Negative ion formation at a barium surface exposed to an intense positive-hydrogen ion beam

Journal Article · Sat Oct 15 04:00:00 EDT 1988 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.341340· OSTI ID:6831722

van Os, C F.A.; van Amersfoort, P W; Los, J

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.

• Research Organization: Association EURATOM-FOM, FOM-Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands
• OSTI ID: 6831722
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 64:8; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

640301* -- Atomic
Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKALINE EARTH METALS
ANIONS
ARGON IONS
BARIUM
BEAM PRODUCTION
BEAMS
BREAKDOWN
CATIONS
CHARGED PARTICLES
COLLISIONS
ELEMENTS
FABRICATION
FUNCTIONS
HYDROGEN 1 MINUS BEAMS
HYDROGEN IONS
HYDROGEN IONS 1 MINUS
HYDROGEN IONS 1 PLUS
ION BEAMS
ION COLLISIONS
ION EMISSION
ION SOURCES
IONS
METALS
PLASMA
WORK FUNCTIONS