Formation of negative hydrogen ions on a cesiated W(110) surface; the influence of hydrogen implantation

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

doi:10.1063/1.335732

Cited by 31 publications

(17 citation statements)

References 24 publications

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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: 78%

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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Section: Introductionmentioning

confidence: 78%

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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“…For the first tests, the spectra have been analysed manually according equation (3). However for online monitoring of signals an automatic analysis routine is highly desirable.…”

Section: Discussionmentioning

confidence: 99%

“…Since in most cases n i << n k (gases and low temperature plasmas), stimulated emission is negligible. This means the density of the lower state of an atomic line and thus the ground state density for resonance lines is then directly accessible by (3) Concerning the two experimental setups discussed above, the white light absorption spectroscopy uses a continuum source with intensity I(λ,0) and the corresponding spectroscopic setup determines the measured line profile given by the apparatus profile Δλ app which results, due to the corresponding convolution of the line profiles, in a broadening of the absorption lines. For laser absorption the line width of the tunable laser is often much smaller than the Doppler width of the spectral line such that the absorption spectrum shows the Doppler broadening directly.…”

Section: Absorption Techniquementioning

confidence: 99%

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Optimizing the laser absorption technique for quantification of caesium densities in negative hydrogen ion sources

Fantz¹,

Wimmer²

2011

J. Phys. D: Appl. Phys.

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To cite this version:U Fantz, C Wimmer. Optimizing the laser absorption technique for quantification of caesium densities in negative hydrogen ion sources. Journal of Physics D: Applied Physics, IOP Publishing, 2011, 44 (33) Abstract. The performance of negative hydrogen ion sources, which rely on the formation of negative hydrogen ions on a surface with low work function, depends strongly on the caesium dynamics in the source. A quantitative measurement of the amount of caesium in the source during plasma-on and plasma-off (vacuum phase) is highly desirable. The laser absorption technique is optimized for the diagnostics of neutral caesium densities close to the extraction surface on which the negative hydrogen ions are generated. The setup has been simplified as much as possible utilizing also an automatic data evaluation for online measurements at high power rf sources. The setup has been tested and calibrated in a small scale laboratory experiment. The system and the analysis of the D 2 caesium line at 852.1 nm is described in detail, including effects of line saturation and density depletion. The system is sensitive in the density range of 10 13 -10 17 m -3 (path length of about 15 cm), allowing also for a temporal resolution of 40 ms. First very promising results from the negative hydrogen ion source are presented, such as the increase of the caesium density due to the caesium evaporation and time traces before, during, and after the discharge indicating a strong caesium redistribution.

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“…The work function of the bare plasma grid surface which is made of molybdenum-or tungsten-coated copper is above 4 eV. In this case only a negligible amount of negative ions is created by surface production [7]. At present, the operation of negative ion sources at ITER-relevant conditions is only possible by covering the plasma grid with an electropositive element like the alkaline metal cesium reducing its work function.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of the transport of ionic and atomic cesium in radio frequency-driven ion sources for ITER neutral beam injection

Gutser

Wünderlich

Fantz

et al. 2011

Plasma Phys. Control. Fusion

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Abstract. The neutral beam injection heating system of the future ITER fusion experiment will rely on the acceleration and neutralization of negative hydrogen ions. Cesium seeding into negative ion sources is a prerequisite to obtain the required ion current at a maximum pressure of 0.3 Pa and a tolerable level of co-extracted electrons. Both the stability and the delivered current density of the ion source depend highly on the cesium conditions of the production surface during plasma and vacuum phases. The Monte Carlo code CsFlow3D was developed and applied to simulate the distribution and time dynamics of neutral and ionic cesium during long pulses of the IPP prototype RF-driven ion source. These transient simulations show that the release of cesium accumulated within the ion source during the operation phase is the dominant mechanism to obtain cesium flux onto the production surface for negative ions (plasma grid). Studies of the spatial distribution of the deposits and the corresponding time dynamics and cesium flux profile are presented during long pulses. These show that the cesium flux onto the plasma grid has a high time variation which is a consequence of the transient release of reservoirs. While a high ionic flux is generated within the first seconds of the discharge, a broad neutral-dominated flux peak evolves during the total pulse interval.

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Formation of negative hydrogen ions on a cesiated W(110) surface; the influence of hydrogen implantation

Abstract: The formation of a negative hydrogen ion beam by surface conversion of a positive ion beam on cesiated tungsten surfaces Summary Abstract: Sputtering of negative carbon ions from cesiated graphite surfaces

Cited by 31 publications

References 24 publications

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

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

Optimizing the laser absorption technique for quantification of caesium densities in negative hydrogen ion sources

Dynamics of the transport of ionic and atomic cesium in radio frequency-driven ion sources for ITER neutral beam injection

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