Oxidation of a galenite surface under the impact of nanosecond pulses

The effect of high-voltage nanosecond pulses on the phase composition of a galenite surface is investigated by means of XPES and IR Fourier spectroscopy. According to the XPES data, structural-phase transformations caused by pulsed treatment are mainly associated with variations in the chemical state of sulfur atoms, which determines the electrochemical and flotation properties of a semiconductor sulfide mineral: an increase in the electrode potential creates favorable conditions for adsorption of anion collectors and raises the flotation activity of galenite.     

Modifying the physicochemical and electrical properties of tantalite and columbite surfaces under conditions of electrochemical treatment and high-voltage nanosecond pulses

Structural and chemical modifications of tantalite and columbite surfaces, induced by treating the minerals with anolyte—a product derived via the electrolysis of aqueous solutions—and high-voltage electromagnetic pulses, are studied by means of X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscopy, and electrophoretic light scattering. The mechanical properties of the surfaces are characterized via Vickers microhardness testing. Treating the minerals with anolyte removes iron-containing surface films and leads to considerable conversion of surface-confined Fe(II) species into Fe(III), increasing the differences between the physicochemical and electrical properties of these rare earth minerals. The nonthermal impact of high-voltage pulses results in effective surface softening, a reduction in microhardness, and the disintegration of mineral particles, yielding surface micro- and nanosized phases enriched with iron and oxygen.     

Nanosecond electrical discharges between semiconducting sulfide mineral particles in water

A model for developing electric discharges between sulfide mineral (pyrite) particles under high-voltage nanosecond pulses in a liquid medium (water) is considered. A possibility of electrical breakdowns of liquid gaps between particles under nanosecond pulses is shown. This probability and the energy released in discharge channels depend strongly on the sulfide conductivity.     

On the characteristic properties of oxidation of sulfide minerals exposed to nanosecond electromagnetic pulses

High-power nanosecond electromagnetic pulses cause changes in the chemical and phase surface composition of sulfide minerals (pyrrhotite and pentlandite) and their sorption, flotation, and chemical activities. The influence of the conditions and parameters of the electric-pulse effect on the change in the amount of elemental sulfur and iron oxide on the surface of mineral particles, as well as the concentration of iron and sulfoxide ions in the aqueous mineral suspension, has been studied. The parameters of preliminary pulsed treatment of pyrrhotite and pentlandite that lead to improvement of flotation separation of minerals have been determined.     

Nanosecond discharge in sulfur hexafluoride and the generation of an ultrashort avalanche electron beam

A discharge in the presence of a nonuniform electric field and the generation of an ultrashort avalanche electron beam (UAEB) are studied in the insulating gas SF₆ at the pressures 0.01–2.50 atm. High-voltage nanosecond pulses (about 150 and 250 kV) and the voltage pulses with an amplitude of 25 kV and a duration of tens of nanoseconds are applied across the gap. An electron beam is obtained behind the AlBe foil with a thickness of 45 μm at a sulfur hexafluoride pressure in a gas-filled diode of up to 2 atm. It is demonstrated that, at relatively high pressures (greater than 1 atm) and in the presence of high-voltage nanosecond pulses across the gap, the UAEB pulse FWHM increases. The spectra of the diffuse and contracted discharges in sulfur hexafluoride are measured.     

Nanosecond pulsed power generator for a voltage amplitude up to 300 kV and a repetition rate up to 16 Hz for fine disintegration of quartz

A generator of high-power high-voltage nanosecond pulses is intended for electrical discharge disintegration of mineral quartz and other nonconducting minerals. It includes a 320 kV Marx pulsed voltage generator, a high-voltage glycerin-insulated coaxial peaking capacitor, and an output gas spark switch followed by a load, an electric discharge disintegration chamber. The main parameters of the generator are as follows: a voltage pulse amplitude of up to 300 kV, an output impedance of ≈10 Ω, a discharge current amplitude of up to 25 kA for a half-period of 80–90 ns, and a pulse repetition rate of up to 16 Hz.     

Generation of X-ray radiation with a high pulse repetition rate by means of a volume discharge in an open gas diode

The subject of study is ultrashort avalanche-produced electron pulses generated in air under atmospheric pressure. The current amplitude of the pulses behind 45-μm-thick AlBe foil exceeds 100 A, and their FWHM is ≈0.2 ns. The conditions of generation of ultrashort pulses persist at repetition rates as high as 1.5 kHz. A volume discharge initiated in an open coaxial-electrode gas diode by high-voltage nanosecond pulses generates hard (> 60 keV) radiation.     

