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Borisov, Andrei G.; Sidis, V.; Roncin, P.; Khemliche, H.; Mertens, A.; Winter, H.

doi:10.1103/physrevb.67.115403

Cited by 13 publications

(10 citation statements)

References 55 publications

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“…Aside from this, there are few examples on insulators where negative ion formation occurring directly from positive ions (i.e. simultaneous capture of two electrons), was found to be more likely than single electron capture from neutral atoms [55,56]. This has been explained with the above quasi molecular model including coulombic attraction and by the fact that the endothermic energy requirement associated to the neutralisation of the positive ion can be offset by the exothermic release of energy in populating the affinity level provided that they take place simultaneously.…”

Section: Negative-ion Surface Productionmentioning

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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Section: Negative-ion Surface Productionmentioning

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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“…There is a quite important literature on negative ion surface-production in wellcontrolled beam-experiments at grazing incidence (or low incidence angle), for a large variety of incident energy, various ion type and a large variety of surfaces, including caesiated (see for instance references 20, 21, 22, 23, 24, 25 and references therein) and non-caesiated surfaces (see for instance references 26,27,28,29,30,31,32,33,34,35, 36 and references therein). H-surface-production on Highly Oriented Pyrolytic Graphite (HOPG) or polycrystalline graphite has for instance been studied in 37, 38, 39 and 40.…”

Section: A-introductionmentioning

confidence: 99%

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

et al. 2012

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In previous works, surface-produced negative-ion distribution-functions have been measured in H 2 and D 2 plasmas using graphite surfaces (HOPG). In the present paper we use the SRIM software to interpret the measured negative-ion distribution-functions. For this purpose the distribution-functions of backscattered and sputtered atoms arising due to the impact of hydrogen ions on a-CH and a-CD surfaces are calculated. The SRIM calculations confirm the experimental deduction that backscattering and sputtering are the mechanisms of the origin of the creation of negative ions at the surface. It is shown that the SRIM calculations compare well with the experiments regarding the maximum energy of the negative ions and reproduce the experimentally observed isotopic effect. A discrepancy between calculations and measurements is found concerning the yields for backscattering and sputtering. An explanation is proposed based on a study of the emitted-particle angulardistributions as calculated by SRIM. A-IntroductionThe ITER project and its successor DEMO (first nuclear-fusion based power plant prototype) aim at demonstrating power production by magnetic confinement nuclear fusion. Plasma start-up and continuous operation in the case of a tokamak reactor require very efficient heating and non-inductive current drive systems. Neutral beam injection (NBI) which uses high power beams of fast neutral atoms of hydrogen isotopes to heat the plasma is a promising candidate. In most existing NBI systems on contemporary fusion experiments a beam of positive ions is extracted from a conventional ion source, accelerated to energies of the order of 100 keV and neutralized via charge exchange in a background of neutral hydrogen. Due to the much larger physical dimensions the NBI systems for both ITER and DEMO require neutral beam energies in the 1 to 2 MeV range where the neutralization of positive ions becomes very inefficient and only the negative ions can be neutralized with sufficient yield. Hence the development of high current negative ion sources (50A D-beam for ITER) is crucial to the development of the ITER and DEMO NBI systems. The highcurrent-density negative-ion source for ITER 1 is currently the subject of intense research

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“…30 and v Th ¼ 0.06 a.u. 40 ) and O-LiF(100) (v Th ¼ 0.1 a.u.) cases 27,29 is due to the relatively large valence band electron capture energy defect for our present H-LiF(100) collision system (see Fig.…”

Section: Electron Capture Probabilitymentioning

confidence: 99%

Negative ion formation by neutral hydrogen atom grazing scattering from a LiF(100) surface

et al. 2021

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F−formation via simultaneous two-electron capture during grazing scattering ofF+

Cited by 13 publications

References 55 publications

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

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

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

Negative ion formation by neutral hydrogen atom grazing scattering from a LiF(100) surface

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F−formation via simultaneous two-electron capture during grazing scattering ofF+

Cited by 13 publications

References 55 publications

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

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

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

Negative ion formation by neutral hydrogen atom grazing scattering from a LiF(100) surface

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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

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