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 ven ted structure. This solution has been tested with the ergodic divertor (ED) of Tore Supra. The investigated ranges of volume averaged density [n(e)] a nd total power P-tot are (2.5-5.5) x 10(19) m(-3) and 1-6.5 MW, respectivel y, covering both the high recycling and semidetached plasma regimes. In thi s domain of parameters, the neutral pressure in the ED plenum always remain s proportional to the incident ion flux. It follows that the high recycling regime is the most efficient for density control. This regime is then stud ied in more detail and the behaviour of the edge temperature and density wi th [n(e)] and P-tot characterized, together with the location of the transi tion towards the semidetached regime in the [[n(e)] x P-tot] plane. The par ticle balance around the neutralizers is analysed with the code EDCOLL (Erg odic Divertor COLLection), the simulations of which show a satisfactory agr eement with both the pressure and D-alpha emission measurements, demonstrat ing that both neutral recirculation and particle collection with the vented structure are correctly understood. Finally, possible improvements of part icle control with the ED are discussed and the code EDCOLL is used to estim ate the collection efficiency of an optimized structure. It is shown that t he present performance could be multiplied by approximate to 3, allowing ef ficient density control in the semidetached plasma regime at a moderate lev el of power.