Incompressibility of impurity flows in low density TJ-II plasmas and comparison with neoclassical theory.

Poloidal and toroidal velocities of fully ionized carbon are measured by means of charge exchange recombination spectroscopy 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 n_e ≤ 10¹⁹ m^-3). Furthermore, comparison with neoclassical calculations shows quantitative agreement with the measured radial electric field and ion parallel mass flow in the absence of an external momentum input. [ABSTRACT FROM AUTHOR]