Effect of gas pulses on transport in NBI plasmas of the TJ-II stellarator

Abstract

The experimental evolution of low-density (~1e19 m-3) NBI plasmas of the TJ-II Heliac-type stellarator in response to short gas-puff pulses is simulated with a transport model that includes elements for transport barrier formation, neoclassical radial electric field and the evolution of three carbon charge-states. Two typical phenomena following a gas pulse are described: the formation of pivot points in the emissivity profiles as a consequence of transport barrier formation processes, and the smooth confinement change due to changes in the neoclassical transport caused by the forced modification of plasma profiles.