Plasma Shock Research Articles

Simulation and Experimental Study of Nanosecond Pulse Laser Removal of Epoxy Paint on 6061 Aluminum Alloy Surface

Laser paint removal is a new cleaning technology that mainly removes paint through thermal ablation and mechanical stripping mechanisms. This paper established a thermal-mechanical coupling laser removal model of paint based on the heat conduction equation, Newton’s second law, and Fabbro’s theory. The removal process of epoxy resin paint film on an aluminum alloy surface via a nanosecond pulsed laser was studied using finite element simulations and experimental measurements. The simulation and experimental results show that the nanosecond pulse laser’s primary paint removal mechanism is the mechanical stripping caused by thermal stress and plasma shock. The laser paint removal threshold is 1.4 J/cm2. In addition, due to the different generation times of plasma shock and thermal stress, the mutual superposition of stress waves occurs in the material. This results in a discrepancy between the actual and thermal stress differences. Moreover, the thermal stress difference causes the maximum actual stress difference to fluctuate. The simulation model established in this paper can provide a reference for studying the thermal-mechanical coupling process of laser paint removal.

Endothelial Cell Calcium Influx Mediates Trauma-induced Endothelial Permeability.

We aimed to investigate if ex vivo plasma from injured patients causes endothelial calcium (Ca2+) influx as a mechanism of trauma-induced endothelial permeability. Endothelial permeability after trauma contributes to post-injury organ dysfunction. While the mechanisms remain unclear, emerging evidence suggests intracellular Ca2+ signaling may play a role. Ex vivo plasma from injured patients with "Low Injury/Low Shock" (injury severity score [ISS]<15, base excess [BE])≥-6mEq/L) and "High Injury/High Shock" (ISS≥15, BE<-6mEq/L) were used to treat endothelial cells. Experimental conditions included Ca2+ removal from the extracellular buffer, cyclopiazonic acid pre-treatment to deplete intracellular Ca2+ stores, and GSK2193874 pre-treatment to block the TRPV4 Ca2+ channel. Live cell fluorescence microscopy and ECIS were used to assess cytosolic Ca2+ increases and permeability, respectively. Western blot and live cell actin staining were used to assess myosin light chain (MLC) phosphorylation and actomyosin contraction. Compared to Low Injury/Low Shock plasma, High Injury/High Shock induced greater cytosolic Ca2+ increase. Cytosolic Ca2+ increase, MLC phosphorylation, and actin cytoskeletal contraction were lower without extracellular Ca2+ present. High Injury/High Shock plasma did not induce endothelial permeability without extracellular Ca2+ present. TRPV4 inhibition lowered trauma plasma-induced endothelial Ca2+ influx and permeability. This study illuminates a novel mechanism of post-injury endotheliopathy involving Ca2+ influx via the TRPV4 channel. TRPV4 inhibition mitigates trauma-induced endothelial permeability. Moreover, widespread endothelial Ca2+ influx may contribute to trauma-induced hypocalcemia. This study provides the mechanistic basis for the development of Ca2+-targeted therapies and interventions in the care of severely injured patients.

Prospective evaluation of platelet function and fibrinolysis in 20 dogs with trauma.

To determine platelet function and assess fibrinolysis in dogs following trauma using multiple electrical impedance aggregometry and a modified thromboelastographic (TEG) technique. To determine if the severity of trauma, as assessed by the Animal Trauma Triage (ATT) score and clinicopathological markers of shock, is associated with a greater degree of platelet dysfunction and fibrinolysis. University teaching hospital. Twenty client-owned dogs with trauma (occurring <24h prior to admission and blood sampling) and ATT score of >4 were prospectively recruited. A control group of 10 healthy dogs was included. None. Platelet function was measured using multiple electrode platelet aggregometry (MEPA) utilizing arachidonic acid, ADP, and collagen agonists. Fibrinolysis was assessed in citrated whole blood with the addition of tissue plasminogen activator (tPA; 50U/mL) using kaolin-activated TEG. Conventional statistical analysis was performed to compare coagulation parameters between the groups and assess linear correlations. Median (interquartile range) ATT score was 5 (5-7), and 65% (n=13) of dogs suffered polytrauma. Mean(±SD) time from trauma to blood sampling was 9hours (±6). Median (interquartile range) shock index and plasma lactate concentration were 1.1 (0.7-2.0, n=16) and 2.9mmol/L (0.9-16.0, n=18), respectively. Four dogs did not survive to discharge (20%). There were no differences between the trauma and control group coagulation variables. A moderate negative correlation between ATT score and area under the curve for ADP was found (P=0.043, r2 =-0.496). Preliminary evaluation of platelet function measured by MEPA, and fibrinolysis measured by tPA-modified TEG, is not significantly different in this population of dogs with traumatic injury compared to healthy dogs.

