Profile modifications in PPCD experiments in RFX

In Reversed Field Pinch experiments, Pulse Poloidal Current Drive (PPCD) is an important tool to control magnetic and plasma profiles. The paper analyses the PPCD effect on the profiles of magnetic field, electron and impurity densities and electron temperature. From 3D MHD non-linear simulations a peaking of the parallel current profile during PPCD is found, associated to a significant reduction of the mode amplitude and magnetic fluctuations. The soft x-ray tomography shows a shrinking of the emissivity profiles, indicating an increased core temperature and again a central channeling of the current density. The hydrogen influx from the graphite wall, which dominates the discharge fuelling, is observed to decrease strongly at the toroidal region where MHD modes are locked. This explains why, despite the increased confinement associated to the higher temperature and lower magnetic fluctuations, the density does not increase. 1D transport analysis of PPCD shows that the current peaking in itself cannot explain the observed modification of the temperature profile: the core heat diffusivity has to be substantially decreased, consistently with the decrease of the magnetic fluctuations. (author)