The level of non-thermal velocity fluctuations deduced from Doppler spectroscopy and its role on TJ-II confinement

TL;DR

This study measures non-thermal velocity fluctuations in TJ-II stellarator plasmas using Doppler spectroscopy to understand their impact on plasma confinement.

Contribution

It introduces a method to deduce turbulence levels from Doppler temperature differences of different ion species in stellarator plasmas.

Findings

Velocity fluctuations vary with plasma density and power.

Turbulence levels correlate with confinement properties.

Method offers a new way to assess plasma turbulence.

Abstract

The goal of this investigation is to study, in the line of previous works, the level of velocity fluctuations in different scenarios of the TJ-II stellarator. The method followed consists in measuring the apparent Doppler temperature of C4+ and protons with high spectral resolution techniques with spatial resolution. The level of turbulent velocities in the plasma has been deduced from the difference observed between the apparent temperature of both species, following a method previously presented and borrowed from astrophysics. The study of this difference, as a function of plasma density and injected power, provides a way to explore if this turbulence plays any role in the confinement of the hot TJ-II plasma.