Impur ity behaviour and r adiation patter n in the RFX-mod r ever sed field pinch

Intr oduction RFX-mod is the largest reversed field pinch operating nowadays, with 2 m in major radius, 0.459 m in minor radius and an installed power dimensioned to drive up to 2 MA of plasma current. In the long shutdown period completed at the end of 2004, several new features have been introduced. Above all, a closer resistive shell with external saddle coils has been installed to harness the rich spectrum of MHD modes. This paper describes the behaviour of the impurities in discharges with plasma current of about 600 kA, in terms of influxes from the wall, radiated power and effective charge; first results on the impurity toroidal velocity are also presented. In the former machine configuration, impurities did not represent a major problem. Despite the strong plasma wall interactions the effective charge was kept at reasonable levels (i.e. below 2), especially at high density. In this respect first observations on the restarted machine confirm the trend. In fact, the measured effective charge towards the plasma density is comparable or slightly lower than what found in the former machine. The effect on the influxes and on the emitted radiation of the strong poloidal and toroidal asymmetries associated with the plasma horizontal shift and with the wallmode locking have been investigated. Results and discussion The TV camera pictures of the inner wall in 600kA discharges show strong plasma wall interactions (PWI) in the region where the phase locked MHD modes form a local deformation in the plasma column (se