Kinetic Simulations of Nonrelativistic High-mach-number Perpendicular Shocks Propagating in a Turbulent Medium

Strong nonrelativistic shocks are known to accelerate particles up to relativistic energies. However, for diffusive shock acceleration, electrons must have a highly suprathermal energy, implying the need for very efficient preacceleration. Most published studies consider shocks propagating through homogeneous plasma, which is an unrealistic assumption for astrophysical environments. Using 2D3V particle-in-cell simulations, we investigate electron acceleration and heating processes at nonrelativistic high-Mach-number shocks in electron-ion plasma with a turbulent upstream medium. For this purpose, slabs of plasma with compressive turbulence are simulated separately and then inserted into shock simulations, which require matching of the plasma slabs at the interface. Using a novel procedure of matching electromagnetic fields and currents, we perform simulations of perpendicular shocks setting different intensities of density fluctuations (≲10%) in the upstream region. The new simulation technique provides a framework for studying shocks propagating in turbulent media. We explore the impact of the fluctuations on electron heating, the dynamics of upstream electrons, and the driving of plasma instabilities. Our results indicate that while the presence of turbulence enhances variations in the upstream magnetic field, their levels remain too low to significantly influence the behavior of electrons at perpendicular shocks.

Observation of laser ablation of silicon as a function of pulse length at constant fluence via time-resolved x-ray spectroscopy

We investigate the ablation of silicon as a function of laser pulse length at a constant fluence using time-resolved x-ray spectroscopy data obtained from OMEGA EP experiments at the University of Rochester's Laboratory for Laser Energetics. Our targets consisted of three-layer planar structures composed of Si (50 μm), Cu (25 μm), and SiO2 (500 μm) layers. The Si layer was irradiated by a 351-nm laser with varying pulse widths of 250 ps, 500 ps, 1 ns, and 10 ns while maintaining a constant fluence of ∼27.9 kJ/cm2. Electron temperatures and densities of the ablated plasma were determined by analyzing the time-resolved x-ray spectroscopy data through a comparison of experimental measurements with synthetic results obtained from Si atomic calculations in a steady state and non-local thermodynamic equilibrium. These calculations were computed using PrismSPECT [MacFarlane et al., High Energy Density Phys. 3, 181 (2007)]. Additionally, radiation-hydrodynamics simulations with FLASH are used to generate simulated plasma-density and plasma-temperature profiles, which are then compared with the experimental measurements. Our analyses reveal that increasing the laser pulse length at a constant fluence results in a decrease in electron temperatures and densities. Furthermore, the longer pulses with lower intensities lead to deeper ablation regions before reaching the peak ablation but lower ionization balances in the silicon layer. These findings emphasize the critical role of laser pulse length in plasma ablation and shock generation for laser-impulse studies.

Safety and potential effectiveness of platelet-rich plasma and extracorporeal shock wave therapy in the treatment of erectile dysfunction after nerve-sparing radical prostatectomy in patients: pilot study

