LAUSR

The progress toward realizing a high-performance cesium (Cs)-free negative-ion source based on volume production in a magnetized sheet plasma device (TPDsheet-U) is reported. In the experiments, H− ions were successfully extracted from sheet plasma using single-/multi-aperture grids. The experimental results of the single-aperture grid show that the negative hydrogen ion current density (J C(H−)) performance of Cs-free H− ion beams in TPDsheet-U is about one-fourth that of Cs-containing H− ion sources in the ITER negative-ion neutral-beam injector (NNBI). (i) The J C(H−) was ∼7.5 mA cm−2 at an extraction voltage of 10 kV, a discharge current I d of 90 A, and a gas pressure of 0.3 Pa. (ii) The electron current J EG(e) with this soft magnetic filter (SMF) was only ∼10% of the electron current without the SMF; The J EG(e)/J C(H−) ratio was reduced below 0.4 at y < 18 mm for a single-aperture grid with the SMF at I d = 50 A and external magnetic field strength of 38 mT.