Thermal mechanical analysis of novel electron collector for megawatt class gyrotrons

Electron Cyclotron Resonance Heating (ECRH) is a key technology necessary for plasma heating, magnetohydrodynamic (MHD) instability control such as those from Neoclassical Tearing Modes (NTM) and for EC assisted startup in Tokamaks. Currently, gyrotrons are the only proven vacuum tube technology that can generate sufficient power in continuous wave operation at the frequency of ∼350 GHz needed for next generation fusion devices. As a proof of concept, analysis of a 225 GHz, 1 MW gyrotron is being pursued. High frequency gyrotrons operate with high order cavity modes and the design limit for thermal loading on the cavity walls is currently ∼3 kW/cm2. The ohmic heat load on the cavity increases quadratically with frequency. Hence, advanced heat removal techniques will allow operation at higher frequencies without the need for going to extremely high order modes that bring increased risk of mode competition. Here we will present a novel additively manufactured (AM) electron collector and analysis of life enhancing concepts including non-cylindrical cooling channels, helical cooling channels, segmented hot wall, and electron beam sweeping to increase the heat removal from the collector. Implementation of these concepts can lead to >50% reduction in maximum stress in the collector, thus increasing the life of the collector. The choice of AM for fabrication presents opportunities for incorporating these unique geometries in a cost effective, monolithic geometry that eliminates complex joining and machining and reduces part count. We will present our studies of AM collector geometries based on GRCop-42 alloy. This is a promising path for reducing the size of the device and thus the overall cost of the system.