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The evolution of a microsecond pulsed barrier discharge initiated in atmospheric pressure air in the point–plane electrode geometry has been investigated using streak camera photorecording and shadow photography with micrometer resolution and nanosecond exposure. It has been shown that the discharge develops in series and its structure evolves both within a series and from series to series. It has been found that, irrespective of the polarity of a feed voltage pulse, the discharge develops from the point electrode, having the form of a set of many micrometer-diameter channels. At the late stage, the discharge consists of a number of glowing microstructured channels, which occupy the space between the point and barrier and deviate from the point axis, and many faint channels radially propagating over the surface of the barrier. Numerical parameters of the structured have been obtained.

The results of studying the initial phase of a spark discharge microstructure formation in a tip–plane gap 1.5 mm length in air are presented. Measurements show that, within 15 ns after breakdown, the channel is an aggregate of a large number of microchannels, the current in the channel rises almost linearly to a value of 1 kA, and the electron density reaches 2 × 1019 cm–3. Calculations of the kinetics of processes in a separate microchannel taking into account experimental data have been carried out. It has been found that the average electron temperature ranges from 4 to 8 eV, the electric field strength is ~ 300 kV/cm, and electrical conductivity is ~10 Ω–1 cm–1. The results obtained show that it is the discharge microstructure that causes relatively high values of the average electron temperature along with a sufficiently high ionization degree.

The results of investigations of a spark discharge in air in the gap between the tip (anode) and a 1.5‑mm-long plane are presented. It is shown that, after breakdown, the discharge develops in the form of a beam of individual microchannels that close the discharge gap, then, after 20–30 ns, a continuous outer boundary of the channel forms and its radial expansion begins. The electron concentration at this moment reaches its maximum value at the level of 2 × 1019 cm—3. It was found that, starting from 60 ns, a cylindrical shock wave departs from the channel boundary. With time, the difference in the radii of the shock wave and the channel increases, resulting in the formation of a radial structure in the form of a highly conductive internal channel, separated from the shock wave by an intermediate shell. A computational and theoretical model is proposed to describe the dynamics of the spark channel expansion from the moment of the formation of a solid outer boundary, and a satisfactory agreement between the calculations and experimental data is obtained.

A spark discharge in a 1.5-mm-long tip (cathode)-plane gap in the time interval from the breakdown onset to 200 ns has been studied. Тhe discharge has been found to arise in the form of a bundle of microchannels. The dynamics of the discharge spatial structure, the electron concentration, the gas temperature in the channel, and the velocity of its radial expansion have been determined.

The results of studies of the dynamics of near-electrode processes in the initial phase of a spark discharge in atmospheric-pressure air in the point-plane geometry are presented. After breakdown, regions of about 50 μm or more in size with an increased electron concentration of (3–8) × 1019 cm–3 near the surface of the flat cathode have been observed. With allowance for the experimental data on erosion effect of the discharge on the surface of a flat electrode and the associated gas-dynamic effects, a physical model of near-electrode processes has been proposed, based on which the gas-dynamic parameters are estimated.

We have designed a device with a gliding unipolar arc of the Jacob’s ladder type. The dynamics of arc rising has been investigated. It is found that the arc climbs at a constant velocity on the major part of its path. The convective nature of the arc rise due to heating of air by the plasma is demonstrated. The dependence of the arc rise velocity on the opening angle between the electrodes is obtained. The dependence is found to be decaying.

Dynamics of the initial stage of discharge in air is studied at atmospheric pressure in a point–plane gap at different parameters of the tip electrode and lengths of the interelectrode gap. Spark or diffuse discharges are implemented in experiments depending on the length of the interelectrode gap. Shadow photography is used to show that, for all electrodes in the experiments, the discharge channels represent multiple microchannels that develop from the tip and close the discharge gap.

A microchannel structure of a spark discharge initiated in atmospheric-pressure air in a point–plane gap has been discovered by shadow photography. The structure has been observed since the onset of the discharge glow. The evolution of the microstructure over times from several nanoseconds to several tens of nanoseconds has been traced. Specifically, the development of microchannels from the point into the discharge gap, expansion of the microchannels, and their interaction have been observed. A correlation has been found between the microstructure of the spark channel in the discharge gap and its autograph on the surface of the plane electrode.

Observations of the early stage of a spark discharge in air at atmospheric pressure in the pin-to-plate geometry under a single high voltage pulse including an initial stage of the channel expansion are presented. It was shown that an interelectrode gap is closed by of a large number of microchannels at 20-30 ns. Start of a radial channel expansion is beginning at the moment when the electron concentration reaches the maximum value of 2*10^19 cm-3. Theoretical analysis based on proposed model takes the following plasma-channel properties: electric field strength is about several kV/cm, electron temperature is close to 2-3 eV, plasma conductivity is in the order of ~200 Ω-1•cm-1, speed of the radial spark channel expansion is about ~5 km/s.

The microchannel structure of a spark discharge in a 1.5-mm-long point–plane gap has been studied by the method of shadow photography. The discharge dynamics (propagation of microchannels from the point into the discharge gap, branching and expansion of the microchannels, formation of a joint front of the spark’s shock wave and its motion) has been observed over a time from several nanoseconds to several hundred nanoseconds. Objects of a half-ring shape have been discovered. They have been identified as semispherical shock waves resulting from the formation of microcraters near sites where the microchannels touch the plane electrode.

