Record heat shield against steady-state heat flux 100 MW/m² (not only) for tokamaks

Abstract Effectively withstanding the extreme surface heat fluxes, possibly exceeding the limit 20 MW/m² of the best nowadays shields, continues to pose one of the last few major unresolved engineering challenges for a practical thermonuclear fusion reactor. We present a novel STEAM heat shield aimed for a tokamak or stellarator divertors and potentially applicable also in microwave gyrotrons, high power microelectronics or solid rocket combustion chambers. It employs high-speed liquid impingement cooling, developed and systematically validated under extreme heat flux conditions. The design facilitates efficient boiling-driven heat removal. It is tested on a plasma torch, supported by heat transfer simulations, infrared thermography and calorimetry. Our shield sustained for over 20 minutes a steady-state heat flux of 73 MW/m² (31 kW across 4.2 cm²), exceeding conditions on the Sun. Fast camera revealed a strongly boiling outlet of an open water circuit and shape-optimized water injector. Even more, exactly where thermovision indirectly indicated that most liquid changes phase into steam, the STEAM survived for 1 minute under heat flux reaching 130 MW/m² — representing the most intensive sustained non-destructive heat shield test ever reported.