H− Formation in proton-metal collisions

Geerlings, J.J.C.; Amersfoort, P.W. van; Kwakman, L.F.Tz.; Granneman, E. H. A.; Los, J.; Gauyacq, J.P.

doi:10.1016/0039-6028(85)90640-5

Cited by 85 publications

(18 citation statements)

References 29 publications

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“…This could be caused by a decrease in H Ϫ production due to CsϪW coverage loading with energetic hydrogen ions. 3 The pollution of CsϩW coverage by a water leak increased the PG work function and stopped the replenishment flux to PG. It decreased the H Ϫ production down to about the pure hydrogen level.…”

Section: Discussionmentioning

confidence: 99%

Recovery of cesium in the hydrogen negative ion sources

Belchenko

Oka

Kaneko

et al. 2000

Review of Scientific Instruments

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Cesium recovery from the polluted layers in the 1/3 scale hydrogen negative ion source for LHD-NBI system has tested. It was found that the cesium recovery can be produced by additional discharges as from the cesium layer, aged by tungsten and residual gas, so as from the cesium layers, polluted by an occasional water leak. The highest cesium recovery to negative ion production was produced by a xenon arc, while glow discharge and arcing in hydrogen were less effective. The mechanism of recovery is the ejection of cesium from the underlying enriched layer by the arc and its transport to the surface.

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Section: Discussionmentioning

confidence: 99%

Recovery of cesium in the hydrogen negative ion sources

Belchenko

Oka

Kaneko

et al. 2000

Review of Scientific Instruments

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“…Until now, the dynamical resonant capture was only studied by perturbative methods [6][7][8] containing parameters that can be used in an adjustment procedure; in the H ~-Al case, these were found [8] to fail to reproduce the experimental results [5]. Recently, two methods [9,10] going beyond the perturbation level were developed to study the position and lifetime of atomic levels in front of metal surfaces.…”

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confidence: 97%

Dynamical resonant electron capture in atom surface collisions:H−formation in H-Al(111) collisions

1992

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The formation of H ~ ion by grazing-angle collisions of hydrogen on an Al(l 11) surface is investigated with the newly developed coupled angular mode method. The capture process involves a dynamical resonant process induced by the collision velocity. All the resonance properties of the H ~ level in front of an Al(l 11) surface are determined: position, width, and angular distribution of ejected electrons. The results are shown to account for the recent observations on H" formation by Wyputta, Zimny, and Winter. PACS numbers: 79.20.Nc, 34.70.+e Charge transfer between a moving atom and a surface is one of the fundamental aspects of the atom-surface interaction processes. Among these processes, the formation of an atomic or molecular negative ion during an interaction with a surface recently received a lot of experimental and theoretical attention [1]. Indeed negative ions have been invoked in quite a few different situations: charge transfer in atom-surface collisions [1], in particular in connection with the production of intense ion beams, resonant electron scattering by adsorbed molecules [2], desorption [3], and reactive scattering [4]; for all these processes the ion formation and destruction processes are of the greatest importance. Although the charge-transfer process has been the subject of numerous theoretical investigations, very few studies have been addressing this problem by quantitatively accurate methods.In the present paper, we report on the first nonperturbative parameter-free study of negative ion formation by dynamical resonant capture applied to the H-Al(lll) collisional system. The H electron affinity is much smaller than the surface work function and H ~~ formation by resonant capture should be inefficient. However, the experimental results of Wyputta, Zimny, and Winter showed that H " was formed in grazing-angle collisions [5], and this was interpreted as due to a dynamical resonant capture. Indeed, when the collision velocity parallel to the surface is important, one must take into account the effect of the frame transformation between the atom and the surface; this changes the energetical resonance condition and leads to a dynamical capture process.Until now, the dynamical resonant capture was only studied by perturbative methods [6-8] containing parameters that can be used in an adjustment procedure; in the H ~-Al case, these were found [8] to fail to reproduce the experimental results [5]. Recently, two methods [9,10] going beyond the perturbation level were developed to study the position and lifetime of atomic levels in front of metal surfaces. Since they did not take the dynamical resonance effect into account, their use was limited to studies of the charge-transfer process at low collision velocities. In the present work, we show that one of them, the coupled angular mode (CAM) method [10], can handle this dynamical effect which is very important for light negative ions as well as for systems with an electron affinity much smaller than the surface work function.The H ~ negative...

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“…6 An extensively studied combination is Cs/W͑110͒, used either with 0.6 monolayer or a full monolayer of Cs. [7][8][9] The WF shows a minimum of 1.45 eV for the submonolayer coverage and equals the value of bulk Cs ͑2.15 eV͒ for the full monolayer, which is far below the WF of bare W͑110͒ substrate of 5.25 eV. The same mechanism works for barium which has a bulk WF of 2.5 eV.…”

Section: Introductionmentioning

confidence: 77%

Metallic work function measurement in the range 2–3.3 eV using a blue light-emitting diode source

Schletti

Würz

Fröhlich

2000

Review of Scientific Instruments

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A new photoelectric method to monitor the work function of contaminated metallic surfaces in the range 2–3.3 eV using blue light-emitting diodes (LEDs) is presented. This method was specifically developed for an application onboard a spacecraft, where the simplicity of a system is a great asset. This technique makes it possible to follow the work function of a calibrated surface LED combination with a reproducibility of ∼2% with only one blue LED and a device to count photoelectrons. The surface described in this paper is Cs/W(110). The work function changes with time due to adsorption of residual gas in the moderate vacuum environment (in the mid 10−8 mbar range). Determination of the work function with a standard photoelectric technique is used to calibrate the system. We then derive calibration curves for this specific surface LED combination which reduce the workfunction measurement to a simple current measurement.

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H− Formation in proton-metal collisions

Cited by 85 publications

References 29 publications

Recovery of cesium in the hydrogen negative ion sources

Recovery of cesium in the hydrogen negative ion sources

Dynamical resonant electron capture in atom surface collisions:H−formation in H-Al(111) collisions

Metallic work function measurement in the range 2–3.3 eV using a blue light-emitting diode source

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