摘要:

The concept of the tandem negative ion generator for producing hydrogen negative‐ion beams is reviewed. The dependence of negative‐ion density on electron energy, electron density, axial distance in the chamber and on the level of vibrational excitation is discussed. Possible applications to magnetic fusion are limited by current densities obtained. Optimization of current density by changing the scale length is discussed. (AIP)

ISSN:0094-243X    

DOI:10.1063/1.36543

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Electron energy distributions have been calculated for conditions representative of magnetic multicusp H2discharges. A moment approach has been adopted due to the dominance of electron‐electron collisions in the highly ionized plasmas considered. Results are presented for a 1–10 A discharge at 40 mTorr. Comparisons are made with numerical solutions of the Boltzmann equation and experiment. Satisfactory agreement is obtained at low energies E<5.0 eV. Scaling laws with discharge current are presented. Superelastic vibrational collisions are considered and found to have a minor influence on the distribution at all currents. The role of wall losses is examined and related to magnetic filter geometry.

ISSN:0094-243X    

DOI:10.1063/1.36558

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Electron ion recombination involving H12and H13has attracted considerable attention both from theoreticians and experimentalists in recent years. The status of these studies will be reviewed with particular emphasis on their role in elucidating negative hydrogen ion source chemistry.

ISSN:0094-243X    

DOI:10.1063/1.36539

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Electron excitation cross sections to produce vibrationally excited H2molecules are calculated for molecules initially in the first and second vibrational levels. The pattern of excitation cross sections as a function of final vibrational level v‘differs from that found in previous calculations initiated from the ground vibrational level.

ISSN:0094-243X    

DOI:10.1063/1.36548

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The role of H13(D13) ions in H2(v≥6) (D2(v≥9)) production in H−(D−) ion sources has been assessed. It is concluded that at most 4.6% of H13ions and 7.2% of D13ions contribute of H2(v≥6) or D2(v≥9) production in these plasmas. Based on previously established theoretical models this implies an additional contribution of about 15% to the overall production of highly vibrational excited molecules.

ISSN:0094-243X    

DOI:10.1063/1.36562

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The modeling of magnetic multicusp H2discharges is presented. The model is based on the coupling of the time‐dependent Boltzmann equation for the electron energy distribution function with the system of master equations for the H2vibrational excitation and kinetic equations for H and H−densities.The theoretical results given here are found to be in satisfactory agreement with available experimental ones and indicate, together with previous results, an extended validity range of the model.

ISSN:0094-243X    

DOI:10.1063/1.36570

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Computer simulated experiments, using the classical Monte‐Carlo trajectories, on the loss of negative ions by the process of mutual neutralization reveal that the neutral ambient gas particles enhance the rate of neutralilzation. A simple physical picture can explain this enhancement. A review of the traditional mutual neutralization and termolecular recombination processes is also provided.

ISSN:0094-243X    

DOI:10.1063/1.36580

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A survey of our current knowledge of measured dissociative attachment cross sections for the following processes is presented: i) dissociative attachment of electrons to the ground state of a molecule, ii) dissociative attachment of electrons to the rotationally, vibrationally, and electronically excited states of a molecule, iii) dissociative attachment of electrons to ultra cold molecules and molecular clusters, and iv) dissociative attachment to molecular radical species. Experimental techniques used in the measurement of the cross sections are brieflly described.

ISSN:0094-243X    

DOI:10.1063/1.36591

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The formation of negative ions in electrons scattering from a number of molecules (O2, CO, NO, N2O) condensed on a refrigerated polycrystalline platinum surface is reported in the energy range 0–20 eV. Two mechanisms namely, dissociative electron attachment and polar dissociation account for the observations. The behavior of the negative ion signal with thickness average as well as comparison with gas‐phase observations is discussed.

ISSN:0094-243X    

DOI:10.1063/1.36597

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The energy spectra of electrons detached in H−‐He collisions for H−energies up to 2keV have been measured directly at several angles using an electrostatic energy analyzer. There is a marked difference between these results and those obtained by both time of flight techniques and theory. At small angles spectacular structure is observed resulting from the decay of excited states of H−(resonances).

ISSN:0094-243X    

DOI:10.1063/1.36601

出版商:AIP    

年代:1987

数据来源: AIP