Comparisons of Electron Temperature and Density, and Ion Temperature Profiles in the TJ-II Stellarator

Abstract

Charge exchange-neutral particle analyzer diagnostics are used to obtain majority ion temperature profiles for plasmas created in the TJ-II stellarator. However, because of technical limitations, measurements are limited to two radial positions per discharge. Therefore plasma reproducibility for a large number of discharges is essential for performing scans across the plasma minor radius and hence for obtaining ion temperature profiles. Such conditions have recently been achieved in the TJ-II by the implementation of a lithium wall coating which has significantly facilitated this task. In this paper, ion temperature profiles obtained under electron cyclotron resonance (ECR) and neutral beam injection (NBI) plasma heating conditions are compared with electron temperature and density profiles obtained using a Thomson Scattering diagnostic. From this, similarities in the forms of the ion temperature and electron density profiles are noted for ECR heated plasmas whilst for NBI heated plasmas similarities are observed between ion temperature and electron temperature profiles. Finally, after explaining the different behaviours of the profiles in terms of ion power absorption profile, we demonstrate the possibility of determining ion temperature profiles using two localized ion temperature measurements plus Thomson Scattering profiles.