Poloidally asymmetric electrostatic potentials in closed line bumpy toroids

Abstract

Here an analytic expression is developed for the poloidal asymmetry in the electrostatic potential observed experimentally in the T mode of operation in the Elmo Bumpy Torus (EBT) [Phys. Fluids 28, 2848 (1985)]. A multiple fluid treatment for the ‘‘cool,’’ ‘‘warm,’’ and ‘‘hot’’ electrons is used. The central idea is that the ‘‘warm’’ electrons dominate both the radial and poloidal structure of the electrostatic potential in the T mode of operation. The expression for the poloidal asymmetry in the electrostatic potential, which agrees reasonably well with experiment, is also applied to a modification of the EBT magnetic configuration. It is found that a substantial reduction in the asymmetry of the electrostatic potential below that of the Elmo Bumpy Torus is possible in the modification of the EBT magnetic configuration.