Description
Survival of extreme heat fluxes is one of the central technological challenges for practical thermonuclear fusion reactors. Present estimates for future fusion devices predict steady-state heat loads of 10 – 20 MW/m², yet uncertainties in predicted values highlight the need for next-generation plasma-facing components (PFCs) capable of withstanding potentially much higher loads.
At the IPP Prague we are developing a heat-shield prototype based on a novel STEAM (Super-Thermal Exchange via Advanced Micro-boiling) technology. The concept employs jet-impingement cooling within a copper structure, maximizing water phase change while ensuring directed vapor expulsion. This approach mitigates vapor-induced limitations and substantially raises the critical heat flux (CHF) threshold above 100 MW/m².
The heat-sink prototype, currently at Technology Readiness Level 3-4, has been tested on a 110 kW plasma torch using 3 – 30 s cyclic pulses. It sustained peak heat flux of 80 MW/m² undamaged for a cumulative 20 minutes. With an optimized water injector, survived peak heat-flux rose up to 160 ± 30 MW/m² during a cumulative 1 min test without damage — representing the most intensive non-destructive macroscopic heat shield test reported to date.
Heat-flux measurements are obtained via IR thermography using a graphite reference target, since the low-emissivity copper-alloy STEAM surface cannot be directly observed. The target’s temperature distribution is fitted to forward heat-transfer simulations to reconstruct the heat-flux profile.
The STEAM concept is potentially suited for cooling of localized regions a few centimetres wide, such as tokamak strike points or gyrotron cavities. For reactor integration, the copper cooler would need a protective tungsten or liquid-metal layer, whose thickness and surface temperature limits may reduce overall cooling efficiency. Nonetheless, the demonstrated performance indicates STEAM as a promising pathway for managing reactor-relevant heat loads.