Response of H− ions to extraction field in a negative hydrogen ion source

Geng, Suiyan; Tsumori, K.; Nakano, H.; Kisaki, M.; Ikeda, K.; Osakabe, M.; Nagaoka, K.; Takeiri, Y.; Shibuya, Masayuki

doi:10.1016/j.fusengdes.2017.02.041

Cited by 12 publications

(5 citation statements)

References 15 publications

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“…Last, note that in accordance with experiments (see Fig. 5 of Geng et al 146 ), we observe in Fig. 12 a shift of the x-point from the axis of the aperture which, is due to slight magnetisation of the negative ions by the magnetic filter field.…”

Section: Extraction Of Negative Ionssupporting

confidence: 91%

Tutorial: Modeling of the extraction and acceleration of negative ions from plasma sources using particle-based methods

Garrigues

Fubiani

2023

Journal of Applied Physics

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In this Tutorial, we consider plasma sources with applications to fusion devices and high energy accelerators. These ion sources typically produce negative ions from hydrogen-isotope gases, which are extracted through one or multiple apertures and accelerated to high kinetic energies. Next, they are either double stripped of two electrons to form positive ions used as precursors in accelerator devices or neutralized to produce a neutral beam injected in tokamak reactors. Contrary to the working conditions of most ion sources where volume production prevails, the mechanism of negative ion production by dissociative electron attachment on vibrationally excited molecules inside the plasma volume of fusion-type hydrogen-fueled high power discharges is mostly balanced by their destruction by detachment before being extracted rendering this means of producing negative ions rather inefficient. Surface production through the transfer of electrons from low work function metallic materials to the impacting atoms is the alternative solution to fulfill the requirements for the applications concerned. Negative ions are produced close to the aperture from which they are extracted. As a result, the analysis and understanding of the extraction mechanisms through experimental diagnostics is rather difficult due to the lack of accessibility and can only give a partial view. In addition, most of the experimental work is focused on the validation of requirements for the applications and not to the investigation of the fundamental processes that take place inside these types of sources. This Tutorial is focused on the description and understanding of the physical mechanisms behind the extraction and acceleration of negative ions from hydrogen plasma sources through modeling methods. We describe the numerical techniques of particle-based methods with a specific emphasis on particle-in-cell Monte Carlo collision algorithms. An analysis of the physical processes involved in driving the negative ions from the plasma source, across the apertures and inside the accelerator as reported in the literature, is presented in detail. This Tutorial concludes with additional and future works to be addressed in the coming years.

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Section: Extraction Of Negative Ionssupporting

confidence: 91%

Tutorial: Modeling of the extraction and acceleration of negative ions from plasma sources using particle-based methods

Garrigues

Fubiani

2023

Journal of Applied Physics

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“…The negative ion current density profile is asymmetric due to the slight magnetization of the ions. The x-point visible on the current streamlines is shifted off axis which is consistent with experimental measurements [146]. The ratio of the extracted ion current originating from the chamfered surface compared to the flat side facing the plasma (see Fig.…”

Section: Negative Ion Extractionsupporting

confidence: 88%

Latest experimental and theoretical advances in the production of negative ions in caesium-free plasmas

et al. 2021

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This topical review gathers the last updates concerning caesium-free negative ion sources presented during the 63rd Course of the International school of Quantum Electronics of the Ettore Majorana Foundation and European collaborative works related to these lectures. Hence, beyond the frame of this course this topical review addresses both theoretical and experimental work performed during these last few years and complexities represented by the conception of a negative ion source ranging from the creation of negative ions to their neutralization.

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“…Here, we will discuss a distribution of negative-ion density and electron density perpendicular to the PG surface to understand electron contamination in the beam. We obtained the flow direction of negative hydrogen ions during beam extraction by laser-assisted directional LP in RNIS [25,29]. According to the result, the turning point of negative hydrogen ions released from the PG surface returning to the PG direction was approximately 20 mm from the PG.…”

Section: Increase Of Deuterium Negative Ion Current Achieved By Suppr...mentioning

confidence: 99%

“…The extraction distribution of hydrogen negative ions was strongly distributed near the PG aperture in the range of 0 < z < 20 mm, here z is the distance from the PG surface, which is closely related to the distribution of the EDM field in the vicinity of the PG surface. A negative-ionrich plasma with low electron is formed in the region between PG and EDM lobe [22,29]. The negative-ion density should decrease outside the turning point of negative ions, and it is assumed that the inflow of electrons from the discharge region increases.…”

Section: Increase Of Deuterium Negative Ion Current Achieved By Suppr...mentioning

confidence: 99%

Exploring deuterium beam operation and the behavior of the co-extracted electron current in a negative-ion-based neutral beam injector

et al. 2019

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Achievements of the deuterium beam operation of the negative-ion-based neutral beam injector (N-NBI) in the Large Helical Device (LHD) are reported. In the beam operation in LHD-NBIs, both hydrogen (H) and deuterium (D) neutral beams were generated by changing the operation gas using the same accelerator. The maximum accelerated deuterium negative ion current (I acc(D) ) reaches 46.2 A from two beam sources with the averaged current density being 190 A/m 2 for 2 sec, and the extracted electron to accelerated ion current ratio (I e /I acc(D) ) increases to 0.39 using 5.6 V high bias voltage in the first deuterium operation in 2017. Increase of electron density in the vicinity of the plasma grid surface, which is considered the main reason of increasing co-extracted electrons in a beam, is confirmed by half-sized research negative ion source in the neutral beam test stand in NIFS. The deuterium negative ion density is also larger than the hydrogen negative ion density in the vicinity of plasma grid surface using the same discharge condition. In the latest experimental campaign in 2018, the I acc(D) increases to 55.4 A with the averaged current density being 233 A/m 2 for 1.5 sec using the shot extraction gap length. The low I e /I acc(D) of 0.31 can be maintained by high discharge power. The various parameters mentioned above are defined in detail below.

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Response of H− ions to extraction field in a negative hydrogen ion source

Cited by 12 publications

References 15 publications

Tutorial: Modeling of the extraction and acceleration of negative ions from plasma sources using particle-based methods

Tutorial: Modeling of the extraction and acceleration of negative ions from plasma sources using particle-based methods

Latest experimental and theoretical advances in the production of negative ions in caesium-free plasmas

Exploring deuterium beam operation and the behavior of the co-extracted electron current in a negative-ion-based neutral beam injector

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