Background. Prostate cancer is the most common type of cancer in men. Radical prostatectomy (RPE), including nerve-sparing, often leads to erectile dysfunction and a significant decrease in the quality of life. The available treatments are limited in effectiveness and/or are not suitable for patients.Aim. The aim of the study was to evaluate the safety and effectiveness of platelet-rich plasma (PRP) and extracorporeal shock wave therapy (ESWT) in the treatment of erectile dysfunction in patients after nerve-sparing RPE.Materials and methods. 14 men were included in the study after unilateral or bilateral nerve-sparing RPE more than 3 months ago. The total prostate-specific antigen in all patients was less than 0.2 ng/ml 3 months or more after surgery. Age – 57.8 ± 6.2 (49–72) years, duration of erectile dysfunction – 7.6 ± 3.9 (3–16) months. Two visits per week were out for 6 weeks: in visit 1, the ESWT (Dornier Aries) was performed on penis and injections of PRP into the penis, the muscles involved in the erection were activated at the end of the session by ESWT, in visit 2, ESWT on penis. The examinations were performed on the 0 and 60 days of the study: International Index of Erectile Function (IIEF-5), Sexual Encounter Profile (SEP), Erection Hardness Score (EHS), Global Assessment Questionnaire (GAQ), International Prostate Symptom Score (IPSS), Quality of Life (QoL), total blood testosterone, to penile duplex Doppler ultrasonography (PDDU) with prostaglandin E1 analog. Inclusion criteria were absence of metastases to distant organs and lymph nodes; stage no more than T3b; IIEF-5 less than 21 points after RPE; PSV less than 30 cm/s and/or RI less than 0.8 according to the PDDU after RPE; the presence of erections before RPE.Results. Treatment was tolerated satisfactorily for all patients. Significant improvement of erectile function was noted according to IIEF-5 (p &lt;0.05), SEP (p = 0.002), EHS (p = 0.002). According to GAQ, 11 patients (78.5 %) noted a positive effect of treatment. PSV and RI in both cavernous arteries increased significantly (p &lt;0.05) according PDDU. All patients noted a dysuria decrease based on IPSS (p = 0.007) and QoL (p = 0.58). The concentration of total testosterone in the blood without significant dynamics (p = 0.192).Conclusion. There are positive effects in relation to a significant improvement in erectile function in all patients according to validated questionnaires and PDDU. The proposed treatment is a promising method of restoring patient data. The study continues on a larger sample of patients.

Lamb waves evaluation in CFRP plates with laser shock wave technique

Lamb waves, which are guided waves propagating along the surface of a thin plate structure, have been investigated to remotely perform nondestructive testing for aircraft or infrastructures made of carbon fiber reinforced plastic (CFRP) plates. CFRP plates are prone to internal damage such as delamination, which does not occur in metallic materials. Although nondestructive methods such as X-ray, flash thermography, etc. have been investigated in several studies, they may have some disadvantages such as risks of radiation exposure or limitation in terms of size of the structures to be tested for the former, and heat diffusion for the latter. Laser thermoelasticity can generate Lamb waves remotely and nondestructively. However, the generated Lamb waves have a small amplitude; therefore, hundreds of measurements must be averaged to achieve a sufficient signal-to-noise ratio. For these reasons, it has not yet been demonstrated as possible to detect damage in large CFRP structures within a short time using nondestructive, remote-controlled methods. As a first step towards performing nondestructive tests in CFRP plates, this paper demonstrates the generation of A0 mode Lamb waves in the experimental plate samples using laser-induced plasma (LIP) shock waves. The validity of the proposed system is verified by comparing the phase velocities of Lamb waves in the CFRP plates with three different layups obtained with the proposed system, with the theoretical values obtained analytically. This system can generate vibrations in CFRP plates in frequency ranges of a few hundred kHz and allow to determine the phase velocity of the experimental Lamb waves up to approximately 100 kHz.

Shock induced variable density flows in the vacuum microchannel: I. medium laser fluence

Laser-matter interactions with metal target cause plasma explosion and shock accelerated variable density flow instabilities in the Semiconfined Configuration (SCC). Their study gives deeper insight into the flow instabilities present in all microchannel devices. Blast wave motion along the SCC microchanel causes the Kelvin–Helmholtz (KH) instability and formation of vortex filaments for the critical Reynolds number. Appearing in all shear layers—it affects the fluid transport efficiency. Shear layer acceleration causes a Raleigh-Taylor instability (RTI). Oriented bubble growth by discrete merging indicates anisotropic RTI mixing. Similar RTI flame instability appears in the conversion of chemical energy into electricity affecting microcombustion efficiency. Another case of anisotropic RTI is the flow boiling for cooling of chips and microelectronic devices. The RTI boiling which appears for the critical heat flux is based on rising surface vapor columns (oriented bubble growth) with liquid counterflow (spike prominences) for the critical wavelength at density interface. The RT bubble merging graph trees determine turbulent mixing which affects the heat transfer rates. Bottom-wall turbulent flow in the SCC microchannel causes streaks of the low momentum fluid and formation of hairpin vortex packets with lattice organization. This makes possible to quantify parameters responsible for the evolution of hairpin vortex packets in the microchannel devices. Appearing from the low to the high Reynolds numbers they affect the transport properties, control of the fluid motion, enhancement of mixing, or the separation of fluids. Fluid particle ejecta—thin supersonic jets - evolve into long needle-like jets which start spiraling, helical pairing and swirling in the field of thermal gradients. Such instabilities appear in the microcombustion flame instability and in the space micropropulsion systems. Oscillating and spiral flames appear in the presence of thermal gradient in the microchannel, due to the combined effects of thermal gradient fields and the mixture flow rates.

