Particle collection with the ergodic divertor of Tore Supra

For controlling the edge particle flux, a proposed method of pumping is to capture backscattered neutrals due to atomic processes with a dedicated vented structure. This solution has been tested with the ergodic divertor (ED) of Tore Supra. The investigated ranges of volume averaged density ?ne? and total power Ptot are (2.5-5.5)×1019 m-3 and 1-6.5 MW, respectively, covering both the high recycling and semidetached plasma regimes. In this domain of parameters, the neutral pressure in the ED plenum always remains proportional to the incident ion flux. It follows that the high recycling regime is the most efficient for density control. This regime is then studied in more detail and the behaviour of the edge temperature and density with ?ne? and Ptot characterized, together with the location of the transition towards the semidetached regime in the [?ne?×Ptot] plane. The particle balance around the neutralizers is analysed with the code EDCOLL (Ergodic Divertor COLLection), the simulations of which show a satisfactory agreement with both the pressure and Da emission measurements, demonstrating that both neutral recirculation and particle collection with the vented structure are correctly understood. Finally, possible improvements of particle control with the ED are discussed and the code EDCOLL is used to estimate the collection efficiency of an optimized structure. It is shown that the present performance could be multiplied by » 3, allowing efficient density control in the semidetached plasma regime at a moderate level of power.