摘要:

Surface processes are very important in the production of intense beams D−‐ions. This is obvious for the surface conversion sources. By using Ba as converter material current densities for H−‐beams exceeding 40 mA/cm2have been achieved. But also in volume sources surface effects are important, since the walls affect the vibrationally excited molecules and hydrogen atoms, which are very important components of the source plasma. In this report surface processes in the production of negative hydrogen ions will be discussed in the context of existing knowledge about these phenomena at the surface science level.

ISSN:0094-243X    

DOI:10.1063/1.39617

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Recent results of surface produced negative ions are presented. Two low work function metal surfaces have been studied, barium and magnesium, in combination with several plasma generators; RF‐ and DC‐filament discharges. The negative ion yield for barium is about 5 to 6 times larger than magnesium. This ratio is confirmed by model calculations on resonant charge exchange.

ISSN:0094-243X    

DOI:10.1063/1.39588

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Negative hydrogen ions are produced by backscattering a thermal distribution of hydrogen atoms from a converter surface coated with a mixture of cesium oxides. The thick film of cesium oxide is produced by thermal decomposition of cesium carbonate and subsequent thermal activation aided by atomic hydrogen. About 60% of atoms with energies greater than 1.5 eV are reflected as negative hydrogen ions for a temperature of 0.22 eV in the thermal distribution. The H−ions have a Maxwellian parallel energy distribution with a temperature equal to the atomic temperature. Replacing the thermal source of hydrogen atoms with a discharge source results in H−ions of 1 eV temperature and 100 times lower intensity.

ISSN:0094-243X    

DOI:10.1063/1.39602

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A report is given on recent crossed‐beams experiments studying single‐ and double‐electron removal from H−in energetic collisions with Arq+(q≤8) ions. The data is discussed with respect to conversion efficiencies of H−to neutral H0in plasma neutralizers proposed for efficient neutral beam heating of future fusion devices.

ISSN:0094-243X    

DOI:10.1063/1.39655

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Recombination of atomic hydrogen in a gas filled cell where the walls are covered with metal evaporated from either tungsten or tantalum filaments has been studied. The high internal energy (vibration) of the product H2molecule indicates that recombination occurs via a new mechanism. This mechanism involves the initial trapping of the H atoms in very weakly bound or physisorbed state on the top of the usual layer of strongly bound or chemisorbed layer of atoms which cover most metals when in presence of hydrogen.

ISSN:0094-243X    

DOI:10.1063/1.39624

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The relaxation of highly vibrationally excited H2molecules in gas‐phase and interacting with copper surfaces has been studied by using time‐dependent semiclassical models for the collisional dynamics. The best available potential for H2‐H2and H2‐Cu has been used in the calculations, and the most important features of the collisional interactions have been taken into account.

ISSN:0094-243X    

DOI:10.1063/1.39637

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

New sets of direct electron impact excitation cross sections involving vibrational excited states of H2(including dissociation, ionization andE‐Vprocesses) have been calculated by Gryzinski fomulation. These rates are then inserted in a numerical code based on the simultaneous solution of Boltzmann equation, of vibrational kinetics and H, H−production rates. Comparison of theoretical and experimental results shows satisfactory agreement for the electron temperature and electron density, while some discrepancy does exist on the negative ion concentration.

ISSN:0094-243X    

DOI:10.1063/1.39647

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Molecular vibrational excitation generated by recombination of molecular ions on barium electrode surfaces is presented. Negative hydrogen ion formation by vibrationally excited molecules rebounding from the surface is also calculated (AIP).

ISSN:0094-243X    

DOI:10.1063/1.39653

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Vibrational population distributions of hydrogen molecules generated in a hydrogen discharge have been calculated and compared with measured distributions. A five‐fold enhancement of the high vibrational levels with increased discharge current is discussed. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.39654

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this paper we have compared the energetics of three light molecules (H2, LiH and Li2) to form negative ions by the process of dissociative electron attachment. For two light homonuclear molecules (H2and Li2) we have done explicit calculations, using the local formalism of the resonance model, to obtain the electron attachment cross sections and the rates of negative ion formation.

ISSN:0094-243X    

DOI:10.1063/1.39603

出版商:AIP    

年代:1990

数据来源: AIP