Theoretical models of the negative ionization of hydrogen on clean tungsten, cesiated tungsten and cesium surfaces at low energies

Rasser, B.; Wunnik, John N.M. Van; Los, J.

doi:10.1016/0039-6028(82)90216-3

Cited by 149 publications

(60 citation statements)

References 20 publications

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“…The negative ion conversion yield could reach up to 20 percent for all production channels [13,14]. Therefore, the NI emission rate from the Cs covered plasma electrode surface was estimated ~7000A/m 2 .…”

mentioning

confidence: 99%

Numerical modeling of the Linac4 negative ion source extraction region by 3D PIC-MCC code ONIX

Mochalskyy¹,

Lettry²,

Minea³

et al. 2013

AIP Conference Proceedings

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At CERN, a high performance negative ion (NI) source is required for the 160 MeV H-linear accelerator Linac4. The source is planned to produce 80 mA of H-with an emittance of 0.25 mm mradN-RMS which is technically and scientifically very challenging. The optimization of the NI source requires a deep understanding of the underling physics concerning the production and extraction of the negative ions. The extraction mechanism from the negative ion source is complex involving a magnetic filter in order to cool down electrons' temperature. The ONIX (Orsay Negative Ion eXtraction) code is used to address this problem. The ONIX is a selfconsistent 3D electrostatic code using Particles-in-Cell Monte Carlo Collisions (PIC-MCC) approach. It was written to handle the complex boundary conditions between plasma, source walls, and beam formation at the extraction hole. Both, the positive extraction potential (25kV) and the magnetic field map are taken from the experimental set-up, in construction at CERN. This contribution focuses on the modeling of two different extractors (IS01, IS02) of the Linac4 ion sources. The most efficient extraction system is analyzed via numerical parametric studies. The influence of aperture's geometry and the strength of the magnetic filter field on the extracted electron and NI current will be discussed. The NI production of sources based on volume extraction and cesiated surface are also compared. Abstract. At CERN, a high performance negative ion (NI) source is required for the 160 MeV H -linear accelerator Linac4. The source is planned to produce 80 mA of H -with an emittance of 0.25 mm mrad N-RMS which is technically and scientifically very challenging. The optimization of the NI source requires a deep understanding of the underling physics concerning the production and extraction of the negative ions. The extraction mechanism from the negative ion source is complex involving a magnetic filter in order to cool down electrons' temperature. The ONIX (Orsay Negative Ion eXtraction) code is used to address this problem. The ONIX is a selfconsistent 3D electrostatic code using Particles-in-Cell Monte Carlo Collisions (PIC-MCC) approach. It was written to handle the complex boundary conditions between plasma, source walls, and beam formation at the extraction hole. Both, the positive extraction potential (25kV) and the magnetic field map are taken from the experimental set-up, in construction at CERN. This contribution focuses on the modeling of two different extractors (IS01, IS02) of the Linac4 ion sources. The most efficient extraction system is analyzed via numerical parametric studies. The influence of aperture's geometry and the strength of the magnetic filter field on the extracted electron and NI current will be discussed. The NI production of sources based on volume extraction and cesiated surface are also compared.

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mentioning

confidence: 99%

Numerical modeling of the Linac4 negative ion source extraction region by 3D PIC-MCC code ONIX

Mochalskyy¹,

Lettry²,

Minea³

et al. 2013

AIP Conference Proceedings

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“…The probability for this charge transfer process depends exponentially on the inverse of the work function of the converter surface [14]. A low work function is obtained by covering the inner surfaces of the ion source by a caesium layer with a thickness up to several monolayers (ML) [4,16,17].…”

Section: Physics Of Negative Hydrogen Ion Production In Iter Relevantmentioning

confidence: 99%

Modelling the ion source for ITER NBI: from the generation of negative hydrogen ions to their extraction

Wünderlich

Mochalskyy

Fantz

et al. 2014

Plasma Sources Sci. Technol.

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Abstract. The neutral beam injection system for ITER is based on a large (A source = 1.9 × 0.9 m 2 ) negative hydrogen or deuterium ion source. In this source negative ions are produced in a low-pressure (p fill ≈ 0.3 Pa) plasma by conversion of atoms and protons on a caesiated molybdenum surface with low work function. Then the negative ions are transported through the plasma to the extraction system where extraction of these ions and also co-extraction of electrons take place. This paper describes the status of the modeling activities connected with the negative ion test facilities of IPP Garching. It is illustrated that these modelling activities constitute a strong support of the experimental activities connected with the development of the negative ion source for ITER NBI. Several numerical codes developed in the past years -in close collaboration with the experiment -and their results are introduced. Focus is laid on the production, transport and extraction of negative hydrogen ions and on the inevitable co-extraction of electrons. Size scaling from the IPP prototype source to the ion source of the ELISE test facility to the full negative ion source for ITER NBI. Modeling the ion source for ITER NBI

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“…26,27 Thus, for a given scattering angle, the neutralization probability changes with the incident ion energy. As the energy decreases, the neutralization process becomes more adiabatic, which in the present case produces more neutrals since the work function of Fe ͑4.6 -5.1 eV͒ is smaller than the ionization potential of Li ͑5.39 eV͒.…”

Section: A Energy Dependence Of the Neutral Fractionmentioning

confidence: 99%

Internal electronic structure of adatoms on Fe(110) and Fe(100) surfaces: A low-energyLi+scattering study

2004

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The neutralization of 400-3000 eV 7 Li ϩ ions scattered from clean and adsorbate-covered Fe͑110͒ and Fe͑100͒ surfaces was measured with time-of-flight spectroscopy. Li singly scattered from bromine, iodine, and cesium adatoms has a consistently larger neutral fraction than that for scattered from substrate sites. This suggests that the local electrostatic potential directly above these adatoms is reduced from that of the clean substrate. The neutral fraction of Li scattered from halogen adatoms is surprising in that it decreases as the emission angle moves off-normal, yet increases in the usual manner for cesium and silver adatoms. This indicates that the charge distribution associated with a halogen adsorbate is nonuniform, most likely due to internal polarization. A semiquantitative theoretical analysis shows that a nonuniform internal electron density would give rise to the observed behavior. The polarization of halogen adatoms is likely responsible for anomalous work function changes observed previously. Alkali-ion scattering is shown to be an effective tool for detecting the internal electronic structure of an adatom.

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Theoretical models of the negative ionization of hydrogen on clean tungsten, cesiated tungsten and cesium surfaces at low energies

Cited by 149 publications

References 20 publications

Numerical modeling of the Linac4 negative ion source extraction region by 3D PIC-MCC code ONIX

Numerical modeling of the Linac4 negative ion source extraction region by 3D PIC-MCC code ONIX

Modelling the ion source for ITER NBI: from the generation of negative hydrogen ions to their extraction

Internal electronic structure of adatoms on Fe(110) and Fe(100) surfaces: A low-energyLi+scattering study

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