摘要:

In negative ion surface conversion sources with barium converters sputtering of hydrogenous surface particles is believed to be the dominant negative ion production mechanism. In the work performed at the FOM‐Institute ion sputtering is also used as cleaning and diagnostic tool. This paper will review the work related to the sputtering mechanisms applied in the FOM surface conversion experiment over the last years. It will be shown that not only sputtering but also direct reflection and prompt rebound sputtering contribute to the negative ion formation on a barium surface.

ISSN:0094-243X    

DOI:10.1063/1.44834

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Formation of negative ions as a result of the interactions of a heavy ion beam with a surface under coverage of an alkali element is calculated by developing a Monte Carlo simulation code. Discussions are made on the relation among the main parameters of the physical process. The effects of the incident ion energy and cesium coverage on velocity distribution of the sputtered atoms, and consequently the negative ionization efficiency, are calculated. The simulation results show good agreement with the available experimental results.

ISSN:0094-243X    

DOI:10.1063/1.44782

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Experimental data on generation of negative hydrogen ions on cesiated molybdenum surfaces are presented. The following processes are discussed: backscattering of protons and H2+ions, sputtering of adsorbed hydrogen by cesium ion bombardment, and backscattering of a thermal or superthermal distribution of hydrogen atoms. The data are compared with theoretical calculations. Surface production is an important process in most negative hydrogen ion sources. An example of a negative hydrogen ion gun using hyperthermal hydrogen atoms incident on an external converter is presented.

ISSN:0094-243X    

DOI:10.1063/1.44789

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Results of measurements of the total yield of H−ions due to surface conversion of H+and H2+ions at low work function surfaces are presented. A low energy (3–50 eV) ion beam strikes the target at normal incidence. All secondary charged particles are collected. Calculations of the theoretical negative ion yield as a function of incident perpendicular energy have been modified to include energy and particle losses due to scattering. The scattering is modeled using TRIM calculations of particle and energy reflection coefficients. A cosine distribution in scattering angle has been assumed. The surface investigated was polycrystalline molybdenum, cesiated by vapor deposition. The work functions were determined by measurements of photoemission threshold of these surfaces. H−and electron yields were determined by taking the ratio of the secondary charged particle currents to the proton current to the target. Secondary electrons were suppressed by a magnetic field. H−and electron yields of order 20% per incident nucleon were obtained.

ISSN:0094-243X    

DOI:10.1063/1.44836

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper demonstrates the production of H−ions by backscattering hyperthermal hydrogen atoms of energy 1–10 eV from a clean molybdenum and cesiated molybdenum surface. The total negative hydrogen ion yield for a Maxwellian distribution of the atoms has been estimated. The major production mechanism of hyperthermal hydrogen atoms has been described. Parallel energy distribution of H−ions has been measured in a uniform magnetic field for different discharge conditions. Experimental data for dependence of H−ion current on power and pressure have been presented. Finally, we have discussed the possibility of designing new type of high brightness H−ion source.

ISSN:0094-243X    

DOI:10.1063/1.44759

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Heavy negative ion production probabilities by Xe+sputtering on a cesiated sputtering surface were measured. The production probabilities were strongly affected by the cesiated surface condition which was determined by a flux of neutral cesium supply to the surface and a target surface temperature. The measured maximum production probabilities at the optimal condition were considerably high and were about 10% or more for Cu, C, Si, Ge, and W targets and about 1% for Ta and Mo targets.

ISSN:0094-243X    

DOI:10.1063/1.44812

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We report the results of simulating two multicusp volume negative ion sources in which plasma parameters, hydrogen vibrational spectra, and in one case the negative ion density, have been measured. We find generally good quantitative and qualitative agreement between experiment and theory for the basic discharge parameters. Good agreement is also found for atomic density, although the wall recombination coefficient &ggr;(H) is 0.05 in one source and 0.5 in the other. The calculated densities of vibrationally excited states with v‘≥5 are higher than the measured densities, but the calculated negative ion densities are lower than available measurements. Possible causes for these discrepancies are suggested.

ISSN:0094-243X    

DOI:10.1063/1.44822

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Measurements of plasma parameters, including electron density, electron energy distribution function (eedf), and negative ion density, have been made in the driver and extractor regions of a multicusp tandem ion source. Here results which focus on comparing operation in hydrogen and deuterium are presented. Several isotope effects are evident. In particular, for the same operating conditions, the electron density is found to be higher in deuterium than in hydrogen while the negative ion density is consistently lower.

ISSN:0094-243X    

DOI:10.1063/1.44804

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present a model of a ‘‘real’’ ion source and this model is compared with probe measurements made on two sources at Culham Laboratory.

ISSN:0094-243X    

DOI:10.1063/1.44776

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Effects of cesium vapor injection on H−production in a tandem source are studied theoretically by solving a set of particle balance equations in a steady‐state hydrogen plasma. In particular, enhancement of H−production and its mechanism, effects of wall recombination of H for surface H−production, and the effectiveness of the tandem two‐chamber system for H−optimization are discussed.

ISSN:0094-243X    

DOI:10.1063/1.44777

出版商:AIP    

年代:1992

数据来源: AIP