The radial structure of a steady-state surface-wave-sustained cylindrical argon plasma submitted to a static, axial magnetic field is described in the context of a hydrodynamic model using three-moment equations for electrons and two-moment equations for ions. This plasma model is coupled self-consistently to Maxwell’s equations and yields the radial profile of the electron density and temperature, as well as the radial distribution of excited species, in the 3p56d orbital configuration of argon. In this paper, the discussion focuses on the radial structure of the plasma as a function of the operating conditions (magnetic field intensity, gas pressure, wave frequency, plasma tube radius). It is found that the electron density profile is, generally, weakly modified, as these parameters are changed. In contrast, the electron temperature profile and, consequently, the excited atom density distribution are very sensitive functions of the operating conditions.
High intensity discharge (HID) lamps are often initiated by the application of one or more short, high-voltage, breakdown pulses superimposed on a 50 or 60 Hz generator voltage. A successful transition from the breakdown event to steady-state operating conditions in HID lamps requires that the lamp-circuit system be adequate to sustain the plasma created during breakdown until the electrodes are heated to thermionic temperatures. In this article, we use a one-dimensional (in the axial direction) transient discharge model to study the conditions needed to sustain the cold-cathode discharge after a breakdown event has occurred. While the application of our one-dimensional model to real lamps is approximate, we find that the model predictions are consistent with experimental results in HID lamps, a few of which are presented here. The main conclusion from this work is that, after breakdown, the voltage necessary to sustain a glow discharge is dependent on the source impedance, the gas composition, and on the plasma density created by the breakdown event.
Simple analytical representations of the ionization source terms in argon, helium, nitrogen, and silane dc glow discharges for steady-state and quasisteady-state conditions are presented. These analytical forms express well the highly nonequilibrium nature of the ionization in the cathode fall and negative glow regions which cannot be described by a Townsend ionization coefficient depending on the local value of the reduced electric field. These source terms can be easily incorporated into fluid models of gas discharges.
Regular oscillations in the current are predicted in low-pressure, planar discharges under certain conditions in electronegative gas mixtures in which the attachment rate coefficient is large at low values of E/P, the ratio of the electric-field strength to the gas pressure. The frequency of the oscillations is about 10 kHz, and depending on the conditions of pressure, gap spacing, and applied voltage, the current wave form varies from a near-sinusoidal shape to regularly repeating and well-separated spikes with a peak current density on the order of or less than 1 mA/cm2. The instability which gives rise to these oscillations is due to attachment, and the oscillations result from alternate phases of space charge buildup and decay. Thus, the current oscillations predicted here in planar discharges are analogous to Trichel pulses, periodic current spikes which are observed in negative point-plane corona discharges in electronegative gases.
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