Effect of grid bias upon negative ion density in a magnetized plasma

Abstract

A hydrogen plasma magnetized by a pair of Helmholtz coils was separated into two regions by inserting a metallic grid. The region with discharge filaments was separated from a low-density-plasma region without filaments by the grid. The effect of the mesh grid potential and that due to the linear magnetic field upon the hydrogen negative ion (H⁻) density in the low-density-plasma region were investigated with the direct current laser photodetachment method. The electron temperature at the center of the low-density-plasma decreased from 1.5 to 0.5 eV while the electron density increased from 2×10¹⁰ to 6×10¹⁰ cm⁻³ by reducing the grid bias from +20 to −60V. The ratio of the H⁻ density to the electron density increased from 9 to 13 % by applying the linear magnetic field to the hydrogen plasma.