Abstract
The magnitude of the radial electric field (Er), resulting from nonambipolar fluxes of neoclassical origin, is evaluated using Monte Carlo guiding-center simulations for a low-current plasma corresponding to the FT-2 tokamak {Fisichiskii Tokamak-2, Ioffe Institute, St. Petersburg [S. I. Lashkul, V. N. Budnikov, E. O. Vekshina et al., Plasma Phys. Rep. 27, 1001 (2001)]}. The Er-values are found to significantly exceed those given by the standard neoclassical theory, based on thin-orbit assumption, when the plasma current is sufficiently low and the pressure gradient is sufficiently high. Strong Er-structures are found to form in the same low plasma-current range where enhanced confinement is reported in the FT-2 tokamak. In the simulations, the physics behind the strong increase in the field values is intimately related to the poloidal Mach-number, together with the wide ion orbits.
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