Electron collision rates in oxygen glow discharge

The calculations of the distribution function of electrons and the collisional rates were carried out on the basis of a numerical solution of the Boltzmann equation for a weakly ionized discharge in O₂ rangingE/N from 5 Td to 200 Td. The distribution function, Townsend ionization and dissociative attachment coefficients calculated were found to be in good agreement with experiments. A comparison of the results on the collisional rates with the values available in the literature was performed as well.     

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.     

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.     

A simple model of a glow discharge electron beam for materialsprocessing

A simple semiempirical model of the electron beam generated by a pulsed cold cathode electron gun has been developed. The model describes analytically the observed self-focusing of the discharge and predicts the dynamical variation of the focal distance, in good agreement with experiments. This effect plays a major role in the determination of the effective duration of the energy pulse. The model was used to conduct simple calculations of energy thresholds for melting of solid materials, giving helpful insight on ranges of operation of this kind of electron gun for its application to material processing. A comparison with available experimental data for Mg₇₀Zn₃₀ samples is given     

Role of nonlocal ionization in formation of the short glow discharge

An analytical model for estimating basic characteristics of short (without a positive column) glow discharges is suggested that allows for electron generation both in the cathode sheath and by nonlocal ionization in the plasma negative glow. The model is based on a previously developed approach according to which the discharge gap is divided into space-charge layers and a quasi-neutral plasma. The plasma region includes part of the negative glow, Faraday dark space, and positive column (if it exists). Simple expressions for basic characteristics of the glow discharge (I–V characteristic, cathode sheath thickness, position of the point of electric field reversal, etc.) are derived, and plasma concentration distributions are presented. The results obtained in terms of our model are in good agreement with experimental data, while local approximations based on the classical Engel-Steenbeck model diverge considerably from the experiment.     

Synthesis of nanoparticles in an atmospheric pressure glow discharge

Nanopowders are produced in a low temperature, non-equilibrium plasma jet (APPJ), which produces a glow discharge at atmospheric pressure, for the first time. Amorphous carbon and iron nanoparticles have been synthesized from Acetylene and Ferrocene/H₂, respectively. High generation rates are achieved from the glow discharge at near-ambient temperature (40–80°C), and rise with increasing plasma power and precursor concentration. Fairly narrow particle size distributions are measured with a differential mobility analyzer (DMA) and an aerosol electrometer (AEM), and are centered around 30–35 nm for carbon and 20–25 nm for iron. Particle characteristics analyzed by TEM and EDX reveal amorphous carbon and iron nanoparticles. The Fe particles are highly oxidized on exposure to air. Comparison of the mobility and micrograph diameters reveal that the particles are hardly agglomerated or unagglomerated. This is ascribed to the unipolar charge on particles in the plasma. The generated particle distributions are examined as a function of process parameters.     

Electron with anomalous moments in an electromagnetic field

In this paper the spin integrals of the motion are constructed for the generalized Dirac equation which describes an electron having anomalous moments. Using the spin integrals found, separation of the variables is carried out in the generalized Dirac equation. Exact solutions of this equation are found for the case of a constant, uniform electromagnetic field. The orthogonality and completeness of the system of functions obtained relative to a scalar product in the plane t=const is shown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 91–97, April, 1979.     

Electron beam induced formation of carbon nanorods

Electron beam induced formation of carbon nanorods was realized in situ under high resolution scanning electron microscopy (HRSEM). When a CVD deposited carbon nanotube sample was irradiated with an electron beam in an HRSEM, progressive etching of the sample, expanding of the nanotubes, and formation of additional nanorods have been observed. Transmission electron microscopy study revealed typical nanorods of 20 nm in diameter and with amorphous structure. The direct observation of the synthesis of nanorods under electron microscopy manifests the possibility of nano-machining of such nanomaterials using electron beams. This may lead to future integration and networking of nanostructures of different functionalities, which is crucial for nanotechnology.     

Stationary thread glow discharge

On the basis of new experimental results showing that a uniformly and slowly rotating regular thread is almost quasi-neutral and is difficult to influence by an external magnetic field, relations were derived which explain these phenomena. The angular frequency of rotation of a thread, derived from the equation of continuity, the equation for the momentum and from Poisson's equation, is dependent on the axial macroscopic velocity of negative ions, as has already been proved. At the same time conditions were obtained for the distribution of the space charge in the thread. It is seen that the quasi-neutrality is only very slightly disturbed.The author thanks G. Horváthová and P. Kocian from the department of physics of the electrotechnical faculty in Podbrady for some of the calculations and measurements.     

Initiation of a low-pressure glow discharge in a plasma electron source with a ribbon beam

Results are presented from an experimental investigation of a low-pressure glow discharge with a wedge-shaped hollow cathode in a plasma electron source, where this discharge is initiated by reflex and magnetron discharges. Zh. Tekh. Fiz. 69, 135–137 (July 1999)     

Spherical striations in a glow discharge

The stratification of a volume glow discharge is observed experimentally. Spherically symmetric stationary striations are detected. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 679–682 (10 December 1997)     

Electron energy distribution function in a hollow-cathode glow discharge in mixtures of nitrogen with electronegative gases

The electron energy distribution function (EEDF) in a hollow-cathode glow discharge in mixtures of nitrogen with electronegative gases is investigated. It is shown that small admixtures of SF₆ or CCl₄ to nitrogen significantly increase the number of electrons in the energy range 2–6 eV, which corresponds to the inverse part of the EEDF. In nitrogen with small admixtures of F₂ or NF₃, the EEDF differ slightly from that calculated for pure nitrogen. The EEDF in these mixtures substantially depends on electron attachment to electronegative gas molecules.     

Electron beam formation in a gas diode at high pressures

Electron beam formation in krypton, neon, helium, and nitrogen at elevated pressures are experimentally investigated. It is shown that, when the krypton, neon, and helium pressures are varied, respectively, from 70 to 760 Torr, from 150 to 760 Torr, and from 300 to 4560 Torr, runaway electrons are beamed at the instant the plasma in the discharge gap approaches the anode and the nonlocal criterion for electron runaway is fulfilled. The fast-electron simulation of discharge gap preionization is performed. The simulation data demonstrate that preionization in the discharge gap is provided if the voltage pulse rise time is shorter than a nanosecond under atmospheric pressure.     

Emission characteristics and parameters of a glow discharge in an argon-xenon-chlorine mixture

We present the results of a study of the emission characteristics of a low-pressure longitudinal glow discharge in an Ar-Xe-Cl₂ mixture (p = 0.5–6.0 kPa) and numerical modeling of its plasma parameters as a function of the parameter E/P. We optimized the average emission power of the discharge in the spectral range 160–310 nm as a function of the discharge current, the pressure and composition of the gas mixture. The plasma parameters were calculated for the optimal mixture (according to experimental data) and included obtaining the dependences of the electron transport and energy characteristics, the power losses per unit pressure in the discharge going toward elementary electron processes in the plasma, and also the ionization and attachment coefficients as a function of the parameter E/P. The results of numerical modeling of the glow discharge parameters allow us to provide a qualitative basis for the emission distribution in the spectrum of a plasma based on an Ar-Xe-Cl₂ mixture. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 563–567, July–August, 2008.