Shock Waves In Plasma Research Articles

On the effects of different regimes of plasma pulses affecting the material due to their succession

The tungsten (>99.97% W) samples were irradiated on plasma focus device (PF-12), with deuterium (D) as a working gas, in Tallinn University in Estonia. Two of the samples serve as references, being irradiated in only one regime (either in harsh regime with heat flux factor ∼1000 MW s1/2 m2 for plasma and ∼1.5•105 MW s1/2 m2 for fast ions, or in the mild regime with heat flux factor ∼40–45 MW s1/2 m2 for plasma and ∼2000 MW s1/2 m2 for fast ions). Three of the samples received 27 pulses combining the two aforementioned regimes. The combined effects are obtained by using two different plasma flux values and also by varying the timing when the harsh regime is implemented during the irradiation cycle of each sample. The research is conducted by analyzing the SEM images of the damaged surfaces, measuring the electrical conductivity of the material in the bulk, studying the SEM images and micro-hardness of sample's cross-sections. This will enable to draw conclusions on the range of damages due to the varied succession of used regimes. The results are then combined to estimate the applicability of conductivity measurements instead of using destructive invasive measuring methods (i.e., measurement of micro-hardness and SEM imaging of cross sections).The aims of our research is to shed some light on (1) whether and how the succession of different series of irradiations with varying power flux densities affects the formation of damages on and within the samples and (2) estimating the three-dimensional damages that are created within the bulk of material due to high-temperature plasma and ion shockwaves. Our study indicates that the damage in bulk is related to the timing of harsh regime plasma pulses. The use of measurements of conductivity enables to estimate the future development of the damages in bulk of the material.

Dynamics and density distribution of laser-produced Al plasmas using optical interferometry and optical emission spectroscopy

The dynamic evolution and density distribution of laser-produced plasmas (LPP) of Al in air at atmospheric pressure were investigated using optical interferometry and optical emission spectroscopy, respectively. Interferograms were obtained in Mach–Zehnder interferometry with a laser pulse energy of 35 mJ and delay times from 200 ns to 6.9 µs. From the shift in interference fringes within this time interval and Taylor–Sedow theory, the expansion profiles of the shock wave were found to be hemispherical and approached planar propagation. The expansion and evolution of the plasma plume were also studied by exploiting the phase shift and refractive index obtained from the interferograms using the fast Fourier transformation and Abel transformation. Three-dimensional spatial expansion profiles of the plasma plume and shock wave were presented. In addition, two-dimensional electron density distributions of the Al plasmas were obtained from the spatial dependence of the refractive index of plasma, and compared with the results of optical emission spectroscopy. The results from the two diagnostic methods and their advantages and disadvantages are discussed. This work exploits two diagnostic methods to study the dynamic evolution and the density distribution of the LPP in air at atmospheric pressure and provides an important base reference for developing LPP applications in many fields.

Surface integrity of 2A70 aluminum alloy processed by laser-induced peening and cavitation bubbles

This paper presents a novel compound strengthening method based on laser-induced peening and cavitation peening (LIPCP). 2A70 aluminum alloy was strengthened by plasma shock wave and cavitation bubble collapse shock wave. The dynamic characteristic of cavitation bubble was captured by using a high-speed camera, and the strengthening mechanism of LIPCP was detailed elaborated. The peening depth was measured by an ultra-depth-of-field microscope and increases with increasing laser energies. But the surface roughness decreases with an increase in laser energies. The surface, after the compound strengthening, improved considerably with the laser energy and impact times, and has higher compressive residual stress. However, the compressive residual stress reaches a saturation value in the first 5 impacts due to the formation of a hardened layer on the material surface. In addition, ultrasonic cavitation erosion experiments were performed in 3.5% NaCl solution at room temperature. The results reveal that there are four typical cavitation erosion periods during the cavitation erosion process, and the mass loss rate of the treated specimen is relatively lower than that of the untreated specimen. The microscopic morphology analysis shows that there are large smooth areas on the LIPCP treated surface after ultrasonic cavitation erosion, which indicates that the fatigue life and cavitation resistance of 2A70 alloy aluminum has been greatly improved. The LIPCP provides a promising method to strengthen the hydraulic machinery beneath the water.

