Density control in Tore Supra with ergodic divertor and multi-pellet injection

A large part of the experimental programme of TORE SUPRA has been devoted to ohmic plasmas studies in many configurations. These experiments were restricted as far as the particle content is concerned by the 'density limit'. This limit appears to be a strong function of the ionic species, the fuelling method and the plasma edge characteristics. Typical examples of this are shown in ergodic divertor and multi-pellet experiments. The experimental procedures such as different type of gas and pellet injection during the ergodic divertor pulse are described in the next section : the fuelling efficiency is reduced if the edge deconfinement produced by the ergodic divertor is accompanied by some pumping by the wall. At the same time, the high-recycling zone behaves like a radiating layer, especially since it becomes cooler with ergodization. The simultaneous use of pellet injection and edge field lines ergodization should yield a convenient way to control both plasma density and radiative losses. (author) 8 refs., 2 figs