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 in creases by a factor of 2, the electron density profile steepens and th e fluctuation level drops. We estimate the damping force opposing polo idal rotation experimentally and compare it with various versions of t he neoclassical theory. The experimental results agree in that the mea sured damping force has a local maxima at \M-p\ = 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.