Electric field profile of a Compact Helical System Heliotron/Torsatron plasma with tangential neutral beam injection

The radial electric field profiles derived from poloidal rotation velocity are compared with neoclassical estimates for a plateau regime plasma heated by a tangentially injected neutral beam in the Compact Helical System Heliotron/Torsatron device [Plasma Physics and Controlled Nuclear Fusion Research 1988 (IAEA, Vienna, 1989), Vol. 2, p. 411]. The measured electric field (Er) is more negative than the neoclassical prediction, especially near the plasma periphery. A gradient of radial electric field (∂Er/∂r) in this region is found to be more negative in the plasma with higher electron density. Although the corresponding poloidal rotation velocity is too small to trigger the L/H transition, these negative Er and ∂Er/∂r are associated with a reduction of thermal electron conductivity.