Mikhail Pekker

Non-equilibrium nanosecond-pulsed plasma generation in the liquid phase (water, PDMS) without bubbles: fast imaging, spectroscopy and leader-type model

In this paper we report the results on study of the non-equilibrium nanosecond discharge generation in liquid media. Here we studied the discharge in both water and silicon transformer oil, and present our findings on discharge behaviour depending on global (applied) electric, discharge emission spectrum and shadow imaging of the discharge. We also discuss possible scenarios of non-equilibrium nanosecond discharge development and suggest that the discharge operates in a leader-type regime supported by the electrostriction effect—creation of nano-sized pores in liquid due to high local electric field.

Theoretical study of the initial stage of sub-nanosecond pulsed breakdown in liquid dielectrics

This paper presents a simple theoretical analysis of the initial stage of a sub-nanosecond pulsed high-voltage breakdown in liquid dielectrics. We show that a rapid breakdown is related to a rupture in the continuity of fluid induced by the electrostrictive forces in the inhomogeneous electric field in the vicinity of a needle electrode.

On the electrostrictive mechanism of nanosecond-pulsed breakdown in liquid phase

In this study we have studied the initial stage of the nanosecond-pulsed discharge development in liquid phase. Modelling predicts that in the case of fast rising strong nonhomogeneous electric fields in the vicinity of high-voltage pin electrode a region saturated with nanoscale non-uniformities may be developed. This phenomenon is attributed to the electrostriction mechanisms and may be used to explain development of breakdown in liquid phase. In this work, schlieren method was used in order to demonstrate formation of negative pressure region in liquids with different dielectric permittivity constants: water, ethanol and ethanol–water mixture. It is shown that this density perturbation, formed at the raising edge of the high-voltage pulse, is followed by a generation of a shock wave propagating with the speed of sound away from the electrode, with negative pressure behind it.

Investigation of positive and negative modes of nanosecond pulsed discharge in water and electrostriction model of initiation

This work investigates the development of nanosecond pulsed discharges in water ignited with the application of both positive and negative polarity pulses to submerged pin-to-plane electrodes. Optical diagnostics are used to study two main aspects of these discharges: the initiation phase, and the development phase. Nanosecond pulses up to 24 kV with 4 ns rise time, 10 ns duration and 5 ns fall time are used to ignite discharges in a 1.5 mm gap between a copper plate and a tungsten needle with radius of curvature of 25 µm. Fast ICCD imaging is used to trace the discharge development over varying applied pulse amplitudes for both positively and negatively applied pulses to the pin electrode. The discharge is found to progress similar to that of discharges in long gaps—long sparks—in gases, both in structure and development. The more important initiation phase is investigated via schlieren transmission imaging. The region near the tip of the electrode is investigated for slightly under-breakdown conditions, and changes in the liquids refractive index and density are observed over the duration of the applied pulse. An attempt to explain the results is made based on the electrostriction model of discharge initiation.

Initiation stage of nanosecond breakdown in liquid

In this paper, based on a theoretical model (Shneider and Pekker 2013 Phys. Rev. E 87 043004), it has been shown experimentally that the initial stage of development of a nanosecond breakdown in liquids is associated with the appearance of discontinuities in the liquid (cavitation) under the influence of electrostriction forces. Comparison of experimentally measured area dimensions and its temporal development were found to be in a good agreement with the theoretical calculations. This work is a continuation of the experimental and theoretical works (Dobrynin et al 2013 J. Phys. D: Appl. Phys. 46 105201, Starikovskiy 2013 Plasma Sources Sci. Technol. 22 012001, Seepersad et al 2013 J. Phys. D: Appl. Phys. 46 162001, Marinov et al 2013 Plasma Sources Sci. Technol. 22 042001, Seepersad et al 2013 J. Phys. D: Appl. Phys. 46 3555201), initiated by the work in (Shneider et al 2012 IEEE Trans. Dielectr. Electr. Insul. 19 1597–82), in which the electrostriction mechanism of breakdown was proposed.

Pre-breakdown cavitation nanopores in the dielectric fluid in the inhomogeneous, pulsed electric fields

This paper discusses the nanopores emerging and developing in a liquid dielectric under the action of the ponderomotive electrostrictive forces in a nonuniform electric field. It is shown that the gradient of the electric field in the vicinity of the rupture (cavitation nanopore) substantially increases and determines whether the rupture grows or collapses. The cavitation rupture in the liquid (nanopore) tends to stretch along the lines of the original field. The mechanism of the breakdown associated with the generation of secondary ruptures in the vicinity of the poles of the nanopore is proposed. The estimations of the extension time for nanopore in water and oil (polar and nonpolar liquids, respectively) are presented. A new mechanism of nano- and subnanosecond breakdown in the insulating (transformer) oil that can be realized in the vicinity of water microdroplets in nanosecond high-voltage devices is considered.

Pre-breakdown processes in a dielectric fluid in inhomogeneous pulsed electric fields

We consider the development of pre-breakdown cavitation nanopores appearing in the dielectric fluid under the influence of the electrostrictive stresses in the inhomogeneous pulsed electric field. It is shown that three characteristic regions can be distinguished near the needle electrode. In the first region, where the electric field gradient is greatest, the cavitation nanopores, occurring during the voltage nanosecond pulse, may grow to the size at which an electron accelerated by the field inside the pores can acquire enough energy for excitation and ionization of the liquid on the opposite pore wall, i.e., the breakdown conditions are satisfied. In the second region, the negative pressure caused by the electrostriction is large enough for the cavitation initiation (which can be registered by optical methods), but, during the voltage pulse, the pores do not reach the size at which the potential difference across their borders becomes sufficient for ionization or excitation of water molecules. And, in ...

Low Temperature Plasma Reforming of Hydrocarbon Fuels Into Hydrogen and Carbon Suboxide for Energy Generation Without

An alternative process of extracting energy from fossil fuels (coal, biomass, hydrocarbons, etc.) without the emission of CO2 is possible with nonequilibrium plasma. Apart from CO and CO2, there exists carbon suboxide (C3O2)-a solid carbon oxide, which can be polymerized to form chemically and thermodynamically stable substances. This article describes a novel process of extracting the energy from fossil fuels without the emission of CO2 while producing hydrogen and carbon suboxide (a reddish, brown polymer), an important constituent of organic fertilizers. This approach has the capability of avoiding drawbacks associated with combustion of fossil fuels, such as CO2 emission. The conversion processes of a hydrocarbon feedstock (n-butane) and characterization of the byproduct of the conversion process with energy dispersive X-ray spectroscopy are discussed. Thermodynamic calculation of energy efficiencies of conversion of readily available hydrocarbon feedstocks such as biomass, natural gas, and low quality coal (lignite and peat) into hydrogen and carbon suboxide is also discussed. Thermodynamic results calculated show energy efficiency of up to 78% for producing carbon suboxide from various hydrocarbon feedstocks when compared to energy efficiency of producing syngas (100%).

\hbox{CO}_{2}

Summary form only given. Plasma is best known as a gas phase phenomenon. Although efforts have been made in the past several decades to seek plasma in fluid phase, most researchers observed plasma only in low density phase (gas) bubbles and voids dispersed within fluids. Recent advances in pulsed power technology permitted application of much faster voltage rise times (including the subnanosecond range) and revealed that plasma-like phenomena can, in fact, occur in fluid phase quasi-homogeneously without any bubbles and voids1.