Reevaluation of the Braginskii viscous force for toroidal plasma

TL;DR

This paper reevaluates the Braginskii viscous force model in toroidal plasma, addressing previous inconsistencies and comparing theoretical predictions with experimental measurements in tokamaks.

Contribution

It provides a corrected analysis of the viscous stress tensor in toroidal plasma, including the effects of pitch angle and radial derivatives, and compares theory with experimental data.

Findings

Radial shear viscous force can develop with vertical asymmetry in ion velocity.

Qualitative agreement between theory and measurements for impure plasma discharges.

Revised model improves understanding of viscous effects in toroidal plasma confinement.

Abstract

The model by Braginskii for the viscous stress tensor is used to determine the shear and gyroviscous forces acting within a toroidally confined plasma. Comparison is made to a previous evaluation which contains an inconsistent treatment of the radial derivative and neglects the effect of the pitch angle. Parallel viscosity contributes a radial shear viscous force which may develop for sufficient vertical asymmetry to the ion velocity profile. An evaluation is performed of this radial viscous force for a tokamak near equilibrium which indicates qualitative agreement between theory and measurement for impure plasma discharges with strong toroidal flow.