Structural and phase transformations of sulfide mineral surfaces irradiated by nanosecond electromagnetic pulses

The effect of high-voltage nanosecond electromagnetic pulses on the phase composition of chalcopyrite and sphalerite surfaces is investigated by IR-Fourier spectroscopy, XPS, and UVS. Electromagnetic pulse treatment results in the formation and accumulation of copper and/or iron sulphates Me _x (SO₄) _y in superficial chalcopyrite layers, zinc sulphate ZnSO₃, and carbonate ZnCO₃ on sphalerite surfaces, changing their electrochemical and physicochemical properties; i.e., a rise in electrode potentials creates favorable conditions for anionic collector sorption and promotes sulfide flotation activity.     

Changes in the surface phase composition of sulfide minerals upon irradiation by high-power nanosecond pulses

The effect of high-power (high-voltage) nanosecond pulses on the phase composition and chemical state of atoms of surface layers of sulfide minerals with different semiconductor properties (galenite, molybdenite, and sphalerite) is investigated by means of XPES. Common patterns and characteristic features of the structural phase transformations of sulfide surfaces under the pulsed energetic effect are the formation and growth of a surface layer by the nonstoichiometric sulfur-enriched sulfide phase and Zn and Mo oxides and hydroxides; the staged character of the transformation of sulfur atoms in the composition of galenite and sphalerite surface layers; and the stability of the chemical state of sulfur in the molybdenite composition and lead atoms in the galenite composition.     

Development of high-voltage nanosecond discharge in combustible mixtures

The discharge development inmethane- and hydrogen-oxygenmixtures under repeated high-voltage nanosecond pulses is studied. It is shown that the fraction of the energy deposited in the methane-oxygen-mixture discharge and the maximum discharge current pass through a minimum with increasing number of pulses, and the plasma decay rate, on the contrary, reaches a maximum. The observed features are explained by partial fuel oxidation with the result that intermediate components are accumulated in the combustiblemixture, which result in rapid electron loss and decay plasma enhancement.     

Energy concentration in electric discharges between particles of semiconducting sulfide minerals under the action of high-power nanosecond pulses

A model for development of electric discharges between particles of sulfide minerals (pyrite) under the action of high-voltage nanosecond pulses is proposed. It is shown that through discharges in a layer of pyrite particles lead to energy concentration in small contact regions between particles; the concentrated energy is sufficiently high for local decomposition (disintegration) of mineral complexes.     

Compact 1000 pps high-voltage nanosecond pulse generator

A compact high-voltage nanosecond generator is described with pulse repetition rate of up to 1000 pps. The generator includes a 30-Ω coaxial forming line charged by a built-in Tesla transformer with high coupling coefficient, and a high voltage (N₂) gas gap switch with gas circulating between the electrodes. The maximum forming line charge voltage is 450 kV, the pulse duration is ~4 ns, and its amplitude for a matched load is up to 200 kV. The generator has been applied to create powerful sources of ultrawide-band electromagnetic radiation and nanosecond microwave pulses     

Formation of micro- and nanophases on sulfide mineral surfaces under the effect of nanosecond electromagnetic pulses

The gas outflow from nanosecond breakdown channels of sulfide minerals under high-power electromagnetic pulses is considered with regard to iron and sulfur vapor condensation. New experimental data on the structural and chemical transformations of sulfide mineral surfaces under nanosecond pulse action are reported.     

Electromagnetic radiation of a nanosecond discharge in an open gas-filled diode

The properties of the discharge in and radiation from an open gas-filled diode to which high-voltage nanosecond pulses are applied from the RADAN-220 generator are studied. Electromagnetic radiation in the X-ray, UV, visible, and near-IR ranges of the spectrum, as well as high-power subnanosecond (0.5-to 0.7-ns-long) pulses of ultra-wide-band (UWB) electromagnetic radiation, are recorded when a diffuse discharge is initiated in atmospheric pressure air. For the coaxial cathode and anode, the open gas diode emits radially polarized UWB pulses, whereas for the cathode in the form of a segment, the UWB radiation is linearly polarized. The effective potential for both designs of the diode is ER = 6 kV. It is shown that the plasma in the discharge gap serves as a source of soft X rays and the metallic anode generates hard X rays.     

