Development of Cs-Free Negative-Ion Source by Sheet Plasma

Hanai, Keito; Takimoto, Toshikio; Kaminaga, Hiroki; Tonegawa, Akira; Sato, Kohnosuke; Kawamura, Kazutaka

doi:10.1585/pfr.15.2401029

Cited by 4 publications

(3 citation statements)

References 15 publications

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“…The experiment was performed using the Cs-free negativeion source TPDsheet-U apparatus, which is schematically illustrated in figure 1 [10][11][12][13][14][15]. TPDsheet-U is divided into two regions: the sheet plasma source and extraction regions.…”

Section: Cs-free Negative-ion Source Tpdsheet-umentioning

confidence: 99%

“…The volume production of negative hydrogen ions in the produced magnetized sheet plasma is proposed to be developed as a negative-ion source using test plasma produced by direct current for sheet plasma upgrade (TPDsheet-U) [10][11][12][13][14][15]. High-density magnetized sheet plasmas are suitable for producing H − ions in dissociative attachment (DA) processes because of the narrow space (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…In a previous study, high-density H − ion sheet plasmas were generated using TPDsheet-U, and H − ion current densities of over 20 mA cm −2 were obtained under the following conditions: a gas pressure of 0.3 Pa, a discharge current of 80 A, an external magnetic field of ∼40 mT, and an extraction voltage of 10 kV. However, the co-extracted electron current is ∼10 times the negative-ion current, and the thermal damage caused by this electron poses a problem in the long-operation of the negative-ion source TPDsheet-U [12,13]. An electron fence (EF) was installed on the extraction grid (PG).…”

Section: Introductionmentioning

confidence: 99%

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

Tonegawa¹,

Kaminaga²,

Hanai³

et al. 2021

Nucl. Fusion

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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.

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Section: Cs-free Negative-ion Source Tpdsheet-umentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Tonegawa¹,

Kaminaga²,

Hanai³

et al. 2021

Nucl. Fusion

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Characteristics of extracted ion beam from a cesium-free negative ion source using sheet plasma

Kaminaga

Takimoto

Tonegawa

et al. 2020

Review of Scientific Instruments

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We report the characteristics of extracted beam current in the test plasma produced by direct current for sheet plasma upgrade producing negative ions by volume production without cesium (Cs) seeding. The negative hydrogen ion beam is extracted by a two-grid extraction system, which is located at the periphery of the sheet plasma. Experimental observations show that (i) negative hydrogen ions are successfully extracted from the sheet plasma by single/multi-aperture grids and (ii) the ratio of the extracted electron current IEG(e) and the hydrogen negative ion current IEG(H−), IEG(e)/Ic(H−), decreases from 8.0 to 2.0 with an increase in the height of the electron fence (HEF), which is a filter that prevents electron diffusion from the extraction region.

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Hydrogen negative ion density measurement by laser photodetachment and the effect of H recombination on the walls

Park

Kwak

et al. 2021

Physics of Plasmas

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A laser photodetachment (LPD) was applied to measure the absolute hydrogen negative ion (H−) density in an RF negative ion source. The ion source has been developed to study a Cs-free ion source utilizing a magnetic filter by permanent magnets to enhance the volume production of H− in the extraction region. Prior to a beam extraction experiment, the laser photodetachment was applied as an initial performance evaluation. The absolute H− densities were obtained by LPD with the variation of the RF power. The H− density reached 1.8×109 cm−3 at an RF power of 5 kW. The comparison with the calculation of a particle balance model showed the discrepancy between the model and the LPD results. The LPD result showed the rapid increase in H− density with respect to the RF power compared to the model. By assuming the wall temperature increase and adjusting the recombination coefficient (γrec) of hydrogen (H) atoms on the walls, the discrepancy could be resolved. The recombination coefficient (γrec) plays an important role in determining the H− density in view of the fact that it can affect both the generation and the destruction processes of H−.

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Development of Cs-Free Negative-Ion Source by Sheet Plasma

Cited by 4 publications

References 15 publications

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

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

Characteristics of extracted ion beam from a cesium-free negative ion source using sheet plasma

Hydrogen negative ion density measurement by laser photodetachment and the effect of H recombination on the walls

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