ITER DIVERTOR RESEARCH-AND-DEVELOPMENT ACTIVITIES

One of the key challenges in designing the next generation tokamaks is the development of plasma facing components (PFC's) that can withstand the severe environmental conditions at the plasma edge. The most intensely loaded element of the PFC's is the divertor. The divertor must handle high fluxes of energetic plasma particles and electromagnetic radiation without excessive impurity build-up in the plasma core. It must also remove helium ash while recirculating a large fraction of the unburned hydrogen fuel so that vacuum pumping requirements are not excessive. The gas-dynamic mode of divertor operation proposed for ITER expands the divertor design window to include several alternate heat sink and armor materials that were not feasible for the previous high recycling divertor approach. In particular, beryllium armor can now be considered with copper, niobium or vanadium structural materials cooled by liquid metal or possibly helium in addition to water. This paper presents some of the results achieved under ongoing ITER Plasma Facing Components research and development tasks. The overall effort involves U.S. industry, universities and national laboratories and is directed towards developing and/or testing: (1) ductile beryllium and beryllium joining techniques; (2) prototype divertor component design, fabrication and testing; (3) fiber-reinforced composites for beryllium and carbon; (4) beryllium plasma spray processes; (5) compliant layers for PFC armor attachment; (6) sacrificial armor layers for the divertor end-plates; and (7) tritium permeation and inventory in proposed PFC materials and components. The paper focuses on work being conducted by the industrial support team consisting of McDonnell Douglas Aerospace, Ebasco, General Atomics, Rocketdyne, University of Illinois and Westinghouse.