Linear microstability investigation of a Neon impurity seeded FTU plasma

Seeding of Neon impurity in FTU ohmic plasmas causes a spontaneous increase of line averaged electron density up to a factor two (notwithstanding the absence of Deuterium gas puffing) associated with a significant increase of the peaking factor [1]. These effects, previously studied in the so called RI mode, have to be further investigated in particular by deepening the impurity related transport mechanisms, both to describe their role in the on-axis density increase, and to evaluate the seeding to be used to increase radiation in the divertor, while avoiding the risk of core plasma contamination [2]. As for particle transport and the microturbolence analysis, first results lead to relate the mechanism of density peaking to the ITG growth rate, as calculated by Gyro-Kinetic codes. In order to assess the role of the ITG growth rate, a detailed linear micro-stability analysis of a Neon doped pulse has been carried out with the gyro-kinetic code GKW, and compared with a reference undoped pulse at the same line-average electron density and set plasma parameters. The doped discharge has higher ion and electron gradients after the Neon injection (consequently higher ITG and ETG modes) than the undoped one taken at the same line averaged density. Further simulations take into account the impurity profiles as reconstructed by an impurity transport code [3]. The presence and the peaking of the Neon impurity reconstructed profile plays an important role on the presence of unstable modes.