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 Mi. 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 . The particle influx is significantly reduced and the particle confinement time scales . 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 Mi 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.