Gas dynamics and thermal-ionization instability of the cathode region of a glow discharge. Part I

A model of the cathode sheath of a glow discharge is developed. The model includes the equations for calculating the non-steady-state nonequilibrium physicochemical gas dynamics, cathode temperature, and electric field. The model applies to describing the flow of a viscous, heat-conducting, moderately rarefied gas at Knudsen numbers of about Kn ∼0.03. The electric field and gas density distributions are determined consistently by renormalizing the values obtained by the Engel-Steenbeck theory. A formula for calculating the time during which a homogeneous volume discharge phase exists is proposed. The formula is based on the relation between the rates of electron production via associative ionization (A+B → AB ⁺+e) and impact ionization (A2+e → A ₂ ⁺ +e+e). Calculations are carried out for nitrogen and air. It is shown that, at high current densities, due to the dissociation and strong heating of the gas, the rate of thermal ionization becomes as high as that of electrical ionization. The calculated ionization time is in reasonable agreement with the measured duration of a uniform anomalous cathode sheath.     

Effect of negative glow on the elementary processes occurring in the cathode region of a glow discharge

The role of the negative glow in producing charge carriers and the effect of this region on the elementary processes occurring in the region of cathode potential drop between plane parallel electrodes is considered in this paper.An estimate of the value of positive ion current passing to the cathode from the negative glow is made for nickel, copper, iron, and aluminum cathodes in hydrogen, and for an iron cathode in argon neon, and helium at 1 mm Hg pressure.Based on the values obtained for the ion current in the Crookes dark space, the electric field intensity and potential distributions are calculated and found to be in satisfactory agreement with the experimental data.     

Resonance radiation in the cold cathode region of a glow discharge in argon

The imprisonment of resonance radiation in the cold cathode region of a glow discharge in argon is calculated. It is shown that the number of resonance photons reaching the cathode surface is substantially smaller than the number of positive ions.     

Distribution of plasma parameters in the cathode region of a glow discharge in nitrogen

The experiments with a low-pressure glow discharge in nitrogen indicate the formation of a potential well for thermal electrons and the sign reversal of the electric field near the concentration maximum of the near-cathode plasma. Depending on reduced discharge length pL, one or two field reversal points exist, which correlate with the sign of the anode fall (negative or positive, respectively).     

Spectroscopic investigation of the cathode region of an independent glow discharge in He

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 203–207, August, 1989.     

The excitation of spectral lines in the cold cathode region of a glow discharge in argon

Calculations on the excitation of spectral lines emitted by the cathode fall and the negative glow regions of a glow discharge in argon have been performed using space-dependent electron velocity distributions allowing for electron impact excitation and ionization of atoms.     

Controlled propagation of a glow discharge along a divided cathode

Conclusions With the gas-discharge device used, propagation of a glow discharge along a divided cathode, making use of -processes, is a quite reliable and well-reproducible process.Neighboring discharge gaps are reliably isolated when there is a positive potential on the controlled electrode, and reliably connected when this potential is negative.The shape of the discharge gap and the effective role of the control electrode combine to shorten the discharge-formation time and the discharge-gap deionization time.As the discharge travels in our device, there is a bright, linear optical trace (see Fig. 2). This method of glow-discharge propagation can find widespread, effective application in cold-cathode gas-discharge devices for signal conversion in pulse equipment.     

Non-local model of hollow cathode and glow discharge

A general form of the non-local equation for an ionization source in glow discharge and hollow cathode 3D-simulation is formulated. It is a fundamental equation in hollow cathode theory, which allows formulation of a complete set of field equations for a self-consistent problem in a stationary glow discharge and hollow cathode. It enables us to describe the region of negative glow and the hollow cathode effect and compare calculation results of electrical dependencies (pressure-voltage) with experimental data, – under conditions of gradual appearance of the hollow cathode effect.     

Gas dynamics of a supersonic radial jet. Part II

The paper presents the radial distributions of the pressure measured with a Pitot tube for the case of a radial jet with/without swirling of the input flow in the pre-chamber; the length of the supersonic part of the jet, dependency of the jet thickness as a function of the distance from the nozzle outlet, and approximating analytical formula for the jet thickness that generalizes the experimental data. Experimental data demonstrated that at the deposition distances lower than 4-6 gauges from the nozzle outlet, the solid particle velocity and temperature are almost uniform over the jet cross section. This means that the target surface can be allocated here without loss in coating quality and deposition coefficient. The maximal recommended distance where the deposition is still possible is the length of l _s0 ~ 16 gauges.     

Spectropolarization investigations of the region of the cathode drop in the potential of a helium glow discharge at atmospheric pressure

The dimensions of the region of the cathode drop in potential in a helium glow discharge at atmospheric pressure (in Kiselevskii’s plasma source) are determined. Using Stark spectroscopy of the Balmer-series hydrogen line H_β the spatial distribution of the constant and variable components of the electric-field strength is measured. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 362–368, May–June, 1999.     

Electric field in cathode layer of anomalous glow discharge

The cathode layer of anomalous glow discharge is calculated taking into account in a kinetic approximation the resonance charge transfer of ions emitted by the negative-glow plasma. The results of calculation of the electric-field distribution are in good agreement with experiment for a discharge potential in the kilovolt range.Kiev Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, Nos. 3, 4, pp. 363–367, March–April, 1992.     

A model of the cathode spot glow discharge for a cathode withinclusions of low work function material

A model that describes the self-maintained glow discharge for a composite cathode in which cathode spots are formed on low work function material inclusions is presented. Based on this model, expressions are obtained for the radius of the spot, the cathode voltage, and the spot current as functions of Pd (where P is the gas pressure and d is the thickness of the cathode layer), the parameters of the inclusions, and the basic material matrix are obtained. Numerical results for the case of a glow discharge in 75 torr neon gas with a copper cathode matrix and inclusions of LaB₆ are presented. The average radii of inclusions were 0.05 and 0.015 mm. Conditions under which the glow discharge migrates from the inclusions and begins to spread onto the surface of the basic matrix are obtained. The transition of the glow discharge into a contracted state, depending on the structure of the composite material, is also considered     

Electron impact ionization and excitation rate coefficients in the negative glow region of a glow discharge

Some easy to use reasonable approximations for electron impact rate coefficients have been considered. The most important rate coefficients for electron collisions in noble gases are electron-neutral ionization and electron impact excitation. Electron-neutral ionization besides electron impact excitation of some states of the argon and helium atom in direct current (dc) glow discharge plasma has been calculated. The plasma parameters of electron are significant factors for computing the rate coefficients. We present first results of probe diagnostic that includes the double probe measurements of the plasma parameters, namely, electron temperature (T_e) and electron density (n_e). Electron properties obtained from the double probe characteristic curves including T_e and n_e as well as the calculated rate coefficients (ionization and excitation) were studied as a function of the axial distance from the cathode while the discharge operating parameters of voltage and pressure were varied. Two regions of the glow discharge were investigated: cathode fall region and negative glow. Particular emphasis was placed on the negative glow region.