Characteristics of the extracted negative-ion beam in a cesium-free negative-ion source using TPDsheet-U

Abstract

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.

Langmuir-probe measurement through the plasma grid aperture of hydrogen negative ion source

“…Therefore, measuring the plasma parameters inside the EA shows preliminary results, which are important to guide our study on meniscus formation. An Example of the measurement in extraction can be found in the work of A. Tonekawa [8]. We would like to extend the study with the application of extraction field and map scan.…”