Subnanosecond pulsed X-ray source based on nanosecond discharge in air at atmospheric pressure

We have studied the characteristics of an X-ray source based on a gas diode filled with air at atmospheric pressure. Driven by a SLEP-150 pulser with a maximum voltage amplitude of ∼140 kV, a pulse full width at half maximum (FWHM) of ∼1 ns, and a leading front width of ∼0.3 ns, a soft X-ray source produces subnanosecond pulses with an FWHM not exceeding 600 ps and an exposure dose of ∼3 mR per pulse. It is shown that the main contribution to the measured exposure dose is due to X-ray quanta with an effective energy of ∼7.5 keV.     

A volume pulsed corona formed during nanosecond pulsed periodic discharge of negative polarity in narrow gaps with airflow at atmospheric pressure

A volume mode of spatially homogeneous nanosecond pulsed-periodic corona discharge of negative polarity has been obtained using an edge-to-edge electrode geometry in narrow gaps with airflow at atmospheric pressure and natural humidity. The parameters of discharge are estimated, and a factor limiting the power deposited in discharge is determined.     

X-ray emission from a low-current volume discharge in air at atmospheric pressure

The discharges in air gaps with cathodes of small curvature radius under the action of nanosecond high-voltage pulses have been studied. Low-current volume (diffused) discharge in air at atmospheric pressure is a source of x-ray emission. In the case of discharge with a low-intensity visible glow, x-ray emission takes place both from the gap and from the anode surface.     

On the possibility of generating volume dielectric barrier discharge in air at atmospheric pressure

A homogeneous volume dielectric barrier discharge (DBD) in air at atmospheric pressure and natural humidity has been obtained. Conditions ensuring generation of a homogeneous DBD are described. It is shown that a determining influence on the homogeneity of DBD is produced by the rate of electric field strength growth in the discharge gap.     

Nonlinear behaviors in a pulsed dielectric barrier discharge at atmospheric pressure

In this paper, the temporal nonlinear behaviors of pulsed dielectric barrier discharge in atmospheric helium are studied numerically by a one-dimensional fluid model. The results show that the common single-period pulsed discharge with two current pulses per single voltage pulse can take place over a broad parameter range. The rising and falling times of the voltage pulse can affect the discharge characteristics greatly. When the discharge is ignited by a pulse voltage with long rising and falling times, a single-period pulsed discharge with multiple current peaks can be observed. Under appropriate rising and falling times of the voltage pulse, a stable period-two discharge can occur over wide frequency and voltage ranges. Also this period-two discharge can exhibit different current and voltage characteristics with changing the duty cycle. With other parameters fixed, the pulsed DBD could be driven to chaos through period-doubling route by increasing either the falling time or the frequency of voltage pulse.     

Barrier open discharge at atmospheric pressure

A barrier open discharge operating under extremely hindered conditions is proposed, in which the working gas (helium) pressure admitting the electron beam formation can be increased up to 0.8 atm (more than ten times as compared to the usual open discharge) without any loss in stability. The anode grid (with 0.17 mm holes) was made separately and then placed on a dielectric substrate (ε ≈ 1000), but it can also be formed using vacuum deposition or photolithographic techniques. It is suggested that, by decreasing the diameter of holes in the anode grid, it is possible to provide for a stable discharge operation under still higher gas pressures.     

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.     

Prebreakdown stage of a surface discharge fired by a pulse in the air at atmospheric pressure

Results of investigation of a high-current plane pulsed surface discharge with separated torches fired in the air at atmospheric pressure are presented. The dynamics of ignition and development of the discharge in the prebreakdown stage has been considered. The main parameters of the plasma in the prebreakdown stage (the stage of intense prebreakdown glow) have been determined by spectroscopic methods and the influence of the dielectric material of a substrate on the plasma parameters has been analyzed. It has been established that the duration of an intense prebreakdown glow depends on the experimental conditions. A physical pattern of formation of an intense prebreakdown glow is proposed.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 1, pp. 178–185, January–February, 2005.     

A spherical microwave discharge induced at atmospheric pressure

A discharge induced at the end of an antenna in a flow of argon outgoing into the free space in a coaxial microwave plasmatron is described. Increased energy density supplied to the plasma leads to structuring of the microwave discharge. Effects of the antenna geometry, supplied power, and argon flow rate on the discharge structure are studied.     

Estimation of electron parameters in the dielectric barrier discharge with a liquid electrode at atmospheric pressure

In the oxygen dielectric barrier discharge (DBD) at atmospheric pressure, the current and voltage waveforms within the range of the mean-square voltages, 3.6–10.3 kV, and currents, 0.14–0.57 mA, were measured. The discharge burns in the glow regime. From the analysis of the equivalent discharge circuit, the voltage applied to the plasma was found. On the basis of these data, the reduced strength of the electric fields, E/N, was determined. From solution of the Botzmann equation for the electrons in the O₂-H₂O mixture, the electron distribution functions over the energies (EDFE) and certain electron parameters were found; the influence of presence of the H₂O molecules on those parameters was analyzed.     

