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

The compatibility of the reversed field pinch configuration with a highly r adiative mantle at the edge has been proven by injecting neon into high den sity RFX plasmas: with respect to ordinary non-seeded discharges, energy co nfinement only marginally deteriorates, and the convection losses onto the plasma facing wall are reduced. Injection of neon into low density plasmas entails instead a significant increase of the effective charge and an incre ment of the ohmic input higher than the radiated power increase. The associ ated degradation of energy confinement tau (E) appears not to be peculiar t o impurity injection but follows a more general scaling with the heating po wer P-heat of the type re cc P-heat(-1). The radiation efficiency; defined as the ratio between radiated power and the impurity contribution to effect ive charge, is found to be 3 to 5 times higher than that in tokamaks. RITM simulations confirm the experimental findings.