Mikhail A. Shulepov

Modification of the Near-Surface Layers of a Copper Foil under the Action of a Volume Gas Discharge in Air at Atmospheric Pressure

We have studied the modification of the near-surface layers of a copper foil under the action of a volume gas discharge, which was generated in air at atmospheric pressure by nanosecond high-voltage pulses of both negative and positive polarity applied between the foil and an electrode with a small radius of curvature. It is established that the surface layer of the discharge-treated copper foil in the central region is cleaned from carbon contaminations, while oxygen atoms penetrate in depth of the foil. The depth of a cleaned layer depends on the polarity of voltage pulses. For the positive voltage polarity on the foil, the cleaning takes place up to a depth exceeding 50 nm, while oxygen penetrates up to a depth of about 25 nm.

The formation of diffuse discharge by short-front nanosecond voltage pulses and the modification of dielectrics in this discharge

The dynamics of diffuse discharge formation under the action of nanosecond voltage pulses with short fronts (below 1 ns) in the absence of a source of additional preionization and the influence of a dielectric film on this process have been studied. It is established that the diffuse discharge is induced by the avalanche multiplication of charge initiated by high-energy electrons and then maintained due to secondary breakdowns propagating via ionized gas channels. If a dielectric film (polyethylene, Lavsan, etc.) is placed on the anode, then multiply repeated discharge will lead to surface and bulk modification of the film material. Discharge-treated polyethylene film exhibits a change in the optical absorption spectrum in the near-IR range.

Dynamics of the spatial structure of pulsed discharges in dense gases in point cathode−plane anode gaps and their erosion effect on the plane electrode surface

The dynamics of the spatial structure of the plasma of pulsed discharges in air and nitrogen in a nonuniform electric field and their erosion effect on the plane anode surface were studied experimentally. It is established that, at a nanosecond front of the voltage pulse, a diffuse discharge forms in the point cathode–plane anode gap due to the ionization wave propagating from the cathode. As the gap length decreases, the diffuse discharge transforms into a spark. A bright spot on the anode appears during the diffuse discharge, while the spark channel forms in the later discharge stage. The microstructure of autographs of anode spots and spark channels in discharges with durations of several nanoseconds is revealed. The autographs consist of up to 100 and more microcraters 5–100 μm in diameter. It is shown that, due to the short duration of the voltage pulse, a diffuse discharge can be implemented, several pulses of which do not produce appreciable erosion on the plane anode or the soot coating deposited on it.

UV and IR laser radiation's interaction with metal film and teflon surfaces

The interaction of Xe (λ ∼ 1.73 μm) and XeCl (0.308 μm) laser radiation with surfaces of metal and TiN-ceramic coatings on glass and steel substrates has been studied. Correlation between parameters of surface erosion versus laser-specific energy was investigated. Monitoring of laser-induced erosion on smooth polished surfaces was performed using optical microscopy. The correlation has been revealed between characteristic zones of thin coatings damaged by irradiation and energy distribution over the laser beam cross section allowing evaluation of defects and adhesion of coatings. The interaction of pulsed periodical CO 2 (λ ∼ 10.6 μm), and Xe (λ ∼ 1.73 μm) laser radiation with surfaces of teflon (polytetrafluoroethylene—PTFE) has been studied. Monitoring of erosion track on surfaces was performed through optical microscopy. It has been shown that at pulsed periodical CO 2 -radiation interaction with teflon the sputtering of polymer with formation of submicron-size particles occurs. Dependencies of particle sizes, form, and sputtering velocity on laser pulse duration and target temperature have been obtained.

Formation of superpower volume discharges and their application for modification surface of metals

Summary form only given. The results of experimental investigations of a volume avalanche discharge initiated by an e-beam (VADIEB) [1] and surface layer of Cu and AlBe foils modifications at the plasma action of VADIEB are given. The volume discharge in the air of atmosphere pressure formed in the gap with the cathode having small curvature radius and with high voltage pulses of nanosecond duration and positive and negative polarity. A supershort avalanche electron beam (SAEB [2]) with formation conditions in gases under atmospheric pressure have been investigated. It is proved that the surface layer is cleared of carbon at foil treatment, and atoms of oxygen penetrate into a foil. The cleaning depth depends on polarity of voltage pulses show. At positive polarity of a copper foil electrode, the cleaning is observed at the depth over 50 nm, and atoms of oxygen penetrate at the depth up to 25 nm. Plasma of the superpower volume discharge of nanosecond duration with a specific excitation power of hundreds of MW/cm3, and SAEB, and the discharge plasma radiation of various spectral ranges (including UV, VUV and X-ray) has the influence on the anode. The supershort avalanche electronic beam is generated only at negative polarity of a voltage pulse on an electrode with a small radius of curvature. SAEB influence on modifications of the copper foil surface is registered. VADIEB is easily realized in various gases and at various pressures, and, at gas pressure decrease, the density of the beam current in helium can achieve 2 kA/cm2 [3]. It allows predicting an opportunity of VADIEB application for metal surface modifications in various technological processes, and for surface dielectric modifications at the certain design of the anode.

