Recovery of cesium in the hydrogen negative ion sources

Abstract

Cesium recovery from the polluted layers in the 1/3 scale hydrogen negative ion source for LHD-NBI system has tested. It was found that the cesium recovery can be produced by additional discharges as from the cesium layer, aged by tungsten and residual gas, so as from the cesium layers, polluted by an occasional water leak. The highest cesium recovery to negative ion production was produced by a xenon arc, while glow discharge and arcing in hydrogen were less effective. The mechanism of recovery is the ejection of cesium from the underlying enriched layer by the arc and its transport to the surface.

Optimization of Cs deposition in the 1/3 scale hydrogen negative ion source for the large helical device-neutral beam injection system

“…The study of NI production with direct deposition of cesium onto MS internal walls was done recently at the National Institute for Fusion Science. These experimental data and the experiments on cesium recovery from polluted layers in the internal walls 9 confirm the surface origin of NI yield improvement in the MS 10 and show that a dynamic cesium-tungsten coverage of the PG surface supports the enhanced H Ϫ production. The results of a NI production study with direct deposition of well-defined cesium amounts are described below.…”

“…The described data on H Ϫ production with the directed deposition of cesium into the MS and the data on cesium recovery from the polluted layers in the MS 9 shows that a dynamic cesium-tungsten coverage of the PG surface supports the enhanced H Ϫ production. 10 The surface NI production is maximal at the optimal cesium coverage and it needs only a small amount of cesium on molybdenum ͑or tungsten͒ of about ϳ0.7Х2 -3 ϫ10 14 cm Ϫ2 Х0.5-0.8 mg/m 2 .…”