Locked modes induced plasma-wall interactions in RFX

In the RFX reversed field pinch (R = 2 m, n = 0.45 m) the plasma-wall interaction has been characterised in all of the discharges by the presence of the locking both in phase and in the laboratory frame of unstable MHD modes, These locked modes cause a helical deformation of the magnetic surfaces driving large power fluxes onto the wall. The plasma edge is severely perturbed: a power density loading as high as 100 MW m(-2) may locally be exceeded, the surface of the plasma facing components reach the sublimation temperature, the impurity release and the power radiated locally increase by a factor of similar to 100, large fluctuations in the electron density develop and halo currents flow in the inconel vacuum vessel. It is estimated that the locked modes are responsible for losses that may amount to up to about 30% of the total power input.