Plasma Wall Interaction and Its Control by Wall Conditioning

Abstract

The surrounding material walls in fusion devices must fulfil three important tasks:provide high vacuum conditions necessary to provide clean fusion plasmasabsorb the power produced by the α-particles in the fusion processes and injected by auxiliary heatingenable the exhaust of the helium ash by thermalisation of the helium plasma ions on material surfaces in the vicinity of helium pumps.The interaction of the plasma with the surrounding wall surfaces (PSI: plasma surface interaction) is therefore a necessary condition for fusion devices and not to avoid. In the plasma wall interaction a variety of bulk material and surface processes are involved on one side together with various special processes in the near surface plasma region on the other side. They can modify the properties of the boundary and main plasma in a feed back like behaviour.1,2 A prominent example is the release of impurities from the walls by plasma particle impact which increases the energy loss of the plasma by radiation and reduces thereby the particle fluxes to and impurity release from the walls.