Towards Realistic Experimental Conditions for Validation of Effective Resonator Cooling in Multi-MW CW Gyrotrons

Efficient cooling of high-power gyrotron resonators is essential for Electron Cyclotron Resonance Heating and Current Drive (ECRH & CD) systems in fusion experiments, where intense ohmic load (~2 kW/cm2) can cause thermal deformation, impacting performance and efficiency. While conventional European gyrotrons use Raschig rings (RR) cooling, mini-channels (MC) cooling offers superior thermal management, particularly for the 2 MW coaxial longer pulse gyrotron. Experimental campaigns at the Karlsruhe Institute of Technology (KIT) are based on the use of induction heating as heat source and focused on advancing MC cooling performance and testing fabrication methods, including metallic 3D printing additive technique. Calorimetric and cooling tests on a 3D-printed copper mock-up demonstrated comparable performance to conventionally manufactured designs but revealed a ~40% higher pressure drop due to surface roughness, highlighting the need for further optimization for vacuum applications. A major experimental goal was increasing the applied thermal flux to approach real gyrotron operational levels. To achieve this, two high-power induction heating devices were integrated into the test setup. ... mehrThese upgrades allowed for induced thermal loads over six times higher than in previous experiments. Maximum applied heating power reached 41.5 kW, achieving heat fluxes up 1 kW/cm2 based on detailed 3D electromagnetic simulations. Additionally, a vertical mechanical support was developed to improve experimental accuracy by enhancing coolant flow symmetry and replicating the typical gyrotron installation orientation. Those advancements mark a significant step toward experimentally validating advanced cooling concepts under conditions approaching real multi-MW-class gyrotron operation. Ongoing work will further refine the setup and support advanced numerical modeling, aiding the development of optimized cavity cooling solutions for future fusion applications.