Tore Supra divertor screening efficiency during density regime experiments

Abstract

The Tore Supra ergodic divertor (ED) screening efficiency has been investigated in density regime experiments. The ED screening efficiency is analysed by using the `tightness' concept, which is the ratio of the density on the ED neutraliser plates to the volume averaged plasma density. Tightness is studied as a function of different plasma edge parameters, such as T div, ED magnetic perturbation ( Δ), plasma composition, location of recycling source, and additional power. Tightness is shown to increase with Δ, P div 0.55/(1− Fr) 1.22 , and 1/ T div 0.5. These trends are well explained by a simple 0-D model, where the particle confinement time in the ergodized peripheral region is very small. Finally, tightness increases with the power conducted onto the ED plates. Since ED plasmas have low P div, their tightness value remains low compared to that obtained with axisymmetric divertors for which P div is considerably larger. Increasing P div will result in an improved tightness and a better particle control.