Influence of biased electrode on plasma confinement in the Tohoku University Heliac

Observations of an increase in electron density triggered by electrode biasing are reported in the Tohoku University Heliac (TU-Heliac). The biased electrode, which is located deep inside the plasma, induces a strong positive radial electric field, after which the line density increases by a factor of 2, the electron density profile steepens and the fluctuation level drops. We estimate the damping force opposing poloidal rotation experimentally and compare it with various versions of the neoclassical theory. The experimental results agree in that the measured damping force has a local maxima at |MP| = 1-2 and tends to be proportional to M_p in the high speed region (|M_P| > 3-6), where M_p is the poloidal Mach number. For |M_p| < 1-2, however, the dependence of the measured damping force on M_p differs a little from theoretical predictions.