Study on removal of aluminum alloy oxide film by continuous-nanosecond combined laser with different pulse delays

In this paper, the thermal stresses arising from thermal expansion and the adsorption forces between the oxide film and the substrate are calculated from the one-dimensional heat conduction equation. Comparing the magnitude of the two, the laser cleaning conditions are obtained, and relevant models such as plasma shock wave pressure are established. The plasma plume, surface morphology, and elemental composition of aluminium alloy oxide film removed by continuous-nanosecond combined laser with different nanosecond pulse delays were experimentally investigated. At total laser fluence of 3630.47 J/cm2 (continuous laser fluence of 3628.73 J/cm2 and nanosecond laser fluence of 1.74 J/cm2), the removal effect is better with the increase of pulse delay, and the best removal effect is achieved when the pulse delay is 600 ms. Based on the experimental results, the mechanism of oxide film removal by combined lasers with different pulse delays was discussed, and at least two mechanisms of thermal stress against adsorption and plasma shock wave breaking the oxide layer were present to act.

Non-equilibrium aerodynamics between ionization-wave and shock-wave fronts in millimetre-wave supported detonation

A shock wave driven by discharge plasma propagating in a high-power millimetre-wave beam was investigated both experimentally and numerically. A shadowgraph experiment was used to visualize the shock wave and plasma. The ionization wave front of the plasma preceded the shock wave by 2.0–4.0 mm under conditions of 170 GHz beam frequency, atmospheric pressure, and 1.1 GW m−2 peak power density (power density at the beam axis). Furthermore, a two-dimensional computational fluid dynamics (CFD) simulation considering non-equilibrium temperatures and filamentary plasma structures revealed that an ionization-wave front precedes a shock wave front because the energy relaxation requires a few micro-seconds from vibrational excitation at a plasma front to translational excitation for the shock wave formation. Consequently, the distance between an ionization wave front and shock wave front is 3.8 mm in the two-dimensional CFD simulation, which agreed with the experimental results.

Backstreaming ions at a high Mach number interplanetary shock

Context.Solar Orbiter, a mission developed by the European Space Agency, explores in situ plasma across the inner heliosphere while providing remote-sensing observations of the Sun. The mission aims to study the solar wind, but also transient structures such as interplanetary coronal mass ejections and stream interaction regions. These structures often contain a leading shock wave that can differ from other plasma shock waves, such as those around planets. Importantly, the Mach number of these interplanetary shocks is typically low (1–3) compared to planetary bow shocks and most astrophysical shocks. However, our shock survey revealed that on 30 October 2021, Solar Orbiter measured a shock with an Alfvén Mach number above 6, which can be considered high in this context.Aims.Our study examines particle observations for the 30 October 2021 shock. The particles provide clear evidence of ion reflection up to several minutes upstream of the shock. Additionally, the magnetic and electric field observations contain complex electromagnetic structures near the shock, and we aim to investigate how they are connected to ion dynamics. The main goal of this study is to advance our understanding of the complex coupling between particles and the shock structure in high Mach number regimes of interplanetary shocks.Methods.We used observations of magnetic and electric fields, probe-spacecraft potential, and thermal and energetic particles to characterize the structure of the shock front and particle dynamics. Furthermore, ion velocity distribution functions were used to study reflected ions and their coupling to the shock. To determine shock parameters and study waves, we used several methods, including cold plasma theory, singular-value decomposition, minimum variance analysis, and shock Rankine-Hugoniot relations. To support the analysis and interpretation of the experimental data, test-particle analysis, and hybrid particle in-cell simulations were used.Results.The ion velocity distribution functions show clear evidence of particle reflection in the form of backstreaming ions several minutes upstream. The shock structure has complex features at the ramp and whistler precursors. The backstreaming ions may be modulated by the complex shock structure, and the whistler waves are likely driven by gyrating ions in the foot. Supra-thermal ions up to 20 keV were observed, but shock-accelerated particles with energies above this were not.

