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  • 1
    Electronic Resource
    Electronic Resource
    Modeling of H− surface conversion sources; binary (H-Ba) and ternary (H-Cs/W) converter arrangements (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2575-2583 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The production process for the formation of H− ions in a surface conversion source is sputtering of hydrogen atoms from the converter surface layers by incident positive ions, followed by electron attachment via resonant charge exchange with the converter surface. The sputtering process is in direct relation to the converter surface composition. New experimental data led us to identify two different classes of converters: metallic converters, like solid barium(binary) and adlayer converters, like cesium on tungsten (ternary). For a binary converter the hydrogen in the surface layers is directly sputtered by the incoming ions. Consequently, the negative ion yield scales with the hydrogen concentration in the surface layers. In the cesium/tungsten system (ternary) the hydrogen at the surface is believed to be sandwiched between the cesium adlayer and the tungsten surface. Hence, the negative ion yield scales with the sputter coefficient of hydrogen on adsorbed cesium. This is experimentally confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349365
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  • 2
    Electronic Resource
    Electronic Resource
    Plasma-generator-induced effects on the dynamics of a negative-ion surface conversion source (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3485-3493 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The production of H− ions at a barium, magnesium, strontium, molybdenum, and lanthanum-hexaboride converter immersed in a hydrogen plasma have been investigated for pulsed and dc discharges. The scaling of the negative-ion output with incident positive-ion current on the converter depends greatly on the actual geometry and type of plasma generator. A less than linear scaling is observed in a multicusp system using filaments or rf to generate the discharge. A more than linear scaling is obtained in a configuration where the filament and the converter are separated by a permanent-magnet filter. For a rf plasma generator, there is a pronounced optimum in the relative position of antenna and converter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348489
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  • 3
    Electronic Resource
    Electronic Resource
    Development of a dc low pressure D− surface-conversion source using a 10-cm-diam solid barium converter : Proceeding of the fourth International Conference on Ion Sources (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2705-2707 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A D− surface-conversion source using a solid barium converter is designed for steady-state operation to produce 200 mA of D−. A similar ion source of twice the size as the one discussed here will meet the requirements set by the present US-ITER neutral beam injector design. Among the possible types of ion sources being considered for the US-ITER neutral beam design, the barium converter surface-conversion source is the only kind that does not use cesium in the discharge. This absence of cesium will minimize the number of accelerator breakdowns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142829
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  • 4
    Electronic Resource
    Electronic Resource
    Ion source metal-arc fault current protection circuit (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 3098-3099 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ion sources can be damaged by arcs between metallic components of the source if these arcs are permitted to last. The negative-biased low-work-function converter in a surface conversion negative ion source is especially susceptible to metal-arc breakdown damage. Here an electronic circuit for minimizing the damage caused by such an arc is described. The circuit uses a transistor switch and an inductor in series with the converter bias power supply to limit the damage during the metal-arc breakdown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142160
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  • 5
    Electronic Resource
    Electronic Resource
    H− enhancement process in a multicusp ion source operated with a barium insert structure (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1467-1469 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been demonstrated that the H− output current from a small multicusp source can be substantially enhanced if the hydrogen plasma is seeded with barium. Operating with a barium washer insert at the extraction aperture, it is found that the extractable H− current is increased by a factor of 3 if the insert bias potential is optimized. By use of a mixture of xenon and hydrogen gas, it is further demonstrated that the positive hydrogen ions are responsible for the observed H− enhancement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105199
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  • 6
    Electronic Resource
    Electronic Resource
    H− production from a barium converter with different discharge configurations (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 861-863 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The production of H− ions at a barium converter immersed in a hydrogen plasma has been investigated experimentally for a pulsed discharge. It is found that the scaling of the negative ion output with incident positive ion current on the converter depends greatly on the actual geometry of the plasma generator. A less than linear scaling is observed in a multicusp system. A more than linear scaling is obtained in a configuration where the filament and the converter are separated by a permanent magnet filter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103389
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  • 7
    Electronic Resource
    Electronic Resource
    Negative ion formation at a barium surface in contact with a hydrogen plasma (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1495-1497 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements on the production of negative hydrogen ions at a barium surface, in contact with a hydrogen plasma, are presented and discussed. In spite of the high work function of barium compared to more conventional cesiated converter surfaces, considerable yields of negative ions were produced. Conversion efficiencies up to 4% were achieved. No negative barium ions were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98613
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  • 8
    Electronic Resource
    Electronic Resource
    The role of cesium-ion bombardment in the formation of negative hydrogen ions on a converter surface (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5000-5011 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fundamental study of the formation of negative hydrogen ions via surface conversion is presented. Employed is a novel type of converter, namely a porous tungsten button with liquid cesium flowing through it towards the side which is in contact with the plasma. A high cesium coverage, i.e., a small work function, can easily be maintained with this approach. This is related to the high flux of neutral cesium atoms to which the converter is exposed and to the small cesium density in the discharge. Despite the small work function, we obtain negative-ion yields which are an order of magnitude smaller than is usually found in more conventional experiments, in which the converter is cesiated via injection of cesium vapor into the discharge. Furthermore, our energy distributions show that no negative ions are formed via desorption by cesium-ion impact. This gives a strong indication that the extracted negative hydrogen ions are primarily formed via this process in cesium seeded discharges. Our view is confirmed by the observation that the negative-ion yield increases with an order of magnitude when a small amount of argon gas is injected into the discharge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338320
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  • 9
    Electronic Resource
    Electronic Resource
    Negative ion formation at a barium surface exposed to an intense positive-hydrogen ion beam (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3863-3873 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fundamental study of the formation of negative hydrogen ions via surface conversion is presented. Employed is a novel type of converter, namely a pure barium metal surface. In spite of the high work function of barium compared to more conventional cesiated converters, considerable yields of negative ions were produced. Conversion efficiencies up of 4% are obtained, which is of the same order as for cesiated converters. The high negative-ion yield is probably related to the electron density of barium, which is almost twice that of cesiuim. This is confirmed by model calculations and by UHV scattering experiments under well-defined conditions. Furthermore, calculations showed that the hydrogen coverage of the converter increases with increasing flux of positive hydrogen ions to the surface. This behavior is confirmed experimentally. Seeding the hydrogen plasma with argon has no significant effect on the conversion efficiency. This is believed to be related to the competition between the lowering of the surface hydrogen coverage and the increase of the hydrogen desorption rate, both due to the higher sputter coefficient of argon compared to hydrogen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341340
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  • 10
    Electronic Resource
    Electronic Resource
    Transport of negative ions produced at a barium surface located within a multicusp ion source (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 539-546 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental study on the production of negative ions at a pure barium surface mounted in a multicusp bucket source is presented. The conversion efficiency, i.e., the ratio of the extracted negative-ion current and the positive-ion current incident on the surface, for deuterium and for hydrogen, have been measured as a function of source pressure, converter bias, and distance between conversion surface and extraction aperture. The conversion efficiency for deuterium is somewhat larger when compared to hydrogen. The conversion efficiencies obtained agree with a model, taking into account the concentration of hydrogen in the barium surface layers. The cross sections which were measured for the stripping of negative ions by neutral gas agreed well with values from literature. The experimentally determined divergence of the surface-produced beam was 4.5° for hydrogen and 3.6° for deuterium at an energy of 100 eV. At a source pressure of 5 mTorr, the volume-produced negative-ion current could be enhanced by 10%; for 1 mTorr this enhancement was of the order of 25%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140360
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