Incompressibility of Impurity Flows in Low Density TJ-II Plasmas and Comparison with Neoclassical Theory

TL;DR

This study measures impurity flow velocities in TJ-II plasmas, demonstrating flow incompressibility and agreement with neoclassical theory, specifically matching the radial electric field and bootstrap flow without external momentum input.

Contribution

It provides a detailed analysis of impurity flow incompressibility in low density TJ-II plasmas and compares measurements with neoclassical predictions, confirming theoretical models.

Findings

Flow measurements are compatible with incompressibility.

Quantitative agreement with neoclassical calculations.

No external momentum input needed for observed flows.

Abstract

Poloidal and toroidal velocities of fully-ionised carbon are measured by means of charge exchange recombination spectroscopy (CXRS) in the TJ-II stellarator. We present a detailed treatment of the 3D geometry and show that flow measurements, performed at different locations of the same flux surface, are compatible with flow incompressibility for the low density plasmas under study (line averaged electron densities $\bar{n}_e\,\le\,10^{19}$ m$^{-3}$). Furthermore, comparison with neoclassical calculations shows quantitative agreement with the measured radial electric field and ion bootstrap parallel flow in the absence of an external momentum input.