Two‐dimensional magnetosonic shock wave propagation in dense electron–positron–ion plasmas

Two‐dimensional (2D) magnetosonic wave propagation in magnetized quantum dissipative plasmas is studied. The plasma system is comprised of inertial ions, inertia‐less electrons, and positrons. The multi‐fluid quantum hydrodynamic model is used, in which quantum statistical and quantum tunnelling effects of electrons and positrons are included. Reductive perturbation analysis is performed to derive the Zabolotskaya–Khokhlov equation for the 2D propagation of a magnetosonic shock wave in a magnetized qauntum plasma. The effects of varying the different plasma parameters such as positron density and magnetic field intensity on the propagation characteristics of magnetosonic shock waves are discussed with non‐relativistic degenerate plasma parameters in astrophysical plasma situations.

Study of obliquely propagating electron acoustic shock waves with non-extensive electron population

Obliquely propagating electron acoustic shock waves in magnetized plasma composed of stationary ions, cold and non-extensive hot electrons are investigated by deriving Korteweg–de Vries Burgers (KdVB) equation. The tangent hyperbolic method is used to solve the KdVB equation in dissipative medium. The dissipation effect is introduced in the model by means of kinematic viscosity term. The analytical calculations of the KdVB equation shows that the structures (amplitude, velocity and width) of the shock waves are modified significantly with kinematic viscosity (η0), obliqueness (kz) and magnetic field (ωc). Since plasmas are ubiquitously permeated with magnetic field, it is pertinent to explore the characteristics of KdVB equation in a magnetized plasmas.

Enhancement of carbon detection sensitivity in laser induced breakdown spectroscopy with low pressure ambient helium gas

Carbon detection is usually difficult to carry out with high sensitivity and minimally destructive effect. While the conventional laser induced breakdown spectroscopy (LIBS) method operated with atmospheric ambient air is well known as a powerful and versatile analytical tool, it suffers nevertheless from the low sensitivity of C detection when measured in both atmospheric and low pressure ambient air with the more adverse effect found in the former case. This was shown to have its origin in the serious time mismatching effect between the formation of the shock wave plasma by the ablated major host elements and the premature fast passage of the much lighter ablated C atom. However, this study shows the result of high sensitivity C analysis of stone samples using LIBS technique with relatively low laser pulse energy of 60 mJ and low pressure He ambient gas without showing visible surface damage. The helium gas provides the additional delayed excitation by the He metastable excited states through the Penning-like ionization process. The C emission intensities measured from the jasper and black stone in 2.6 kPa He ambient gas are in general significantly higher than those measured in 0.5 kPa ambient air. The enhancement is shown to increase reaching an 8 fold enhancement with increased laser energy up to 60 mJ before undesirable surface damage is created. A further measurement of C emission using pelletized KBr mixtures with various CaCO3 concentrations reveals a straight calibration line of rather large slope with extrapolated zero intercept and estimated detection limit of around 0.6 ppm, demonstrating its potential application for highly sensitive quantitative analysis of C with minimal destructive effect.

Peculiarities of the charged particles distribution near the front of a shock wave in a glow discharge plasma

The charged particles distribution in a glow discharge plasma near the front of shock wave moving perpendicularly to the discharge axis has been investigated using a double electrical probe. It has been shown that the interaction of the shock wave with the glow-discharge plasma is accompanied by a decrease of charged particles density before the shock wave arrival to the measurement point. This decrease occurs simultaneously through the entire plasma volume. The short-term increase of charged particles density has been revealed. Its appearance caused by interaction of a shock wave with the cathode layer of a glow discharge. These peculiarities of charged particles distribution compared with the case when shock wave propagates through decaying plasma. A significant difference between the distributions of the charged particles in these two cases was revealed.

