Turbulence driven particle transport in Texas Helimak

TL;DR

This paper investigates how turbulence influences particle transport in the Texas Helimak device, revealing the role of wave-particle interactions and shear flow in modulating transport barriers.

Contribution

It provides new insights into the effects of external bias on turbulence spectra and transport mechanisms in a toroidal plasma with magnetic shear.

Findings

Negative bias induces dominant wave frequencies affecting transport.

Resonant wave-particle interactions increase transport near phase velocities.

Positive bias creates shear flow and transport barriers reducing particle flux.

Abstract

We analyze the turbulence driven particle transport in Texas Helimak (K. W. Gentle and Huang He, Plasma Sci. and Technology, 10, 284 (2008)), a toroidal plasma device with one-dimensional equilibrium with magnetic curvature and shear. Alterations on the radial electric field, through an external voltage bias, change spectral plasma characteristics inducing a dominant frequency for negative bias values and a broad band frequency spectrum for positive bias values. For negative biased plasma discharges, the transport is high where the waves propagate with phase velocities near the plasma flow velocity, an indication that the transport is strongly affected by a wave particle resonant interaction. On the other hand, for positive bias the plasma has a reversed shear flow and we observe that the transport is almost zero in the shearless radial region, an evidence of a transport barrier in this region.