Electric Fields in a Tokamak

TL;DR

This paper investigates the apparent radial electric fields observed in tokamak experiments, proposing explanations based on impurity forces and magnetic flux shifts to clarify experimental measurements.

Contribution

It introduces two scenarios explaining the measured electric fields in tokamaks, addressing discrepancies between direct and indirect measurement methods.

Findings

Indirect measurements may reflect impurity viscous forces.

Direct measurements via motional Stark effect could detect flux-shifted electric fields.

Provides theoretical insights into electric field measurements in tokamaks.

Abstract

With the establishment of vanishing net electrostatic fields in a toroidally symmetric tokamak at equilibrium [R. W. Johnson, to appear in Phys. Rev. D], one is left needing an explanation for the measurement of an apparent radial electric field in experiments. Two scenarios are proposed, depending on the type of measurement being considered. Indirect measurement via the radial equation of motion for an impurity species possibly measures that species' net radial viscous force, and direct measurement via the motional Stark effect might reveal electric fields generated by the shifting of the toroidal magnetic flux density.