Extraction physics in volume H−-ion sources

Bacal, M.; Hatayama, A.; Matsumiya, Tooru; Hamabe, M.; Kuroda, T.; Oka, Y.

doi:10.1063/1.2149367

Cited by 4 publications

(3 citation statements)

References 10 publications

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“…It is important to calculate the ratio I − /I e when the density of these particles is measured in the neighbourhood of the extraction opening. Since in the contemporary negative ion sources a transverse magnetic field is present in front of the PE, a collisional flux model for diffusion of electrons across the magnetic field has been proposed [63]. One of the analysed cases is that of data taken in NIFS [34].…”

Section: Extraction Physicsmentioning

confidence: 99%

Physics aspects of negative ion sources

2006

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The physical phenomena important in volume and surface production negative hydrogen ion sources are reviewed. The phenomenon, designated volume production, was attributed to dissociative electron attachment of low energy electrons to rovibrationally excited molecules. The experimental verification in 2005 of the reality of this mechanism is reported. Recent results obtained by measuring the negative ion temperature in a filament discharge ion source indicate that two negative ion populations are present. Understanding the physics of volume negative ion sources operating in accelerators with H − ion density in the 100 mA cm −2 range opens the prospect of creating volume caesium-free sources for fusion. The evolution of physics of surface production is also described.A measurement effected near the plasma electrode (PE) using two-laser beam photodetachment showed the presence of a directed negative ion flow. The ratio of the negative ion and electron currents extracted through the transverse magnetic filter field near the PE can be predicted from a collisional flow model. A specific for two negative species plasmas transport mechanism in the weak transverse magnetic filter field is described.

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Section: Extraction Physicsmentioning

confidence: 99%

Physics aspects of negative ion sources

2006

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“…In other studies, Manuscript measurements of the negative-ion density n H − and electron density n e were performed in the ion sources, both in the magnetic-field-free region and in the region near the PE [2], [4], [5]. The measured ratio between the negative-ion density and electron density near the extraction aperture can be used to calculate the ratio between the extracted negative-ion current and electron current, with the application of different theoretical models for electron flux [6]. The cause of the variation in the extracted electron and negative-ion currents due to the presence of a transverse magnetic field and a positive bias on the PE was suggested by Bacal et al [2]: Electrons near the PE are trapped in the weak magnetic field (a few tens of gauss) and lost along the field lines, whereas positive ions are not trapped because of their large Larmor radius.…”

Section: Introductionmentioning

confidence: 99%

Plasma Electrode Bias Effect on the $\hbox{H}^{-}$ Negative-Ion Density in an Electron Cyclotron Resonance Volume Source

Svarnas

Breton

Bacal

et al. 2007

IEEE Trans. Plasma Sci.

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The role of the plasma electrode (PE) bias in the extraction process in a large-volume hybrid multicusp negativeion source, which is driven by 2.45-GHz microwaves, is studied. Spatially resolved negative-ion and electron density measurements close to the extractor aperture were performed under various pressures (1-4 mtorr) by means of the electrostatic probe and photodetachment technique. As the low positive voltage applied to the PE is slightly increased (from 4 to 7 V), the electron temperature passes through a minimum (0.2-0.6 eV), while simultaneously, both the negative-ion density and the H − extracted current reach a maximum (∼1−2 × 10 9 cm −3 and ∼ 0.5 mA/cm 2 , respectively). Optimum pressure values for the extracted negativeion current and the negative-ion density are found between ∼1.5 and 3 mtorr. It is deduced that the negative-ion density measured in the center of the source cannot be directly correlated with the ion extracted current. The electron density and the associated extracted electron current linearly decrease as a function of the PE bias. The physical mechanisms explaining the experimental results are discussed.

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“…Negative ion sources for the neutral beam injector (NBI) of ITER must meet fundamental requirements, among which we consider here are large ion current density, low ratio R j of electron to ion current, and careful computation of the beam trajectory [3]- [5]. Since negative ions are easily destroyed (by mutual neutralization or by electron impact detachment strongly increasing with electron energy), their mean adsorption path λ a is small (few centimeters).…”

Section: Introductionmentioning

confidence: 99%

Negative Ion Extraction With Finite Element Solvers and Ray Maps

Cavenago

Veltri²,

Sattin³

et al. 2008

IEEE Trans. Plasma Sci.

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The negative ion production and extraction are critical aspects of the neutral beam injector for ITER, so that improvements in their physical understanding are expected to contribute to the optimization of the injector design. A self-consistent 2-D model of the formation and acceleration of a beam of negative ions (including the sheath) is presented here, with plasma presheath replaced by a boundary condition (on a so-called start line) consistent with the 1-D complete plasma equations. An equivalent volume production before the start line is assumed. Negative beam space charge is expressed in terms of a current modulus j Σ (z, x), coupled to the adimensional electric potential u. Solution is obtained with a partial differential equation finite element solver for u and with an iterative approach for j Σ . A continuous map of particle orbits or rays (efficiently generated by interpolation) is used to improve the traditional discrete ray tracing; moreover, beam edge resolution is refined. Results include detailed information on plasma meniscus and beam skin structure.

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Extraction physics in volume H−-ion sources

Cited by 4 publications

References 10 publications

Physics aspects of negative ion sources

Physics aspects of negative ion sources

Plasma Electrode Bias Effect on the $\hbox{H}^{-}$ Negative-Ion Density in an Electron Cyclotron Resonance Volume Source

Negative Ion Extraction With Finite Element Solvers and Ray Maps

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