2-D Numerical Investigation of the Formation of Z-Pinch-Driven Dynamic Hohlraum at 8-MA Current Level

The newly developed code MULTI2D-Z is applied to simulate the formation process of a dynamic hohlraum driven by tungsten wire-array Z-pinch at 8-MA current level. In the initial phase, the foam is expanding due to the radiation heating from the imploding wire-array plasma. At the same time, this causes a compression-wave spreading inward in the foam, and in turn a challenge for the safety of capsule embedded in the center of the foam in the inertial confinement fusion ignition experiment. There is instability development during the collision of the expanding foam plasma and the imploding wire-array plasma. However, fortunately, this instability was then spontaneously restrained due to the subsequent snow-plow implosion. The formed wall-like high-Z plasma (shock wave), in which the radiation mean free path is about 10 $\mu \text{m}$ , compresses the foam, and plays a well role in trapping the radiation in the foam. When the foam has been compressed a little and the high-Z plasma temperature decreases, the dynamic hohlraum begins to form. While the thermal radiation wave in the foam is spreading toward the center axis, the radiation temperature profile becomes comparatively uniform, and almost equates to the plasma (matter) temperature except at the place of the shock wave. The radiation temperature in the hohlraum is above 100 eV. The simulated results also suggested that the radiation energy loss to the electrodes would be one of the main reasons for the nonuniformity in the radiation field and implosion instability development during hohlraum formation.

Obliquely Propagating Electron Acoustic Shock Waves in Magnetized Plasma

Obliquely propagating electron acoustic shock waves in plasma with stationary ions, cold and superthermal hot electrons are investigated in magnetized plasma. Employing reductive perturbation method, Korteweg-de Vries-Burgers equation (KdVB) is derived in the small amplitude approximation limit. The analytical and numerical calculations of the KdVB equation show the variation of shock waves structure (amplitude, velocity, and width) with different plasma parameters. Particle density (α), superthermal parameter (κ), electron temperature ratio (𝜃), kinetic viscosity (η0), obliqueness (kz), and strength of magnetic field (ωc) significantly modify the properties of the shock waves structures. The present investigation is useful to understand dissipative structures observed in space or laboratory plasma where multielectrons population with superthermal electrons are prevalent.

Generation of dispersive shock waves in nonextensive plasmas

In this research we use a generalized hydrodynamic model to numerically investigate the quasi-neutral expansion and compression of an electron–ion plasma with nonextensive electron velocity distribution into or from vacuum. We study the effects of kinematic viscosity and electron–ion collisions on the expansion profile and compare our results to the numerical solutions of the standard Korteweg – de Vries (KdV) equation. It is found that the quasi-neutrality assumption in the hydrodynamic approach in the absence of viscosity and collisions, which leads to elimination of Poisson’s equation, sets the weak dispersion limit and becomes equivalent to the standard weakly dispersive KdV model. In the weak dispersion limit our model, as well as the KdV with small dispersion effect, predicts that a pulse-like initial profile evolves into solitary wave train. We further show that in a plasma expansion different shock profiles, such as purely dispersive, diffusive–dispersive, and dissipative ones, with significantly different characters may form. Finally, the effect of electron nonextensivity on oscillatory shock waves shows that the expansion profile is affected by changes of q-parameter. Our numerical solution is in qualitative agreement with some distinguished experiments showing the possibility of dispersive shock wave formation in rarefied plasma during an expansion into vacuum.

Effect of ion drift on shock waves in an un-magnetized multi-ion plasma

We investigate the effect of the drift velocity of lighter ions on shock waves in an unmagnetized multi-component plasma. Solar origin hot electrons and lighter ions, positively and negatively charged heavier ions and cometary origin colder electrons form the multicomponent plasma. Using the reductive perturbation technique, we have derived the KdVB (Korteweg-deVries-Burgers) equation and its shock wave solution is plotted for different plasma parameters relevant to comet Halley. We find that the strength of the shock profile decreases with increasing drift velocities of the lighter ions and kappa indices of the two components of electrons. On the other hand, the amplitude of the shock increases with increasing kinematic viscosities and densities of the lighter ions. Also, different coefficients of the KdVB equation are strongly affected by the drift velocities of the lighter ions.

