Negative ions, energy loss, and electron emission during grazing scattering of fast H and He atoms from a clean and oxidized NiAl(110) surface

Blauth, D.; Winter, H.

doi:10.1016/j.nimb.2010.11.051

Cited by 6 publications

(2 citation statements)

References 24 publications

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“…Furthermore, on the outgoing part of the trajectory, the electron loss back to the surface can be reduced or suppressed because no empty states are present in the band gap to recapture the electrons (figure 1d). Such models have explained that on LiF(100) surfaces, known to have one of the deepest valence band, yields of 10% Hhave been observed at grazing incidence 52,53 , more than one order of magnitude larger than from an Al surface 54 .…”

Section: Basic Mechanisms Of Negative Ion Formation At Surfacesmentioning

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: Basic Mechanisms Of Negative Ion Formation At Surfacesmentioning

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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“…Subsequently, these authors observed the efficient generation of a high negative-ion fraction when scattering on a MgO(100) crystal surface. [7] In 2011, Winter et al [8] also investigated the H − fraction on an oxidized NiAl(110) surface and found that the H − fraction was nearly one order of magnitude smaller than that on a LiF(001) surface. It was concluded for both alkali-metal halide and oxide surfaces that the wide band-gaps strongly suppress the electron loss from the formed negative ion back to the ionic surface, resulting in a high negative-ion fraction.…”

Section: Introductionmentioning

confidence: 99%

Landau–Zener model for electron loss of low-energy negative fluorine ions to surface cations during grazing scattering on a LiF(001) surface

Wang¹,

Zhang²,

Zhou³

et al. 2016

Chinese Phys. B

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There is no available theoretical description of electron transfer from negative projectiles at a velocity below 0.1 a.u. during grazing scattering on insulating surfaces. In this low-velocity range, electron-capture and electron-loss processes coexist. For electron capture, the Demkov model has been successfully used to explain the velocity dependence of the negative-ion fraction formed from fast atoms during grazing scattering on insulating surfaces. For electron loss, we consider that an electron may be transferred from the formed ionic diabatic quasi-molecular state to the formed covalent diabatic quasi-molecular state by the crossing of the potential curves of negative projectiles approaching the surface cations, which can be described by the Landau-Zener two-energy-level crossing model. Combining these two models, we obtain good agreement between the experimental and calculated data for the F − -LiF(001) collision system, which is briefly discussed.

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Plasma Electrode for Cesium-Free Negative Hydrogen Ion Sources

Sasao

Cartry

2023

Springer Series on Atomic, Optical, and Plasma Physics

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Negative ions, energy loss, and electron emission during grazing scattering of fast H and He atoms from a clean and oxidized NiAl(110) surface

Cited by 6 publications

References 24 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

Landau–Zener model for electron loss of low-energy negative fluorine ions to surface cations during grazing scattering on a LiF(001) surface

Plasma Electrode for Cesium-Free Negative Hydrogen Ion Sources

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Negative ions, energy loss, and electron emission during grazing scattering of fast H and He atoms from a clean and oxidized NiAl(110) surface

Cited by 6 publications

References 24 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

Landau–Zener model for electron loss of low-energy negative fluorine ions to surface cations during grazing scattering on a LiF(001) surface

Plasma Electrode for Cesium-Free Negative Hydrogen Ion Sources

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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

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