The results of the experimental and numerical study of a high-voltage nanosecond discharge developing through a shock wave in air and combustible mixtures were presented for various neutral density ...jumps across the wave. The discharge uniformity was investigated using ICCD camera images in a shock tube. The results demonstrated that the discharge plasma became more uniform when the ionization wave moved from a high-density region to a low-density region. The radiation intensity emitted by the plasma in the low-density region was higher than that emitted by the plasma in the high-density plasma. The results of a zero-dimensional simulation in the case of quasi-uniform plasma agree well with the measured ratios of the intensities radiated by the plasmas before and after the shock front. A two-dimensional simulation of the development of a steamer intersecting the shock wave showed that the streamer characteristics change drastically during the transition from the high-density region to the low-density region. Streamer penetration into the low-density region was accompanied by the formation of primary and secondary ionization waves.
The kinetics of ignition in CnH2n + 2:O2:Ar mixtures for n=2 to 5 has been studied experimentally and numerically after a high-voltage nanosecond discharge. The ignition delay time behind a reflected ...shock wave was measured with and without the discharge. It was shown that the initiation of the discharge with a specific deposited energy of 10 -30 mJ/cm3 leads to an order of magnitude decrease in the ignition delay time. Discharge processes and following chain chemical reactions with energy release were simulated. The generation of atoms, radicals and excited and charged particles was numerically simulated using the measured time-resolved discharge current and electric field in the discharge phase. The calculated densities of the active particles were used as input data to simulate plasma-assisted ignition. The sensitivity of the results to variation in electron cross sections, reaction rates and radical composition was investigated. Good agreement was obtained between the calculated ignition delay times and the experimental data. The analysis of the simulation results showed that the effect of nonequilibrium plasma on the ignition delay is associated with faster development of chain reactions, due to atoms and radicals produced by the electron impact dissociation of molecules in the discharge phase. Finally, we studied the role of various hydrocarbon radicals in the plasma-assisted ignition of the mixtures under consideration.
The kinetics of ignition in lean and stoichiometric C2H5OH:O2:Ar mixtures by a high-voltage nanosecond discharge are studied experimentally and numerically for gas temperatures above self-ignition ...threshold. Autoignition delay time and ignition delay after a high-voltage nanosecond impulse discharge are measured using reflected shock-wave technique. It is shown that the additional excitation by the discharge plasma leads to an order of magnitude decrease in ignition delay. Discharge processes are simulated on the basis of the measured time–resolved discharge characteristics. The densities of atoms, radicals and excited and charged particles produced in the discharge phase are calculated and used as initial conditions for chemical modeling. Calculated ignition delay times agree well with measurements with and without the discharge plasma. Calculations show that the effect of the discharge plasma on ignition of the ethanol-containing mixtures is primarily associated with active species production in the discharge phase; the role of fast gas heating during the discharge and in its afterglow is relatively small. A method is suggested to compare the effect of nonequilibrium pulse discharge plasma on ignition in different fuel–air and fuel-oxygen mixtures above self-ignition temperatures. It is shown that this effect is more profound at low gas temperatures when the thermal production of initial radicals is not efficient. Due to O2 dissociation in the discharge phase, the influence of nonequilibrium discharge plasma on ignition is more pronounced for fuels with high activation energy of thermal dissociation (like H2 and CH4). The role of N2 in favoring plasma-assisted ignition owing to additional O2 and fuel dissociation is demonstrated.
Abstract
The results of experiments on the study of plasma compression of nested wire arrays of mixed composition and the generation of powerful pulses of soft x-ray radiation (SXR), carried out on a ...pulse power facility Angara-5-1 at a current level of up to 3 MA, are presented. Based on the latest experimental data on the intensity of plasma formation of various substances
m
˙
(in
μ
g(cm
2
ns)
−1
) (Mitrofanov
et al
2020
Plasma Phys. Rep.
46
1150–80) and on the features of the dynamics of plasma compression in nested arrays (Mitrofanov
et al
2018
Plasma Phys. Rep.
44
203–35), a nested wire array design has been developed which makes it possible to obtain a high peak SXR power in comparison with the known designs of single and nested tungsten wire arrays. During the implosion of nested arrays of mixed composition, consisting of plastic fibers and tungsten wires, shorter and more powerful SXR pulses were obtained with a maximum peak power
P
SXR
max
∼ 10 TW with a full width at half maximum (FWHM) duration of ∼5 ns compared to the parameters of SXR pulses upon compression of single tungsten arrays:
P
SXR
max
∼ 5 TW and FWHM ∼ 10 ns. Thus, under the conditions of our experiments, we have shown the possibility of a twofold increase in the peak SXR power during compression of nested arrays by optimizing their design.
Abstract
Determining the nature of dark matter (DM) is one of the most important challenges of modern experimental physics. This article overviews the major arguments confirming the existence of DM, ...gives the latest classifications of DM particles, identifies possible candidates for their role, and discusses the most significant DM particle search experiments conducted and under development. The article mainly aims to give an idea of diverse experimental methods of and approaches to registering DM particles, as well as of the currently available results of the search for them, which open new prospects in DM studies and contribute to solving topical problems in New Physics.