Investigation of cylindrical shock waves in dusty plasma

Electronegative dusty plasma composed of Boltzmann electrons, Boltzmann negative ions, inertial positive ions and charge fluctuating dust has been considered. The fractional modified Burgers’ (FMB) equation, which is derived using Euler–Lagrange variational technique, is analytically obtained and solved for studying the cylindrical geometry effect on the propagation of the dust ion acoustic shock wave. The Laplace homotopy perturbation method, the so-called LHPM is applied to solve the FMB equation. The effect of the fractional parameter, positive ion number density at equilibrium, the number of equilibrium electrons residing on the dust grain surface and shock velocity on the behavior of the shock waves in the dusty plasma has been investigated.

3D Burgers Equation in Relativistic Plasma in the Presence of Electron and Negative Ion Trapping: Evolution of Shock Wave

The characteristics of shock waves in a relativistic plasma in the presence of nonisothermal electrons and nonisothermal negative ions is investigated by deriving the evolution equation in terms of a modified 3D Burgers equation, or trapped 3D Burgers equation. The solution of this equation is examined analytically to study the salient characteristics of shock waves in such plasma. The nonlinear coefficient is found to have the lowest (highest) value when the negative ions move toward thermal equilibrium with a dip-shaped electron distribution (when both electrons and negative ions follow a dip-shaped distribution) for a particular value of relativistic factor, and it remains in an intermediate state when both electrons and negative ions follow a flat-topped distribution. On the other hand, the dissipative coefficient is found to decrease (increase) with increasing relativistic parameter (viscous parameter). A profound effect of the trapped state of both electrons and negative ions and the temperature ratio between positive ions and electrons (negative ions and electrons) on the structure of the shock wave is also seen. However, it has been noticed that the trapped parameter of electrons has a dominating control over the shock potential profile than the trapped parameter of negative ions.

On the nonlinear solitary and shock waves in Maxwellian multicomponent space plasma

Our objective is to study the nonlinear wave phenomena in a multicomponent plasma with Maxwellian electrons and ions. The main reason for this consideration is to exhibit the effects of dust charge fluctuations in plasma acoustic modes. Different aspects of nonlinear dynamics have been studied through the Korteweg-deVries (K-dV) equation (solitons) and the Burgers equation (shocks) derived by the reductive perturbation technique. A special method, known as the (G′/G) method, has been used for a solution. It predicts the different coherent features of various nonlinear waves successfully, and finally, their importance has been recognized in space plasmas. Evolutions have been shown with the input of appropriate typical plasma parameters to support our observations in space plasmas. All conclusions are in good agreement with the actual occurrences and could be of interest in furthering investigations in experiments and satellite observations in spaces. An important aspect of this exercise is a comparative study of K-dV and Burgers solutions in different plasma spaces.

Effect of non-thermality of electron and negative ion on the polarity of shock waves in a relativistic plasma

Considering the effect of non-thermality of electrons and negative ions, the evolution of shock waves and their characteristics in a relativistic plasma is investigated by deriving a three-dimensional Burgers' (3D-Burgers') equation. Based on the stationary solution of the 3D-Burgers' equation, the nature of propagation of shock waves for different suitable physically admissible ranges of plasma parameters, is carried out. Both compressive and rarefactive shock waves are found to propagate in such plasma under different combinations of non-thermal plasma parameters. The critical values of non-thermal electron and negative ion parameters, normalized electron, and negative ion density under which the non-linear co-efficient vanishes is sought. The nature of propagation of shock waves, below, above, and at the critical parameters is carried out. The non-thermal population of negative ions and electrons as well as normalized electron and negative ion density plays a pivotal role in controlling the polarity of the shock wave propagation. Compressive and rarefactive shock is found to propagate simultaneously with the non-thermal population of negative ions for different chosen values of normalized negative ion density at the critical value of normalized electron density.

