摘要:

Cross sections for the vibrational excitation of molecular hydrogen and its five heavier isotopes by the impact of low energy electrons are calculated using both the local and the nonlocal versions of the resonance model. It is demonstrated that, for a given incident electron energy, the cross sections for the vibrational excitation of heavier isotopes can be obtained from those of molecular hydrogen by a simple scaling procedure. It is seen that the scaling law holds for cross sections with values ranging over eight orders of magnitude.

ISSN:0094-243X    

DOI:10.1063/1.39604

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Experimental and theoretical electron energy distribution functions (EEDF) measured and calculated for the driver of a multicusp ion source operating in hydrogen are compared. The results indicate that atomic physics based theoretical models can accurately predict the EEDF in such discharges if some appropriate experimentally determined quantities are used as input parameters. The magnitude and shape of the EEDF is found to be particularly sensitive to the effective surface to volume ratio for electrons.

ISSN:0094-243X    

DOI:10.1063/1.39605

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have measured the energy distributions of H−ions produced by the collision‐induced dissociation process of H3+molecular ions in noble gas targets. The most probable H−c.m. energy was measured and over the energy range studied it was found to be dependent of the target species. Inelastic energy loss of 22±6 eV was measured and found to be the same for all cases.

ISSN:0094-243X    

DOI:10.1063/1.39606

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The role of LixHy(CsxHy) molecules, which can be formed from seeding an alkali into a hydrogen plasma, is examined throughab initiocalculations of the structure and stability of such species. The simplest alkali hydride, LiH, supports a bound anion for all internuclear separations. Larger structures, such as Li2H2and Li3H, do not support stable anions but exhibit thermodynamic stability as gas phase molecules. Their possible roles in dissociative attachment to form H−and/or Li−is examined.

ISSN:0094-243X    

DOI:10.1063/1.39607

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The recombination of triatomic hydrogen molecular ions and isotopomers thereof are important processes in the chemistry of negative ion sources. Recent measurements of the cross sections for these processes are reported.

ISSN:0094-243X    

DOI:10.1063/1.39608

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Influence of a discharge (up to 3A) on the vibrationally excited H2populations has been studied in a small hot filament source. Varying the intensity of the discharge and H2pressure in the gas cell, we observe a large increase of the lower vibrationally excited levels (v=1 to 4) whereas higher levels only undergo weak enhancement.

ISSN:0094-243X    

DOI:10.1063/1.39609

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A 7.8 A, 50 keV H−ion beam was produced by a cesium seeded volume negative ion source. The source consists of a 25 cm×46 cm rectangular multicusp plasma generator and a 14 cm×36 cm multiaperture extractor. Without cesium, the source produced 3.4 A, 75 keV H−ion beams. By seeding a small amount of cesium, we observed a big enhancement of H−production efficiency by a factor of four, and a reduction of optimum operating pressure. Extracted electron current decreased to almost zero when we biased the plasma grid positive with respect to the anode. The effect lasted for more than a week once the cesium was injected for several seconds at an oven temperature of 280–300 °C.

ISSN:0094-243X    

DOI:10.1063/1.39587

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A H−ion beam was produced by a cesium seeded discharge. The addition of cesium significantly increased the H−beam current. The cesium hollow cathode was introduced into the ion source with an axially symmetric geometry and radial magnetic feild. Influence of the accelerating voltage and the electrode width on the beam current was studied. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.39589

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We describe models for the long‐pulsed surface‐plasma multiaperture quasi steady‐state with a hydrogen negative ion output of up to 1 A, with an emission current density of 2 A/cm2, and with an average current density in a beam of 60 mA/cm2. The gas efficiency for the production of H−beams was 12–17%. The experimental and the simulated efficiencies of the negative ion production of pure hydrogen and cesiated surface‐plasma sources with geometrical focusing are compared.

ISSN:0094-243X    

DOI:10.1063/1.39590

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The negative ion density in a medium density, <5×1011cm−3, multicusp ion sources is found to be consistently lower in D2than H2. Under the same source operating conditions the plasma density in D2is found always to be higher than in H2. The effect of the different isotopes on transport processes in the discharge can be understood in terms of a simple model; however, the effect on molecular processes appears more complex.

ISSN:0094-243X    

DOI:10.1063/1.39591

出版商:AIP    

年代:1990

数据来源: AIP