Study of the Ar metastable atom population in a hollow cathode discharge by means of a hybrid model and spectrometric measurements

Abstract

The role of the metastable Ar atoms in a 1-cm-diameter cylindrical hollow cathode discharge ͑HCD͒ is studied self-consistently based on a hybrid model and experimental measurements in the pressure range of 0.3-1 Torr and currents of 1-10 mA. The model comprises submodels based on the principles of Monte Carlo and fluid simulations. The Monte Carlo model describes the movement of the fast electrons, fast Ar and Cu atoms, and fast Ar + and Cu + ions as particles, while in the fluid model, the slow electrons, Ar + , Cu + ions, Cu, and Ar metastable atoms are treated as a continuum. The population of the two metastable states within the 3p 5 4s configuration ͑ 3 P 2 and 3 P 0 ͒ were combined into one collective level, for which the continuity equation was written. Typical calculation results are, among others, the two-dimensional profiles of the production and the loss rates of Ar metastable atoms, as well as the metastable atom densities and fluxes throughout the complete HCD. Moreover, the calculated radial profiles ͑averaged over the axial direction͒ of the Ar metastable atom density are compared with experimental radial density profiles recorded by laser absorption spectroscopy. The relative importance of the different processes determining the Ar metastable population is analyzed, as well as the influence of pressure and voltage on them. Experimental results evidence the presence of the metastable atom production source at the cathode surface, probably originating from fast Ar + ions and Ar atoms impinging on it. Comparison between experimental and calculated Ar metastable atom densities shows a good agreement at low pressures, but at 1 Torr the calculated values differ by a factor of 2 from the measured ones. Several possible explanations for this discrepancy are discussed.

Polishing of optical media by dielectric barrier discharge inert gas plasma at atmospheric pressure

“…Here, the possible underlying effects are electron quenching, twoand three-body collisions with argon atoms and Penning ionisation at the sample surface [12]. The existence of such species in the near-surface area can most likely be assumed due the direct plasma ignition on the substrate based on electron excitation and ion-impact excitation in the plasma sheath close to the sample surface [18] and/or resonant neutralisation. In the last case, argon metastables are provided as a result of the recombination of argon ions with the negative surface charge on the dielectric sample [19].…”

Model of microsecond pulsed glow discharge in hollow cathode for mass spectrometry

“…Processes in DC discharge in a HC were theoretically investigated in [35][36][37][38][39], millisecond pulsed discharges and afterglow were investigated theoretically in [40,41]. However, the significant instantaneous power of the microsecond PGD may lead to another picture of the basic processes in both the discharge and the afterglow, and a separate investigation of microsecond PGD is necessary.…”

“…Theoretical models for the simulation of a glow discharge in DC and RF modes for different applications have already been developed [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], typically a hybrid model is used. Processes in DC discharge in a HC were theoretically investigated in [35][36][37][38][39], millisecond pulsed discharges and afterglow were investigated theoretically in [40,41].…”

“…In this work we present a model of a microsecond PGD and its afterglow in HC, and the application of the model for the optimization of a developing commercial Time-of-Flight mass spectrometer "Lumas-30" [22][23][24]45] with HC PGD as an ion source. In the hybrid model [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] different submodels are used for simulation of different particles. To avoid difficulties with the combination of these submodels, we have developed another model based on the Monte-Carlo method for all particles in the discharge and continuity equations in the afterglow.…”

Computational study of sheath structure in chemically active plasmas

“…The chemical reactions and the corresponding rate constants were obtained from both the literature [7]- [13] and our own calculations. Some rate constants depending on electron energy distribution function (EEDF) were calculated using the computer program ELENDIF [14] which simulates the EEDF in the dependence on discharge parameters.…”