Characteristics of plasma grid bias in large-scaled negative ion source

Abstract

The electron density was measured at various bias voltages to understand how the plasma grid bias affects the electron near the plasma grid in large-scaled negative ion sources. It was found that the response of the electron to the bias voltage changes depending on negative ion production processes. The electron density remarkably decreases with increasing the bias voltage in the pure-volume plasma. On the other hand, the electron density depends on the bias voltage weakly in the Cs-seeded plasma. In addition, it was observed that the response of the co-extracted electron current to the bias voltage has similar trend to that of the electron density.

Evaluation of negative ion distribution changes by image processing diagnostic

“…We have observed monotonically decreased H α intensities toward to the PG surface in both cases, and this intensity decrease with increasing bias voltage. This result is similar to the distribution of electron density measured by a surface wave probe in the pure volume plasma [12]. According to this result, electron density distribution follows positive ion distribution, which is formed by the transverse ions across the magnetic filter field due to its large Larmor radius, by charge neutrality.…”

Demonstration of Beam Optics Optimization Using Plasma Grid Bias in a Negative Ion Source

“…In negative ion sources for fusion, the PG is positively biased with respect to a discharge chamber in order to suppress electrons extracted with negative ions [1]. In recent studies, reduction of negative ion and electron densities in the vicinity of the PG was observed as the bias voltage was increased [2,3]. In addition, the numerical simulation pointed out that the curvature of the meniscus depends on the H + or H − profile near the PG [4].…”

Diagnostics tools and methods for negative ion source plasmas, a review

“…On the other hand, the spectrum emitted from a Cs atom (Cs I) is clearly observed in optical emission spectroscopy. Although the influence of Cs is expected to be small as mentioned by Wünderlich et al, effect onto the plasma condition in the very vicinity of plasma grid with adsorbed Cs requires further investigation [85].…”