The results of studies of the microstructure in the initial phase of the discharge in air in the gap between the pin and a plane 1.5 mm long are presented. Measurements show that within 15 ns after breakdown, the channel is a bundle of a large number of microchannels, the current in the channel grows almost linearly up to 1 kA, and the electron concentration reaches 2 × 1019 cm−3. Taking into account the experimental data, the electron temperature dynamics in a separate microchannel was calculated. It was found that the average electron temperature is from 4 to 8 eV, the electric field strength is ∼300 kV/cm, and the electrical conductivity is ∼10 Ω−1 cm−1. The obtained results indicate that it is the microstructure of the discharge that determines the relatively high values of the average temperature of electrons in combination with a sufficiently high degree of ionization.

The dynamics of mechanical destruction of a conductor in an explosively formed fuse opening switch on a finned obstacle under the action of detonation products is studied in the injection channel of the U-70 proton synchrotron. Protonograms are recorded with digital multiframe electron-optic cameras. The exposure time per frame, about 30 ns, is determined by the duration of a proton bunch. The time from the beginning of motion of the conductor to its destruction is about 3 μs. It is shown that the switch with typical sizes of the obstacle (the thickness of the fin is 1.5 mm, and the width and depth of the groove are 1.5 and 4.5 mm, respectively) provides operation with satisfactory gasdynamic parameters.

Results are presented from interferometric studies of a coaxial injector operating in the nonsteady arc-discharge mode. The discharge was initiated and stabilized by pulsed gas puffing into the interelectrode gap of the injector. The dynamics of the plasma bunch formation and the spatial characteristics of the bunch are investigated, and the density of the generated plasma is determined.

A plasma opening switch fed by a helical magnetic explosion generator is developed. A plasma sheath with an axial length of ≈4 cm and an electron density of ∼1017 cm−3 is produced in the electrode gap of the switch by six coaxial gaseous-plasma injectors. A series of explosion experiments shows that the system developed allows one to study the switch at currents of about 2 MA.

A plasma injector with pulsed gas filling is investigated experimentally. Interferometric measurements of the formation dynamics of the plasma channel are carried out. Under optimal operating conditions, the injector is capable of producing a plasma channel 4 cm in diameter with an electron density of ∼1017 cm−3. The effect of the cathode diameter of the plasma opening switch on the conductivity of the plasma channel is studied. It is shown that the current flowing through the plasma channel of a single injector attains 400 kA.

Laboratory facility GITaRa-4 was put into operation for development of plasma current opening switch used in experiments with MCG powering on the program [1]. Capacitor storage, consisting of four pulsed current generators of 8 muF each and composite cable line, is used as a current source. Short circuit current is about 1.7 MA at rise time of 2.5 mus. Works on experimental development of plasma opening switch of megampere level with rise time of ~1 mus are started. To recalculate results of laboratory development for conditions of explosive experiments we have created and calibrated for well-known experimental data two- dimensional numerical method for POS operation in the framework of two-temperature Hall MHD model.

Summary form only given, as follows. Technology development of electrophysical high-power and high-energy density facilities requires contactless methods of their parameters recording. Optical diagnostics, which were successfully applied for investigations of plasma open switches technologies, belong to these methods. Plasma current open switches (POS) with the level of transmitted current up to 2 MA and storage time 1-2 ms are studied. Investigations were performed both with a laboratory model and an explosive experiment. Current measurements were performed with fiber-optical Faraday current probes. the knowledge of the plasma channel cross-section and its dynamic characteristics is important for understanding of the POS operation. Preliminary data of the plasma channel geometry versus time and velocities of its movement, obtained with a fiber matrix, are presented. Dynamic plasma characteristics were studied with a Michelson interferometer on the wavelength of a Helium-Neon laser and fast photorecorder with time resolution of 100 ns. The data of the linear electron density at an optimum plasma injector operating regime are obtained.

Progress made in technology of electrophysical machines of large capacity and high energy density require contact free methods for measuring their parameters. They include optical diagnostics that have been successfully applied for the study of plasma switch technology.

Summary form only given, as follows. The dynamic characteristics of plasma, flying out from injector to vacuum chamber of a plasma current open switch, are studied experimentally. Investigations were made using Michelson interferometer on the wavelength of He-Ne-laser (633 nm). Fast photorecorder FPR, operating in the regime of slit sweep with time resolution of 0.1 /spl mu/s, was used for recording of interference pattern. Plasma diagnostics was performed with two orientations of FPR slit-along plasma flux direction and perpendicular to it. Experiments have showed that free plasma electrons plays the main role in the change of refraction index. Error in determination of electrons linear density did not exceed 15/spl times/10/sup 15/ cm/sup -2/. Interferometer measurements show that at optimum operating regime plasma injector allows to create electron linear density of about 4/spl times/10/sup 17/ cm/sup -2/ in interelectrode gap. This corresponds to average electrons concentrations in the plasma column of 1/spl times/10/sup 17/ cm/sup -3/.