Modification of water, aqueous solutions, and dielectric films in diffuse discharge formed by fast electron preionization at the short front of a voltage pulse

Formation of a diffuse discharge at a short front of voltage pulse (less than 1 ns), as well as when placing water, water solutions, and dielectric film inside the discharge, is studied. A volumetric discharge was observed in water on the anode when placing dielectric film (polyethylene, vinyl chloride-methyl methacrylate (VCMMA), etc.), water, or aqueous solutions of 3% hydrogen dioxide or 18% KMgO4 inside the discharge. The change in the absorption spectrum of substance was found after multiple discharge switching on. Fourier analysis of the infrared absorption spectra showed the difference between the spectra of exposed and unexposed polyethylene film. The changes in the absorption spectra of water, 3% hydrogen dioxide and 18% KMgO4 aqueous solutions are related with expansion of the band of valence oscillations of OH-groups without clearly expressed maxima (for the studied liquids). Therefore, volumetric diffuse discharge in molecular and atomic gases can be used in modifying dielectrics, water and aqueous solutions.

Application of diffuse discharges of atmospheric pressure formed by runaway electrons for modification of copper and stainless steel surface

The results of studies devoted to the influence of a runaway electron pre-ionized diffuse discharge (REP DD) formed in air and nitrogen at atmospheric pressure on the surface of copper and stainless steel are presented. Nanosecond high-voltage pulses were used to obtain REP DD in different gases at high pressures in a chamber with a flat anode and a cathode possessing a small radius of curvature. This mode of discharge was implemented owing to the generation of runaway electrons and X-rays. The conditions under which the surface of copper and stainless steel was cleaned from carbon and oxidized are described.

Effect of laser ablation on the mechanical impulse formation in capillary discharge plasma

Within studies on the creation of new types of engines for small-sized space vehicles, we have experimentally studied the effect of the laser ablation of an electrode (insulator) material on the mechanical impulse of capillary discharge plasma. It is demonstrated that laser pulses can be used to reliably initiate of lowvoltage capillary discharge at low pressures, that is, under conditions where the usual discharge initiation is complicated. The proposed combined scheme allows the weight and size characteristics of plasma thrusters operating in pulsed and pulse-train regimes to be reduced.

Formation of superpower volume discharges and their application for modification of surface of metals

Summary form only given. The results of experimental investigations of a volume avalanche discharge initiated by an e-beam (VADIEB) [1] and surface layer of Cu and AlBe foils modifications at the plasma action of VADIEB are given. The volume discharge in the air of atmosphere pressure formed in the gap with the cathode having small curvature radius and with high voltage pulses of nanosecond duration and positive and negative polarity. A supershort avalanche electron beam (SAEB [2]) with formation conditions in gases under atmospheric pressure have been investigated. It is proved that the surface layer is cleared of carbon at foil treatment, and atoms of oxygen penetrate into a foil. The cleaning depth depends on polarity of voltage pulses show. At positive polarity of a copper foil electrode, the cleaning is observed at the depth over 50 nm, and atoms of oxygen penetrate at the depth up to 25 nm. Plasma of the superpower volume discharge of nanosecond duration with a specific excitation power of hundreds of MW/cm3, and SAEB, and the discharge plasma radiation of various spectral ranges (including UV, VUV and X-ray) has the influence on the anode. The supershort avalanche electronic beam is generated only at negative polarity of a voltage pulse on an electrode with a small radius of curvature. SAEB influence on modifications of the copper foil surface is registered. VADIEB is easily realized in various gases and at various pressures, and, at gas pressure decrease, the density of the beam current in helium can achieve 2 kA/cm2 [3]. It allows predicting an opportunity of VADIEB application for metal surface modifications in various technological processes, and for surface dielectric modifications at the certain design of the anode.

Oxidation of titanium surface under laser irradiation

Formation of microscopic size colored dots on titanium foil surface by pulsed IR-laser irradiation was studied. It was found that the dot on titanium surface changes its color from yellow to blue as the exposure is increased. According to our numerical calculation, the colored dot formation is accompanying with titanium surface melting and partial evaporation. At pulse-periodical irradiation mode it can result in foil break-through.