Modeling of metastable argon atoms in a direct-current glow discharge

Abstract

To calculate the behavior of metastable argon atoms in a direct-current glow discharge, a balance equation is constructed, taking into account all known production and loss processes of the metastable atoms. Density profiles and cruxes of the metastable atoms are computed. The relative importance of different production and loss processes determining the metastable density is calculated for the case of a molybdenum cathode in pure argon. Besides electron-impact excitation, fast-ion and atom-impact excitation are found to be the dominant production processes at the high voltages used here, while loss of the metastable atoms is caused predominantly by diffusion and also by electron quenching to the nearby resonant states. The role of metastable atoms in the total discharge is investigated. They are found to play a minor role in the ionization of argon atoms, but their part in the ionization of sputtered molybdenum cathode atoms appears to be rather important. Moreover, they seem to have a significant effect on the secondary electron emission at the cathode. The investigation also includes the influence of pressure, voltage, and current on the metastable densities and f1uxes, on the relative importance of the different production and loss processes, and on the role of metastable atoms in the entire discharge.

Semianalytical description of nonlocal secondary electrons in a radio frequency capacitively coupled plasma at intermediate pressures

“…Actually recombination is important if n > (D abm =L 2 p ), where is the coefficient of the electron-ion recombination, and Lp = L0L sh . When the background gas is argon at p = 3 torr, Lp 3 cm, D abm 10 4 cm 2 s 01 , and 10 11 cm 03 s 01 [12] n must exceed the value 10 13-14 cm 3 , which is far beyond the explored range of densities discharge parameters are: frequency MHz, half of the gap cm, argon pressure torr. The constants which were used for the calculations are: electron mobility m /V/s (at 1 torr), gas heat conductivity W/(cm K), K. For discharges in helium and argon, the Townsend coefficient is typically approximated in the form where are constants [1].…”

Measurement of Excited Argon Atom in Glow Discharge Plasma by Diode Laser Coherent Forward Scattering Spectrometry (DL-CFS)

“…Consequently the absorption at 842.46 nm was dependent on the number density of metastable argon atoms. The production processes of metastable argon atoms are 11) (i) fast-electron-impact excitation from ground state argon atoms, including cascading from higher energy levels, (ii) fast-ion and fast-atom-impact excitation from ground state argon atoms, and (iii) radiative recombination between Ar + ions and slow electrons.…”

“…Ion-and atom-impact excitation, which is a very efficient process at high energies 12) leading to a very high production rate at the region close to the cathode where the ions and the atoms have high energies. 11,12) According to the Eq. (3), the number density of the produced metasatble argon atoms would be proportional to the total number of collisions between argon particles.…”

“…This is probably because the population density of argon metastable levels (11.55 and 11.72 eV) might be transferred to the nearby resonant state (11.62 eV) by collision with thermalized electrons, which is called electron quenching. 11) ... .................. (2) where m, r and * refer to a metastable state, a resonant state and an arbitrary excited state, respectively.…”

“…In the above processes, (ii) ion-and atom-impact excitation is dominant 11) ........ (3) where 0 refers to a ground state. Ion-and atom-impact excitation, which is a very efficient process at high energies 12) leading to a very high production rate at the region close to the cathode where the ions and the atoms have high energies.…”