Study of Gasdynamic Electron Cyclotron Resonance Plasma Vacuum Ultraviolet Emission to Optimize Negative Hydrogen Ion Production Efficiency

TL;DR

This study investigates vacuum ultraviolet emission in gasdynamic electron cyclotron resonance plasmas to optimize negative hydrogen ion production, revealing emission patterns and proposing modifications for enhanced efficiency.

Contribution

It provides experimental insights into VUV emissions in high-density ECR plasmas and suggests modifications to improve negative hydrogen ion production efficiency.

Findings

VUV power varies across emission ranges with source parameters.

Molecular continuum dominates in the first chamber, Lyα in the second.

Proposed modifications aim to optimize negative ion yield.

Abstract

Negative hydrogen ion sources are used as injectors into accelerators and drive the neutral beam heating in ITER. Certain processes in low-temperature hydrogen plasmas are accompanied by the emission of vacuum ultraviolet (VUV) emission. Studying the VUV radiation therefore provides volumetric rates of plasma-chemical processes and plasma parameters. In the past we have used gasdynamic ECR discharge for volumetric negative ion production and investigated the dependencies between the extracted H$^-$ current density and various ion source parameters. It was shown that it is possible to reach up to 80 mA/cm$^2$ of negative ion current density with a two electrode extraction. We report experimental studies on negative hydrogen ion production in a high-density gasdynamic ECR discharge plasma consisting of two simple mirror traps together with the results of VUV emission measurements. The VUV-power was measured in three ranges -- Ly$_\alpha$, Lyman band and molecular continuum -- varying the source control parameters near their optima for H$^-$ production. It was shown that the molecular continuum emission VUV power is the highest in the first chamber while Ly$_\alpha$ emission prevails in the second one. Modifications for the experimental scheme for further optimization of negative hydrogen ion production are suggested.