Density control and plasma wall interaction in Tore Supra

摘要

Control of recycling fluxes is needed for density control. The walls are the major source of particles around the plasma and they are the key of density control. Different walls are involved during plasma operation. Walls far from plasma desorb water if heated during operation. In future tokamak as in Tore Supra Upgrade (CIEL), temperature around the vessel will be controlled to avoid such a behaviour. One can also modify walls physical and chemical properties to reduce water inventory and/or prevent water desorption. Walls in direct interaction with plasma trap plasma particles and can be saturated. Some experiments exist to study such saturation behaviour but extrapolation to reactor is not possible. In Tore Supra, no evidence of wall saturation is observed during long discharge operation which are done at low plasma density. Conditioning plays an important role to reduce wall particle trapping and wall saturation status. New conditioning procedure are actually under development for next step deviceswhich are operating with permanent toroidal field. At Tore Supra, ICRH conditioning and repetitive plasma breakdown have proven to be efficient. At the same time, new measurements are used to estimated in real time what is the wall saturation status. They are needed to get a reproducible start-up conditions for tokamak operation. Ad last, walls are remainig which are not treated by helium glow discharge for instance. They are playing an important role to particle trapping and tritium inventory. Even if some new procedure as oxygen flushing are used presently, new methods must be developed in the future to control this wall particle trapping.