Experimental study of DEMO helium cooled divertor target mock-ups to estimate their thermal and pumping efficiencies

The helium cooled divertor for the DEMO fusion reactor is designed for removal of surface high-heat-flux up to 15 MW/m2 during normal operation. To reduce thermal stresses in divertor plates finger-like array structure was chosen, where each tungsten finger is cooled by helium at inlet parameters of 10 MPa, 634 °C. The gas puffing facility (GPF) was developed for measurement of mock-ups performance at the reversed high heat flux, when the plasma-facing surface of finger-like mock-up was intensively cooled by water. The goals of these experiments are: (1) to compare heat removal performance for different design mock-ups and (2) to adjust computational fluids dynamics (CFD) codes for accurate simulations. Long helium pulses (∼100 s duration) and sufficient capability (1-2 kg of He per pulse) facilitate attainment of the steady-state regime in experiments, when 5-15 g/s mass flow rate of helium was scanned. Results of last experimental campaign carried on in December 2004 revealed that all helium distributing cartridge options demonstrate optimistic performance (as compared to CFD simulations) and capability to transfer 10-25 MW/m2 in the helium mass flow rate (MFR) range of 5-15 g/s.