Plasma-wall interaction: a complex combination of surface processes critical for thermo-nuclear fusion

Handling particle and heat loads on the plasma-facing in vessel components constitutes a major engineering problem in thermo-nuclear plasma devices. The choice of the plasma-facing materials is a crucial point in future devices, such as ITER (International Thermonuclear Experimental Reactor), which will determine the plasma facing components (PFCs) lifetime or the tritium (T) inventory build up in the vessel, which must be limited for safety reasons. In order to address the most critical issues, the European Task Force on Plasma Wall Interaction has been implemented in the frame of EFDA (European Fusion Agreement). The EU PWI TF brings together the efforts of 24 European associations in the following fields of investigation: Material erosion and transport in tokamaks Tritium inventory and removal techniques Transient heat loads on plasma facing components Dust production and removal techniques Associated modelling and diagnostic development This paper describes the organisation of the EU PWI TF. It provides examples for the multitude of surface processes involved, ranging from sputtering of PFCs by the plasma, to eroded material transport in the discharge, sticking of atoms and molecules on PFCs, and D/T trapping in the material. In particular, the present status of knowledge concerning material erosion and hydrogen retention for the choice of ITER materials (Beryllium, Carbon and Tungsten) is presented.