Response of a tokamak plasma to particle and momentum sources

Abstract

The response of an axisymmetric toroidal tokamak plasma to first-order particle and momentum sources is investigated. The momentum sources drive coupled poloidal and toroidal mass flows and electrostatic field evolution which relax to asymptotic values on a time scale characteristic of the dominant viscous or external drag mechanism. The asymptotic steady-state momentum balance provides the necessary condition to completely determine the ambipolar potential, the particle fluxes, and currents in the flux surfaces and, hence, to determine transport fluxes across flux surfaces. Transport fluxes are driven across flux surfaces both by interspecies collisional momentum exchange, the usual case, and by momentum exchange between the plasma and external sources and/or drags. A generalized Ohm’s law is obtained and used to determine how particle and momentum sources drive parallel currents and alter the evolution of the q profile. The theory is formulated for arbitrary plasma cross sections, beta, and collision regimes.