Helium injection plasmas in FTU

Abstract

In order to extend observations on the increase of electron density peaking in neon doped plasmas, already reported in FTU Mazzotta et al (2015 Nucl. Fusion 55 073027), some sessions have been performed by injecting helium gas on the L-mode plasmas during the last two experimental campaigns. This favorable scenario, which can fall within so called ‘highly radiative’ or ‘plasma detachment’ themes, is investigated in this paper. The description of the impact of the helium injection on plasma behavior, by varying plasma parameters and shape, is exposed, especially with respect to the density peaking and edge conditioning. It has been recorded that, not only the total amount of puffed helium, but also the injection rate intervenes in triggering a particle inflow. Finally, by using VUV spectroscopy measurements, a model to estimate concentrations of impurities is outlined here for the first time, in this way the helium amount is deduced.