Evaluation of ambipolar potential barrier in the gas dynamic trap by Doppler spectroscopy

TL;DR

This paper uses Doppler spectroscopy to measure the ambipolar potential barrier in a gas dynamic trap, providing experimental data that supports theories on electron thermal conductivity suppression.

Contribution

It introduces a diagnostic technique based on gas jet charge exchange to measure potential profiles in the GDT plasma.

Findings

On-axis potential drop is 2.6 to 3.1 times the electron temperature.

Potential profile measurements support existing theories.

Diagnostic method enables detailed potential measurements along the line of sight.

Abstract

The recently developed Doppler spectroscopy diagnostic has been used to evaluate the height of the ambipolar potential barrier forming in the gas dynamic trap (GDT) plasma between the central cell and the region with a large magnetic expansion ratio beyond the mirror. The diagnostic technique based on the gas jet charge exchange target, allowed to measure the potential profile along the line of sight covering the radial range from the axis to the limiter. The on-axis potential drop was found to be $2.6 \div 3.1$ in units of the central plane electron temperature, which supports the existing theoretical understanding of suppression of electron thermal conductivity in the GDT expander.