Energetic ion, atom, and molecule reactions and excitation in low-currentH2discharges: Spatial distributions of emissions

Abstract

Spatial distributions of H alpha , H beta , and the near-uv continuum emission from the H2 a ;{3}Sigma g;+ state are measured and compared with a model for low-current electrical discharges in H2 at high E/N and low Nd , where E is the spatially uniform electric field, N is the gas density, and d is the electrode separation. Data are analyzed for 300 Td<E/N<45 kTd , d=0.04 m , and 2 x 10;{21}<N<2.6 x 10;{22} m;{-3} . (1 Td=10;{-21} V m;{2}) The excitation is produced by electrons and by hydrogen atoms and molecules with mean energies from 5 to 1500 eV. Electron-induced emission, dominant at low E/N and low pressures, is distinguished by its buildup toward the anode. Excitation of H alpha by fast H atoms dominates at high E/N and increases toward the cathode. The observed H alpha emission at low E/N is normalized to previous experiments to yield absolute experimental excitation coefficients for all E/N and Nd . Small adjustments of model parameters yield good agreement with H alpha data. Cross sections are derived for excitation of the H2 near-uv continuum by H atoms. Spatial and pressure dependencies of H alpha and H2 near-uv emissions agree well with a model in which reactions of H2+ , H3+ , and H+ ions with H2 lead to fast H atoms and H2 molecules, which then excite H atoms or H2 molecules.

The cathode-fall of low-pressure hydrogen discharges: Absolute spectral emission and model

“…B 1 P þ u transitions of H 2 at positions near the cathode also appear to occur by this mechanism. 1,7 The data of Fig. 3(a) show a very similar behavior near the anode for all transitions.…”

“…Later models 13,14 include H þ , fast H, and fast H þ 2 and predict the spatial and pressure dependencies of the current and of the H a emission. 16,20 Of particular interest for present purposes are studies of the distribution of the electric field in the cathode fall of hydrogen discharges represented by Güntherschulze, 11 Warren, 12 Hantzsche, 16 Bederlow, 29 Renner et al, 17 Ganguly and Garscadden, 22 Barbeau and Jolly, 30 Czarnetzki et al, 27 Cvetanović et al, 26 and Pérez et al 31 The importance of diffuse reflection at the cathode of fast ions and neutral species as fast H atoms for low current H 2 discharges was shown by Petrović et al 2,7 and applied to models of glow discharges in H 2 by Cvetanović et al 26 and Phelps. 10 The stability of cathode fall dominated discharges in H 2 has been investigated experimentally and theoretically [3][4][5] for conditions similar to those of this paper.…”

“…As cited in previous papers of this series, [6][7][8]10 interest in the development and testing of more detailed kinetics models of the cathode fall in hydrogen results from the overlap of this work with the development of models for observations of Doppler broadening in other low pressure H 2 discharges, negative ion sources, inertial electrostatic confinement, planetary aurora, magnetically controlled fusion, and plasma processing schemes utilizing molecular gases.…”

“…These emission intensity results are placed on an absolute scale by reference to well established results for very low current (Townsend) discharges at moderate E=N, where E is the electric field and N is the H 2 density. The paper then examines the ability of a kinetics model, developed to predict quantitative emission probabilities and spectral profiles at low current densities, [6][7][8] to predict the spatial distributions of emission and electric field of the cathode fall and negative glow regions of moderate current discharges. In addition, this paper tests the proposal 1 that the spatially dependent behavior of electrons can be monitored by observation of the N 2 1st negative emission from N 2 -H 2 mixtures.…”

Influence of discharge conditions on energetic hydrogen atoms in a glow discharge

“…These distributions are especially important for comparison with the models, since they can be correlated to excitation coefficients. 28,36,37 The attenuation slope of the wide component (G3) is not significantly changed with pressure, and it is our opinion that the attenuation is predominantly determined by the wide angular spread from the surface backscattering process (see simulation in Ref. 25).…”