High density limit in reversed field pinches

The fusion triple product depends on density, which is therefore a key parameter for the future fusion reactor. In this paper the high density limit is studied in the reversed field experiment (RFX-mod) device in Padova, Italy. A rather complete experimental picture of the high density regimes is provided, showing a series of features, such as, plasma flow inversion in the edge, density accumulation, radiation condensation (poloidally symmetric and toroidal asymmetric) which resemble the MARFE phenomenon characteristic of tokamak discharges. However, in RFX-mod high density does not cause a disruption, as often observed in tokamaks, but a soft landing of the plasma current. According to a new 1D transport/radiative code applied to analyze the high density discharges, the current decay is due to an increased need for dynamo in these highly resistive, edge-cooled discharges. The relation between the radiative pattern of RFX-mod high density plasmas, the magnetic topology, and edge radial electric field is discussed.