Impurity screening in the RFX reversed field pinch

Despite the large input power of tens of MW, in the reversed field pinch RF X, the effective charge can be remarkably small. Z(eff) decreases with dens ity but does not show a dependence on the plasma current up to 1 MA for a g iven density. It is found that due to the large total particle outflux (2 x 10(23) s(-1)) the energy per particle is kept within reasonable levels. Th ese values, together with the carbon yield and ultimately the impurity conc entrations, are comparable with the tokamak case, where typically both powe r input and particle outflux are proportionally lower by an order of magnit ude. Experimental results and Monte Carlo simulations suggest that in RFX t he particle screening is due to the short ionisation length of neutrals wit h a contribution of the finite Larmor radius effect. (C) 1999 Elsevier Scie nce B.V. All rights reserved.