The isotope effect in the RFX-mod experiment

The isotope effect in the reversed field pinch magnetic configuration is investigated for the first time comparing hydrogen and deuterium plasmas of the RFX-mod experiment. The picture which emerges has several similarities with the results of tokamak experiments, since plasma properties improve increasing the isotope mass M-i. The electron temperature is higher in deuterium than in hydrogen in a large fraction of the plasma volume (r/a<0.9) and the energy confinement time scales similar to M-i(0.3). The particle influx is significantly reduced and the particle confinement time scales similar to M-i(0.45). The effect on confinement is mainly due to the mitigation of transport at the edge, internally to the scrape-off layer where long range correlations have been detected. Moreover a modification of magnetohydrodynamic properties is observed. Increasing M-i brings about a stabilizing effect on tearing modes, and increases the tendency of plasma to produce quasi-single helicity, which becomes longer, purer and more resilient to weak sawtoothing. Finally, the dynamo process that sustains the magnetic configuration becomes more discrete.