Cooperative formation of dust structures in plasma

The formation and destruction of ordered dust structures in glow discharges are investigated experimentally. The initial construction phase of an ordered structure is related to the construction of its cooperative field and is determined by the number of particles and by the existence of crystallization centers. After the structure has been constructed, it influences the local plasma properties and the discharge current-voltage characteristics. The recovery of the structure after weak exposure takes place at local equilibrium, while, after intense exposure to high-voltage nanosecond pulses, it is determined by the fluctuation level and the degree of chaotization in the system.     

多路高电压纳秒矩形波脉冲发生器的研制

为满足脉冲功率实验中对多路高电压纳秒矩形波激励的需求,研制了一台21路高电压纳秒矩形波发生器。此发生器由一个单路高电压纳秒矩形波脉冲发生器和一个21路分路器组成。其中单路高电压纳秒矩形波脉冲发生器可输出幅值约1.07kV、半高宽约10ns、上升沿约1.45ns的矩形波脉冲。利用21路分路器可将该矩形波脉冲分为21路矩形波脉冲,测得每路脉冲幅值可达51V,半高宽约为10ns,上升沿约为2.25ns。     

Generation of nanosecond pulses in a barrier-discharge XeBr excimer lamp

The subject of investigation is the coaxial two-barrier short-pulse excimer lamp based on XeBr* molecules (λ = 282 nm). When the working mixture (Xe: Br₂ = 70: 1) is excited by a high-voltage pulsed nanosecond discharge at a pressure of 1 atm, the peak power of the generated radiation is on the order of 100 kW at an FWHM of 4.5 ns. If the gap between the barriers is small, a train of pulses with an FWHM of 20 ns and a repetition rate of 200 kHz may be obtained.     

Experimental study and computer simulations of the implantation of laser plasma ions in pulsed electric fields

Results are presented from experimental studies of pulsed plasma flows generated by nanosecond laser pulses with an intensity of 7 × 10⁸ W/cm² from a solid-state target in a strong electric field. The current pulses through the laser target and the depth distributions of the iron ions implanted in a silicon substrate to which a negative high-voltage pulse was applied are measured. The physical processes occurring in laser plasma with an initial iron ion density of 6 × 10¹⁰ cm⁻³ are simulated numerically by the particle-in-cell method for different delay times and different shapes of the accelerating high-voltage pulse. The model developed allows one to calculate the ion flows onto the processed substrate, the electron flows onto the target, and the energy spectra of the implanted ions. The results from computer simulations are found to be in good agreement the experimental data.     

X-ray radiation due to nanosecond volume discharges in air under atmospheric pressure

The formation of nanosecond discharges in atmospheric-pressure air versus the applied pulse polarity and discharge gap geometry is studied. It is shown that the polarity of high-voltage nanosecond pulses and the electrode configuration have a minor effect on the volume discharges under a variety of experimental conditions. When the spacing between needle-like electrodes is large, the discharge is asymmetric and its glow is weakly dependent on the sign of the potential applied to the electrode. Negative voltage pulses applied to the potential electrode generate X-ray radiation from both the surface and volume. For a subnanosecond rise time of the voltage pulse and diffusion character of the discharge, the X-ray radiation comes from the brightly glowing region of a corona discharge. The average values of the fast electron velocity and energy in nitrogen are calculated. At field strengths E/p < 170 kV/cm atm, the average velocity of a fast electron bunch is constant because of central collisions. At field strengths E/p > 170 kV/cm atm, fast electrons run away. Central collisions are the reason for X-ray radiation from the volume.     

Electron flux spatial distribution in an ultrashort avalanche electron beam generated at atmospheric air pressure

The results of experimental study on generation of ultrashort avalanche electron beams (UAEB) in gas-filled diodes are considered. The spatial distribution of the flux of runaway electrons and X-rays generated in the gas diode fed by nanosecond high-voltage pulses was studied. It was shown that the UAEB in the gas-filled diode (at an air pressure of 1 atm) with sharply nonuniform electric field is generated from the interelectrode region into a solid angle exceeding 2π sr. Narrowing of the cathode-anode gap results in a decrease in the current amplitude of the beam generated to side walls of the gas diode and an increase in the beam current pulse duration in both axial and radial directions. Current pulses of the beam initiated from the side surface of the tubular cathode were detected.