Radiation and confinement properties of impurity seeded discharges in the reversed field pinch RFX

Abstract

The compatibility of the reversed field pinch configuration with a highly radiative mantleat the edge has been proven by injecting neon into high density RFX plasmas: with respectto ordinary non-seeded discharges, energy confinement only marginally deteriorates, andthe convection losses onto the plasma facing wall are reduced. Injection of neon into low densityplasmas entails instead a significant increase of the effective charge and anincrement of the ohmic input higher than the radiated power increase. The associateddegradation of energy confinement τE appears not to be peculiar to impurity injectionbut follows a more general scaling with the heating power Pheat of the type τE ∝ Pheat-1. Theradiation efficiency, defined as the ratio between radiated power and the impuritycontribution to effective charge, is found to be 3 to 5 times higher than that in tokamaks. RITM simulations confirm the experimental findings.