Performance of brazed graphite, carbon-fiber composite, and TZM materials for actively cooled structures. Qulification tests

The divertor of a near-term fusion device has to withstand high heat fluxes, heat shocks, and erosion caused by the plasma. Furthermore, it has to be maintainable through remote techniques. Above all, a good heat removal capability across the interface (low-Z armor/heat sink) plus overall integrity after many operational cycles are needed. To meet all these requirements, an active metal brazing technique is applied to bond graphite and carbon-fiber composite materials to a heat sink consisting of a Mo-41Re coolant tube through a TZM body. Plain brazed graphite and TZM tiles are tested for their fusion-relevant properties. The interfaces appear undamaged after thermal cycling when the melting point of the braze joint is not exceeded and when the graphite armor is >4 mm thick. High heat flu tests are performed on three actively cooled divertor targets. The braze joints show no sign of failure after exposure to thermal loads approximately 25% higher than the design value surface heat flux of 10 MW/m².