<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>Formation in a Barium-Seeded Hydrogen Discharge

Leung, K. N.; Walther, S.R.; Kunkel, W.B.

doi:10.1103/physrevlett.62.764

Cited by 32 publications

(10 citation statements)

References 27 publications

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“…Both the thermal speed and flow speed of H − ions are low in our measurement, and the small velocity in the direction perpendicular to the beam extraction axis leads to the observed low beam divergence of about 5 mrad [94,95], the 95% beam emittance of 43.2±6.4 mm mrad (corresponding to the normalized 95% emittance of 0.59 mm mrad) [96], which can be deduced solely from the contribution due to a space charge effect. [98]. The present study on the H − ion transport verified that there is a net flux of H − ions from the plasma grid; the diagnostics system identified that H − ions are actually formed at the surface of low work function plasma grid.…”

Section: Negative Ion Temperaturesupporting

confidence: 69%

Diagnostics tools and methods for negative ion source plasmas, a review

Tsumori

Wada

2017

New J. Phys.

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Section: Negative Ion Temperaturesupporting

confidence: 69%

Diagnostics tools and methods for negative ion source plasmas, a review

Tsumori

Wada

2017

New J. Phys.

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“…Furthermore, barium does not present major conditioning issues and its surface can be prepared simply by argon sputtering [63]. In 1989, Leung [64] demonstrated that the injection of caesium vapour in volume sources largely increased the extracted negative-ion current. This new type of source was called a hybrid-source.…”

Section: Caesium and Its Alternativesmentioning

confidence: 99%

Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H₂/D₂ plasmas

et al. 2017

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This paper deals with a study of H − /D − negative ion surface production on diamond in low pressure H 2 /D 2 plasmas. A sample placed in the plasma is negatively biased with respect to plasma potential. Upon positive ion impacts on the sample, some negative ions are formed and detected according to their mass and energy by a mass spectrometer placed in front of the sample. The experimental methods developed to study negative ion surface production and obtain negative ion energy and angle distribution functions are first presented. Different diamond materials ranging from nanocrystalline to single crystal layers, either doped with boron or intrinsic, are then investigated and compared with graphite. The negative ion yields obtained are presented as a function of different experimental parameters such as the exposure time, the sample bias which determines the positive ion impact energy and the sample surface temperature. It is concluded from these experiments that the electronic properties of diamond materials, among them the negative electron affinity, seem to be favourable for negative-ion surface production. However, the negative ion yield decreases with the plasma induced defect density. fusion power-plant prototype producing electrical energy, targeting ∼1 GW of electrical power coupled to the grid [23,24]. In the ITER and DEMO devices, the heating of the plasma will mainly be produced by neutral beam injection (NBI). NBIs systems are key components in achieving high fusion energetic-performances. The ITER NBIs are required to inject 1 MeV beams of neutral deuterium atoms (D) into the tokamak, providing plasma heating and current drive. At such high velocities, much larger than classical electron orbit velocities of hydrogen atoms, the probability of electron capture from D + ions is too low, so that production of D relies on electron detachment from high-intensity D − beams. D − negative-ions are produced in a low-pressure plasma source and subsequently extracted and accelerated.The ITER negative ion source, currently under development at IPP Garching [7,25] in Germany, operates with a high-density, low-pressure inductively coupled plasma. Extracted D − current density of 200 A m −2 , over a large surface of 1.2 m 2 , with 5%-10% uniformity and low co-extracted electron-current (below one electron per negative ion), during long operation period (3600 s) is targeted. To reach such a high D − negative-ion current, the only up-to-date scientific solution is the use of caesium. Deuterium negative-ions are created at the extraction region by backscattering of positive ions or neutrals on the plasma grid. Deposition of caesium on the grid lowers the material work function and allows for high electron-capture efficiency by incident particles and thus, high negative ion yields. Studies conducted at IPP Garching show that the ITER negative-ion source can reach the required high current densities. However, drawbacks to the use of caesium have been identified. First, the caesium is continuously injected in the source a...

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“…The latter characteristic was proved to surpass the former as the plasma potential of a small multicusp H À source was measured by operating the source seeded with Ba. 240 When the plasma potential was made negative with respect to the chamber walls by injecting low energy electrons, the H À ion current signal decreased by a factor of 2.4, while the electron density increased by a factor of 2. The reason for the observed reduction of H À ion current despite higher electron density was considered due to the forbidden transport of surface produced H À ions originating at the chamber wall surface to the plasma volume.…”

Section: A Experimental Observationsmentioning

confidence: 99%

Negative hydrogen ion production mechanisms

Bacal

Wada

2015

Applied Physics Reviews

241

173

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International audienceNegative hydrogen/deuterium ions can be formed by processes occurring in the plasma volume and on surfaces facing the plasma. The principal mechanisms leading to the formation of these negative ions are dissociative electron attachment to ro-vibrationally excited hydrogen/deuterium molecules when the reaction takes place in the plasma volume, and the direct electron transfer from the low work function metal surface to the hydrogen/deuterium atoms when formation occurs on the surface. The existing theoretical models and reported experimental results on these two mechanisms are summarized. Performance of the negative hydrogen/deuterium ion sources that emerged from studies of these mechanisms is reviewed. Contemporary negative ion sources do not have negative ion production electrodes of original surface type sources but are operated with caesium with their structures nearly identical to volume production type sources. Reasons for enhanced negative ion current due to caesium addition to these sources are discussed. (31 pages, 265 refs

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H−Formation in a Barium-Seeded Hydrogen Discharge

Cited by 32 publications

References 27 publications

Diagnostics tools and methods for negative ion source plasmas, a review

Diagnostics tools and methods for negative ion source plasmas, a review

Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H₂/D₂ plasmas

Negative hydrogen ion production mechanisms

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H−Formation in a Barium-Seeded Hydrogen Discharge

Cited by 32 publications

References 27 publications

Diagnostics tools and methods for negative ion source plasmas, a review

Diagnostics tools and methods for negative ion source plasmas, a review

Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H2/D2 plasmas

Negative hydrogen ion production mechanisms

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Product

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Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H₂/D₂ plasmas