Spectral properties of the high-temperature plasma obtained by exposing a nickel layer to a source of high-power X-ray radiation (a power of 6–10 TW with a duration of 7–10 ns) based on a Z-pinch, ...formed during implosion of tungsten multi-wire arrays at the Angara-5-1 facility, are studied. In this case, the Z‑pinch radiation heats the target and turns it into the hot plasma, and the same radiation probes the target plasma to determine the spectral dependence of the transmission of this plasma. An original scheme is proposed for measuring the incident, transmitted and self-emission of a target simultaneously in one experiment in the frame mode using a grazing incidence diffraction spectrograph. Using laser shadow imaging, experimental data are obtained on the velocity of the plasma expansion on the irradiated and back sides of the target, which reached 100 km/s. Targets made of thin Ni layers deposited on a mylar film are studied. An irradiation-induced multiple increase in the transmission of the target plasma in the EUV range is observed compared to the transmittance of the target in the cold state. The dependence of the absorption spectrum of the plasma and the accompanying self-radiation of the target on the power and shape of the heating pulse is studied. The measurement results are compared with numerical calculations performed using the RALEF-2D two-dimensional radiation code, which has been repeatedly used previously to simulate similar experiments. The shape of the spectral dependence of the transmission in the experiment and calculation is similar in the range of ∼30–200 Å, but the model plasma transmission (∼0.8–0.9) is higher than that obtained using a spectrograph and X-ray multi-frame photography (∼0.5–0.6).
We study experimentally and numerically the kinetics of ignition in lean and stoichiometric C2H2 : O2 : Ar mixtures after a high-voltage nanosecond discharge. The ignition delay time is measured ...behind a reflected shock wave with and without the discharge using detection of CH radiation. Generation of the discharge plasma is shown to lead to a decrease in ignition delay time. Discharge processes followed by chain chemical reactions with energy release are simulated during ignition in the C2H2 : O2 : Ar mixtures. The generation of atoms, radicals and excited and charged particles in the discharge phase is numerically simulated. The calculations are based on the measured time-resolved discharge current and electric field. The calculated densities of the active particles produced in the discharge on a nanosecond time scale are employed as input data to simulate plasma-assisted ignition on a microsecond scale. The calculated ignition delay times are compared with the experimental data. It is shown that the effect of the discharge plasma on ignition of the acetylene-containing mixtures is associated with active species production in the discharge phase rather than with gas heating during the discharge and in its afterglow. A sensitivity analysis is made to determine limiting reactions in acetylene autoignition and ignition after the discharge under the conditions studied.
A new study of a historical object on the territory of the Russian Federation, the Holy Trinity Danilov Monastery, implemented by the muon radiography is presented. The method is based on the ...registration of changes in the cosmic muon fluxes during their passage through the object under study. Nuclear photoemulsions with unique spatial and angular resolution having the widest range of applications in experimental nuclear physics were used as experimental equipment. The experiment demonstrates a high efficiency of the method in the search for hidden objects, the presence of which on the territory of the monastery is confirmed by the results obtained.
The results of research on the creation of a powerful source of soft X-ray radiation (SXR,
h
ν > 100 eV) based on the Z-pinch of compact nested arrays are presented. One of the applications of such ...an SXR source can be radiation ablation of targets made of various substances in experiments on high-energy density physics and extreme states of matter, which are currently being actively carried out worldwide. Experiments are carried out on plasma implosion of combined nested arrays with different ratios of array radii at a discharge current level of up to 3.5 MA at the pulse power facility Angara-5-1. The outer array consisted of fibers of a substance with a low atomic number (polypropylene) and the inner array consisted of a substance with a high atomic number (tungsten). It is shown that in the case of nested arrays of this design, it is possible to obtain a significant (~1.4 times) increase in the peak SXR power compared to single W arrays with the same parameters as the W array in the inner array. At the same time, spectral data obtained using a “flat field” grazing incidence spectrograph demonstrate a significant decrease in the fraction of tungsten ions in the trailing plasma around the pinch of nested arrays. By optimizing the linear mass of the outer array and its radius, powerful and short SXR pulses with amplitude of ~10 TW, energy of ~130 kJ and duration of ~4–5 ns are obtained. This made it possible to increase the incident power density and fluence on the target up to 1.55 TW/cm
2
and 17 kJ/cm
2
, respectively, in experiments on extreme states of matter currently being carried out at the facility.
At the Angara-5-1 facility investigation was carried out which studied the interaction of plasma flows and the magnetic field. They are created by the current implosion of cylindrical nested wire ...arrays, the inner and outer array of which are composed from thin wires or dielectric fibers. It has been shown experimentally that at the plasma formation stage it is possible to realize various modes of interaction between plasma flows and the magnetic field of the discharge current inside the nested array. A mechanism is proposed for the interaction of plasma flows of the outer array with the magnetic field and the current-carrying plasma of the inner array. The stability of the plasma compression of the inner array at the final stage of its compression depends on the nature of this interaction. Obtained experimental data on the dynamics of interaction of plasma flows with the magnetic field in the gap between arrays are compared with the results of 2D-simulation of the implosion of nested arrays according to the RMHD MARPLE code. It is experimentally and theoretically confirmed that when a nested array is imploded with certain parameters around the inner array, a plasma quasi-closed shell is formed in the azimuthal direction.
