Research progress on ionic plasmas generated in an intense hydrogen negative ion source

Takeiri, Y.; Tsumori, K.; Ikeda, K.; Nakano, H.; Kisaki, M.; Nagaoka, K.; Tokuzawa, T.; Geng, Suiyan; Osakabe, M.; Kaneko, O.; Kondo, Tomoki; Sato, Mamoru; Shibuya, Masayuki; Komada, S.; Sekiguchi, Hiroyuki

doi:10.1063/1.4916473

Cited by 8 publications

(3 citation statements)

References 8 publications

(10 reference statements)

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“…Simonin et al [4] and Fantz et al [2] describe the research and development efforts dedicated in Europe to the NBI for the tokamak DEMO. In Japan the superconductor helical system, Large Helical Device (LHD) at National Institute for Fusion Science, is now investigating deuterium plasmas with negative ion based neutral beam heating charged with deuterium [25]. A negative ion source cannot produce negative deuterium (D − ) ion current as large as the negative hydrogen (H − ) ion current using identical parameters, e.g.…”

Section: Introductionmentioning

confidence: 99%

Negative ion source operation with deuterium

Bacal

Wada

2020

Plasma Sources Sci. Technol.

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When the working gas of a negative ion source is changed from hydrogen to its isotope, deuterium, an ‘isotope effect’ is observed; namely, several plasma characteristics such as the electron energy distribution, the atomic fraction and the spectra of rovibrationally excited molecules change. The understanding of the effect becomes more important, as research and development aiming at ITER power level operation is being challenged with feeding deuterium to the ion sources. As a historical review of the effort to develop hydrogen/deuterium negative ion sources, several types of negative ion sources designed for the neutral beam plasma heating are described: double charge exchange sources, volume sources and surface-plasma sources. The early results with volume sources operated with and without cesium are introduced. The characteristics of the source charged with deuterium are compared to those of the source charged with hydrogen. The isotope effect did not appear pronounced as the negative ion density was measured in a small source but became more pronounced when the plasma source size was enlarged and the discharge power density was increased to higher values. Surface plasma sources were optimized for deuterium operation but could not achieve the same performance as a source operated with hydrogen at the same power and pressure. The lower velocity of negative deuterium ions leaving the low work function surface seemed to limit the production efficiency. Fundamental processes causing these differences in negative ion source operation are summarized. After explaining the current status of negative ion source research and development, the acquired knowledge is utilized to the development of large negative ion sources for nuclear fusion research and to the development of compact negative ion sources for neutron source applications.

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Section: Introductionmentioning

confidence: 99%

Negative ion source operation with deuterium

Bacal

Wada

2020

Plasma Sources Sci. Technol.

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“…The negative saturation current is lower on the aperture than that on the peripheral region and the current has an increment during beam ex- traction. Since the result using cavity ring-down measurement has shown that the negative ion density is uniform in Y direction [9], and the probe are sensitive to the electrons, the variation in the distribution of negative saturation current is caused by electrons. Magnetic cusps due to electron deflection magnet exist between two apertures as shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Spatial Distributions of Charged Particles and Plasma Potential before and during Beam Extraction in a Negative Hydrogen Ion Source for NBI

Geng

Tsumori

Nakano

et al. 2015

Plasma and Fusion Research

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In order to understand the physics of the production and extraction mechanism of negative ions, experiments with a single Langmuir probe are carried out to investigate the local spatial distribution of the plasma in the vicinity of the plasma grid in a negative hydrogen ion source. The results show that the electron density is lower in the aperture region than that in its peripheral region. It is attributed to the cusp magnetic field introduced with the electron deflection magnets near the plasma grid. In addition, the linkage of the filter field with the electron deflection magnetic field contributes to the increment of electron density. The profile of plasma potential indicates that an electric field exists between the aperture and its peripheral region, and then a local negative ion flow can be introduced near the plasma grid.

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“…They are aimed to compensate the zigzag deflection of H − beamlets [24,25]. Here, the application of ADCM to the CRAFT quarter-size negative ion source is more expected to suppress the number of co-extracted electrons with the higher magnetic field in front of the PG [26][27][28]. Furthermore, the current flow through the PG (typical value 1-1.3 kA) is used to produce the magnetic filter field (MFF) [29].…”

Section: Methodsmentioning

confidence: 99%

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

Yang,

Wei,

et al. 2024

Plasma Phys. Control. Fusion

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The negative ion based neutral beam injection (NNBI) is a desirable plasma heating and current drive method for the large-scale magnetic fusion devices. Due to the strict requirements and difficult development of the negative ion source for fusion, a long-pulse negative ion source has been developed under the framework of the Comprehensive Research Facility for Fusion Technology (CRAFT) in China. This negative ion source consists of a single RF driver plasma source and a three-electrode accelerator. The typical extraction and acceleration voltage are 4~8 kV and 40~50 kV, respectively.During one shot of the long-pulse (~100 s) beam extraction, the gas pressure in the vacuum vessel increased sharply and the temperature of the cryopump rise from 8 K to 20 K. Moreover, the vessel wall appeared a high temperature after several long-pulse shots. A self-consistent simulation of beam-gas interaction revealed that the heat loads on the vessel wall should be caused by the stray electrons ejecting from the accelerator. Those stray electrons are mainly generated via the stripping or ionization collisions and strongly deflected by the downstream side of the deflection magnetic field for the co-extracted electron. The location of hot spots measured by infrared thermography is consistent with the simulation results. To solve this problem, a series of electron dumps are designed to avoid the direct impinging of the ejecting electrons on the cryopump and the vessel wall. And the results suggest that the hot spots are almost eliminated.

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Research progress on ionic plasmas generated in an intense hydrogen negative ion source

Cited by 8 publications

References 8 publications

Negative ion source operation with deuterium

Negative ion source operation with deuterium

Spatial Distributions of Charged Particles and Plasma Potential before and during Beam Extraction in a Negative Hydrogen Ion Source for NBI

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

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