Experimental Studies of Electric Currents in the Divertor Plasma of a Helical Device

In the I = 2lm = 19 Heliotron E device, with currentless NBI and NBI+ECH plasmas, measurements were made of electric currents flowing to grounded collector plates installed near the vacuum chamber wall in 4 poloidal cross-sections of the torus within l/2 helical pitch. A strong up-down asymmetry in both absolute value and sign was observed in the currents flowing along the diverted field lines. In general case, the value and direction of the current depended on absorbed power. Proceeding from the character of current responce to fast variations of the heating power, it was hypothesized that non-ambipolar divertor flows were strongly affected by dynamics of suprathermal particles occurring in the plasma during NBI and ECH. Keywords: heliotron, divertor, non-umbipolar flow, up-down asymmetry, helical ripple asymmetry, fast particle