Observation of oscillatory radial electric field relaxation in a helical plasma

TL;DR

This paper reports the first direct observation of oscillatory relaxation of zonal electrostatic potential perturbations in a non-axisymmetric stellarator, providing insights into turbulence damping mechanisms in magnetic confinement plasmas.

Contribution

It presents experimental evidence of oscillatory zonal potential relaxation in a stellarator, aligning with theoretical models and advancing understanding of turbulence damping.

Findings

Observation of damped oscillations in electrostatic potential after pellet injection

Waveform matches theoretical predictions for non-axisymmetric geometries

First direct measurement of collisionless damping of zonal flows in such systems

Abstract

Measurements of the relaxation of a zonal electrostatic potential perturbation in a non-axisymmetric magnetically confined plasma are presented. A sudden perturbation of the plasma equilibrium is induced by the injection of a cryogenic hydrogen pellet in the TJ-II stellarator, which is observed to be followed by a damped oscillation in the electrostatic potential. The waveform of the relaxation is consistent with theoretical calculations of zonal potential relaxation in a non-axisymmetric magnetic geometry. The turbulent transport properties of a magnetic confinement configuration are expected to depend on the features of the collisionless damping of zonal flows, of which the present letter is the first direct observation.