Materials dynamics under nanosecond pulsed pressure loading

A nanosecond pressure pulse is generated by focusing a nanosecond-pulsed laser onto an aluminum target with plasma confined geometry. A spatially uniform pressure pulse is generated by focusing laser beams with a flat-top spatial energy distribution. High-pressure pulse loading and recovery experiments were performed on yttria-doped (3 mol%) tetragonal zirconia polycrystals at 11 GPa. In the pressure-loaded region, the monoclinic phase was uniformely formed. The transition ratio was approximately 30%. Nanosecond time-resolved Raman spectroscopy was performed on polytetrafluoroethylene under high-pressure pulse loading at 1 GPa, and rapid structural phase transition within 10 ns was revealed.     

Generation of subnanosecond electron beams in air at atmospheric pressure

Optimum conditions for the generation of runaway electron beams with maximum current amplitudes and densities in nanosecond pulsed discharges in air at atmospheric pressure are determined. A supershort avalanche electron beam (SAEB) with a current amplitude of ∼30 A, a current density of ∼20 A/cm², and a pulse full width at half maximum (FWHM) of ∼100 ps has been observed behind the output foil of an air-filled diode. It is shown that the position of the SAEB current maximum relative to the voltage pulse front exhibits a time shift that varies when the small-size collector is moved over the foil surface.     

Structure of RF capacitive discharge in swirl airflow at atmospheric pressure

Conditions for the onset of transitions between corona and pinch types of one-electrode radiofrequency capacitive discharges in swirl airflow at atmospheric pressure have been analyzed. It is established that the transitions observed at various values of the gas flow rate and swirl parameter are related primarily to the gasdynamic structure of airflow. Calculated data obtained in the framework of a proposed theoretical model are qualitatively consistent with the available experimental data.     

Surface modifications of polymethylmetacrylate films using atmospheric pressure air dielectric barrier discharge plasma

In this paper, polymethylmetacrylate (PMMA) films are modified using an atmospheric pressure non-thermal plasma generated by a dielectric barrier discharge (DBD) in air. The DBD is generated in a plane-parallel reactor, which is driven by a μs pulse power supply with amplitude of up to 25 kV and repetition rate of 1 kHz, and the plasma generated shows homogeneous mode discharge characteristics verified by electrical measurements and light emission images with 0.5 ms exposure time. The treatment time ranging from 0 to 60 s and the discharge power density ranging from 11.62 to 30.83 W/m² are used to study the effects of discharge parameters on the surface treatment, and the surface properties of PMMA films are studied using contact angle and surface energy measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM), fourier transformed infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The study shows that, after the plasma treatment, the surface of PMMA film is etched, and oxygen-containing polar groups are introduced into the surface. These two processes can induce a remarkable decrease in water contact and a remarkable increase in surface energy, and the surface properties of PMMA films is improved accordingly. It is shown that the improvement of hydrophobicity depends on the discharge power density and treatment time, and there is a saturation treatment time at each discharge power density. Increasing discharge power density can induce more effective treatment of PMMA films, and less treatment time is needed to achieve the same level of surface treatment by increasing the discharge power density. Because more oxygen-containing polar groups are created and more obvious etching is occurred on the PMMA surface at higher discharge power density.     

Thermodynamic parameters of butan-1-ol at atmospheric pressure

Published data are examined on the density, speed of sound, and isobaric specific heat of liquid butan-1-ol. Values have been calculated for the isochoric specific heat and the adiabatic and isothermal compression coefficients for the range 183.85-390.81°K.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 4, pp. 558–565, April, 1984.     

Mass spectrometer characterization of halogen gases in air at atmospheric pressure

We have developed a new interface for a commercial ion trap mass spectrometer equipped with APCI capable of real-time measurements of gaseous compounds with limits of detection on the order of pptv. The new interface has been tested using the detection of Br2 and Cl2 over synthetic seawater ice at atmospheric pressure as a model system. A mechanical pump is used to draw gaseous mixtures through a glass manifold into the corona discharge area, where the molecules are ionized. Analysis of bromine and chlorine in dry air show that ion intensity is affected by the pumping rate and the position of the glass manifold. The mass spectrometer signals for Br2 are linear in the 0.1-10.6 ppbv range, and the estimated 3sigma detection limit is 20 pptv. The MS signals for Cl2 are linear in the 0.2-25 ppbv range, and the estimated 3sigma detection limit is 1 ppbv. This new interface advances the field of analytical chemistry by introducing a practical modification to a commercially available ion trap mass spectrometer that expands the available methods for performing highly specific and sensitive measurements of gases in air at atmospheric pressure.     

Dynamics of the formation of pulsed transverse nanosecond discharge with prolate slot-cathode

Experimental studies of the spatial-time dynamics in formation and evolution of nanosecond plasma-beam discharge with a prolate slot-cathode in inert gases is investigated using a high-speed camera. Features and regularities in the dynamics of evolution of nanosecond discharge with the slot-cathode are established depending on the external conditions. As it has been shown experimentally, the first registered optical radiation of the discharge arises near cathode surface and the discharge formation starts simultaneously at the cathode slit output and between the electrodes.     

Characteristics of a high-enthalpy electric-arc heater for air at atmospheric pressure

A vortex-type plasma generator is described, and its current-voltage and heat characteristics as well as the basic parameters of the plasma jet are reported. Results of an investigation of the heater are compared with literature data. Correlations for the basic characteristics are derived that may be employed to design a high-enthalpy plasma generator.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 5, pp. 590–599, May, 1994.