novel mode selective cavity to allow stable operation in the higher order modes. It will use a multi-stage depressed collector to achieve an overall efficiency > 65 % and in the process improve the reliability of the collector by reducing the thermal dissipation. We propose to use hypervapotron cooling based on subcritical boiling to improve heat extraction and create a compact system for large scale deployment. We propose to fabricate key parts of the gyrotron using Additive Manufacturing to reduce the time and cost of part fabrication achieved by minimizing the number of joints and other machining operations. The proposed system will advance the state-of-the-art significantly and pave the way for successful adoption of such compact systems in commercial reactors. In Phase I, we propose to present a complete design of a 1 MW, 350 GHz gyrotron using benchmarked state-of-the- art design tools such as Michelle for electron gun and collector design and MAGY for cavity design. A complete thermal model of the advanced depressed collector will be performed using Ansys Mechanical and Computational Fluid Dynamics tools. In a future Phase II project, we propose to build a short pulse prototype (design capable of continuous wave operation) to demonstrate they key physics design of stable operation at millisecond long pulses and achieve a total efficiency in excess of 65%. This successful demonstration of the key physics and engineering aspects will pave the way for the fabrication and testing of a continuous wave device with funding support from a sponsor.