Relationship between extraction of H− ions optimized by plasma grid potential and plasma parameters in a bucket source

Fukumasa, Osamu; Hosoda, Masayuki; Naitou, Hiroshi

doi:10.1063/1.1142826

Cited by 26 publications

(17 citation statements)

References 8 publications

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“…It has also been shown [24][25][26] that inserting and biasing plasma electrodes (PEs) close to the negative ion extractor affect directly the extracted negative ion and electron currents. In particular, it exists an optimum bias V PE,opt , slightly larger than the bulk plasma potential.…”

Section: Introductionmentioning

confidence: 99%

Negative ion extraction from hydrogen plasma bulk

et al. 2013

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International audienceA two-dimensional particle-in-cell/Monte Carlo collision model has been developed and used to study low electronegative magnetized hydrogen plasma. A configuration characterized by four electrodes is used: the left electrode is biased at Vl = −100 V, the right electrode is grounded, while the upper and lower transversal electrodes are biased at an intermediate voltage Vud between 0 and −100 V. A constant and homogeneous magnetic field is applied parallel to the lateral (left/right) electrodes. It is shown that in the magnetized case, the bulk plasma potential is close to the transversal electrodes bias inducing then a reversed sheath in front of the right electrode. The potential drop within the reversed sheath is controlled by the transversal electrodes bias allowing extraction of negative ions with a significant reduction of co-extracted electron current. Furthermore, introducing plasma electrodes, between the transversal electrodes and the right electrode, biased with a voltage just above the plasma bulk potential, increases the negative ion extracted current and decreases significantly the co-extracted electron current. The physical mechanism on basis of this phenomenon has been discussed

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Section: Introductionmentioning

confidence: 99%

Negative ion extraction from hydrogen plasma bulk

et al. 2013

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“…However, the rf source in its present design of a large-scale two-chamber source does not ensure efficiency high enough for volume production of the ions, and currently it is considered as a source with surface production of the ions. [2][3][4] The design of the rf sources of negative hydrogen ions is based on the experience accumulated during many years of work on the dc filament sources [5][6][7][8][9][10][11][12][13][14] starting in the 1980s, the time when the idea for the tandem type of the source arouse. The idea is for a design that ensures spatial separation in the source of two regions, respectively, of high-and low electron temperature, and it originates from the conclusion that such a design provides conditions favoring the two-step reaction of the volume production of the negative ions: excitation of the molecules to highly vibrationally excited states that requires high-energetic electrons and production of negative ions via dissociative attachment of electrons to the vibrationally excited molecules that requires low-energetic electrons.…”

Section: Introductionmentioning

confidence: 99%

A small radius hydrogen discharge: An effective source of volume produced negative ions

Paunska

Shivarova

Tarnev

2010

Journal of Applied Physics

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Free-fall regime maintenance of hydrogen discharges is analyzed based on numerical solutions of a set of equations involving the balance equations of the charged particles [electrons, the three types of the positive ions (H+, H2+, and H3+), and negative H− ions] and of the neutral species (hydrogen atoms H and vibrationally excited molecules), the momentum equations of the positive ions, the electron energy balance equation, and the Poisson equation, all together 25 differential equations. The obtained results for varying discharge radius show strong accumulation of the negative ions in the on-axis region of the discharge when the discharge radius is small, which leads to a concept for a design of a volume-production based source as a matrix of small radius discharges. The variation in the negative ion density with changing gas pressure and electron density at the discharge axis is also analyzed.

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“…Its effect for cooling the electrons has been proved both experimentally [3,6,7,13,[20][21][22][23][24][25][26], by probe diagnostics and measurements of the current density of the extracted negative ions, and theoretically [6][7][8][9][10][11][12]15,27] by modelling and discussions on the mechanisms governing the operation of the filter. The fluid-plasma models [6][7][8][9][10]15] of the magnetic filter involve importance of the transport processes.…”

Section: Introductionmentioning

confidence: 99%

Magnetic filter operation in hydrogen plasmas

Kolev

Lishev

Shivarova

et al. 2007

Plasma Phys. Control. Fusion

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Abstract. Fluid-plasma model description of the operation of a magnetic filter for electron cooling in gas-discharge plasmas is presented in the study. Directed to the use of weak magnetic fields in the sources of negative hydrogen ion beams for additional heating of fusion plasmas, hydrogen discharges have been considered. The numerical results obtained within a 2D model are stressed. The 1D model presented aims at showing main trends whereas the results obtained within the 3D model, also developed, come to confirm the 2D-model description. The models outline importance of the transport phenomena: electron-energy and charged-particle fluxes. Reduction of the thermal flux across the magnetic field together with thermal diffusion and diffusion, acting in a combination, are in the basis of the electron cooling and of the spatial distribution of the electron density. Effects due to the ) ( B E × -drift and to the diamagnetic drift form the fine spatial structure of the plasma-parameter variations. IntroductionThe development of sources of negative ion beams for fusion plasma heating by neutral beam injection [1-4] is one of the stimuli motivating the active research on low-pressure hydrogen discharges. In general, the sources of negative hydrogen ions with volume-production based processes as well as the hybrid sources where surface production is employed are tandem-type sources with a construction ensuring space separation of regions of high and low electron temperature [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Thus, electron cooling in the discharge is needed and this is provided by a magnetic filter.The magnetic filter is a localized transverse magnetic field. Its effect for cooling the electrons has been proved both experimentally [3,6,7,13,[20][21][22][23][24][25][26], by probe diagnostics and measurements of the current density of the extracted negative ions, and theoretically [6][7][8][9][10][11][12]15,27] by modelling and discussions on the mechanisms governing the operation of the filter. The fluid-plasma models [6][7][8][9][10]15] of the magnetic filter involve importance of the transport processes. However, the different models stress different aspects as mechanisms of the filter operation: (i) reduction of the electron mobility and of the diffusion in magnetized plasmas acting in a combination with the temperature dependence of the Coulomb collision frequency, the latter considered as a factor ensuring lower diffusion of the hot electrons; (ii) thermal conductivity effects, again acting together with Coulomb collisions; (iii) importance of the Lorentz force showing evidence due to cancelled effects of the -) ( B E × and diamagnetic drifts; (iv) importance of the diamagnetic drift; (v) diffusion acting together with elastic electron-neutral collisions. Both 1D and 2D models have been developed, however, as it has been usually stressed, 2D models are needed for proper description of the problem. Due to the complexity of the description, simplifying assumptions, like neglecting of col...

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Relationship between extraction of H− ions optimized by plasma grid potential and plasma parameters in a bucket source

Cited by 26 publications

References 8 publications

Negative ion extraction from hydrogen plasma bulk

Negative ion extraction from hydrogen plasma bulk

A small radius hydrogen discharge: An effective source of volume produced negative ions

Magnetic filter operation in hydrogen plasmas

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