Regional effects and mechanisms of nanoparticle removal from Si substrate by laser plasma shock waves

We use laser-induced plasma shock waves to remove Al nanoparticles from a smooth silicon substrate. Our experimental results show that the removal mechanism varies for different substrate regions. We examine the factors influencing particle removal by evaluating the shock-wave spatial distribution and the removal mechanisms. Further, we evaluate the influence of the gap between the laser focus and substrate on the removal results. The effects of the laser focus and substrate particle sizes are also investigated, and the optimum removal conditions are obtained. Our study can aid in better understanding the mechanisms of particle removal from surfaces.

Shock wave plasma generation in low pressure ambient gas from powder sample using subtarget supported micro mesh as a sample holder and its potential applications for sensitive analysis of powder samples

We present in this report the results of experimental study on the spectrochemical analysis of powder samples using subtarget supported micro mesh (SSMM) sample holder in low pressure ambient gases. The study is substantiated by establishing the analyte excitation mechanism with the evidence of shock wave plasma generation and the high temperature induced subsequently required for the thermal excitation and emission of the ablated atoms. The application of SSMM sample holder using Cu subtarget and stainless steel micro mesh to a number of powder samples in low pressure ambient gases are shown to produce generally sharp emission lines with low background, without suffering from intensity reduction and matrix effect commonly found in the use of pelletized powder samples. The same excellent spectral quality is demonstrated by its application to the analysis of rice samples which is the major staple diets in a large number of countries. In particular the analysis of Zn in rice is shown to exhibit a linear calibration line with extrapolated zero intercept and a detection limit of <0.87 μg/g which is promising for quantitative analysis.

Electron and ion acceleration by relativistic shocks: particle-in-cell simulations

The problem of particle acceleration by collisionless astrophysical shocks is of fundamental importance for the cosmic ray origin problem and for the high energy astrophysics as a whole. Fast magnetohydrodynamical shocks produced by relativistic jets are considered as very likely sites of cosmic ray acceleration. While cosmic ray acceleration by both non-relativistic and ultra relativistic shocks was studied in some details, the shocks of moderate Lorentz factors have attracted much less attention so far, while they are important for modeling gamma-ray burst afterglows and a number of other interesting objects. In this paper we present simulations of relativistic shock waves in electron-proton plasmas obtained with an implicit particle-in-cell code for the initial study the particle injection efficiencies.

On the formation and properties of fluid shocks and collisionless shock waves in astrophysical plasmas

When two plasmas collide, their interaction can be mediated by collisionless plasma instabilities or binary collisions between particles of each shell. By comparing the maximum growth rate of the collisionless instabilities with the collision frequency between particles of the shells, we determine the critical density separating the collisionless formation from the collisional formation of the resulting shock waves. This critical density is also the density beyond which the shock downstream is field free, as plasma instabilities do not have time to develop electromagnetic patterns. We further determine the conditions on the shells initial density and velocity for the downstream to be collisional. If these quantities fulfil the determined conditions, the collisionality of the downstream also prevents the shock from accelerating particles or generating strong magnetic fields. We compare the speed of sound with the relative speed of collision between the two shells, thus determining the portion of the parameter space where strong shock formation is possible for both classical and degenerate plasmas. Finally, we discuss the observational consequences in several astrophysical settings.

Influence rules of ground-based laser active removing centimeter-sized orbital debris in LEO

The aim of this article is to describe the influence rules of ground-based laser irradiating centimeter-sized orbital debris in low earth orbits (LEO) by numerical simulations and experiments. A dynamic response model of ground-based laser irradiating centimeter-scale orbital debris in LEO was established by analyzing the influences of atmospheric turbulence and beam jitter. The spatial distribution rules of far field spot diameter and far field power density with transmission distance were investigated, the effects of divergence angle to integral spot were analyzed, and the relation of divergence angles and increment of far field spot diameters were also addressed within the turbulent atmosphere. Further, the spatial and temporal distribution rules of velocity and pressure in aluminum target and plasma shock wave were described, and the influence rules of impulse coupling coefficients with power density were also discussed. As a result, the effects of eccentricity and perigee altitude with the number of laser pulses and initial true anomaly were obtained to evaluate removing ability. Hence, it has very important significance for selecting efficient removal schemes to clean centimeter-sized orbital debris in LEO.