Calculation of the radial electric field from a modified Ohm's law

Abstract

A modified Ohm's Law, derived from the conservation of deuterium and carbon ions and electron momentum and the requirement for charge neutrality, yields an expression for the radial electric field, Er, in the edge pedestal region in terms of the motional electric field due to the carbon and deuterium ion rotation velocities as well as pressure gradients and the radial plasma current. This analytical Ohm's Law model for Er is first shown to be consistent with the conventional “experimental” electric field calculated from the carbon radial momentum balance using experimental carbon rotation and pressure gradient measurements when experimental profiles are used to evaluate the Ohm's Law in three DIII-D [Luxon, Nucl. Fusion 42, 614 (2002)] representative discharges (for L-mode, H-mode, and Resonant Magnetic Perturbation operating regimes). In order to test the practical predictive ability of the modified Ohm's Law, the calculations were repeated using rotation velocities calculated with neoclassical rotation models instead of measured rotation velocities. The Ohm's Law predicted Er using theoretical rotation velocities did not agree with the “experimental” Er as well as the Ohm's Law prediction using experimental rotation velocities, indicating that more accurate models for predicting edge rotation velocity are needed in order to have a validated predictive model of Er in the plasma edge.