Oriented design of wafer-level stacking structures to enhance reliability of laser debonding of thin devices

The laser debonding process in advanced packaging has become a key technology for the debonding of ultra-thin wafers. However, improving the reliability of debonding and efficient removal of adhesive residues from thin and brittle devices remains challenging. Here, we fabricated bonding pairs formed by inorganic responsive layer, thermal buffer layer, and adhesive layer based on a structural design-oriented strategy. Experimental results showed that the thinned device wafers did not show any damage after laser debonding, and the residual adhesive film could be easily torn off. The response layer (a-Si:H) with high temperature resistance and corrosion resistance has strong photosensitivity under the action of ultraviolet laser with a wavelength of 355 nm, and rapidly decomposes to release H2 and polysilicon nanoparticles. The thermal buffer layer is primarily intended to block the heat flow and compensate internal stress. The adhesive layer acts both as an adhesive during temporary bonding and as a barrier to laser-induced gas shock waves and plasma etching of device layers during debonding. This rational structural design contributes to improves the reliability of the laser debonding process and shows great potential for application in the next generation of thin device debonding.

3D MHD Time-dependent Charge State Ionization and Recombination Modeling of the Bastille Day Coronal Mass Ejection

Heavy ion signatures of coronal mass ejections (CMEs) indicate that rapid and strong heating takes place during the eruption and early stages of propagation. However, the nature of the heating that produces the highly ionized charge states often observed in situ is not fully constrained. An MHD simulation of the Bastille Day CME serves as a test bed to examine the origin and conditions of the formation of heavy ions evolving within the CME in connection with those observed during its passage at L1. In particular, we investigate the bimodal nature of the Fe charge state distribution, which is a quintessential heavy ion signature of CME substructure, as well as the source of the highly ionized plasma. We find that the main heating experienced by the tracked plasma structures linked to the ion signatures examined is due to field-aligned thermal conduction via shocked plasma at the CME front. Moreover, the bimodal Fe distributions can be generated through significant heating and rapid cooling of prominence material. However, although significant heating was achieved, the highest ionization stages of Fe ions observed in situ were not reproduced. In addition, the carbon and oxygen charge state distributions were not well replicated owing to anomalous heavy ion dropouts observed throughout the ejecta. Overall, the results indicate that additional ionization is needed to match observation. An important driver of ionization could come from suprathermal electrons, such as those produced via Fermi acceleration during reconnection, suggesting that the process is critical to the development and extended heating of extreme CME eruptions, like the Bastille Day CME.

Autonomous Materials Synthesis Strategies Towards Accelerated Discovery of Novel Functional Nanomaterials for Green Energy Production

Electrocatalysts designed by alloying two or more elements (e.g., transition metals) showed promising enhancement in catalytic activity and durability due to synergistic effects from alloying, such as strain engineering or electron exchange. The potential of the alloying approach is constrained by standard synthesis methods (e.g., wet chemistry and thermal decomposition techniques) due to the governing thermodynamics rules (e.g., miscibility of the different alloying elements). That renders the synthesis of high entropy alloys (HEA), with more than 3 elements, to be complicated and tedious to achieve by those conventional methods.In the presented talk we are presenting different strategies to synthesize metastable high entropy alloys (HEA) and their outstanding catalytic performance towards OER, in correlation to their unique chemistries and structures. Rapid cycling of temperature from room 25 °C to highly elevated levels (1700 °C), in conjunction with ultra-rapid cooling, within milli-second range have been demonstrated by different methods including rapid Joule heating, Intense light flashing, and microwave plasma shock. Our results show successful synthesis of non-noble metals HEA NPs, possessing higher catalytic activity than IrO2 catalyst for OER. The nature of the alloying elements dictates OER activity by promoting different oxidation states of the catalytically active transition metals (e.g., Fe, Ni and Co). In addition, a phenomenal in-situ chemical welding of HEA NP to carbon support, yielded HEA catalysts with two orders of magnitude longer durability than IrO2. Our developed techniques resulted in formation of super-strong metal-carbide bonds “chemically welding” HEA NP to the catalyst support.Synthesis of various HEA catalyst and their electrocatalytic performance screening has been carried out by using liquid handler robots and multi-axes robotic arm systems. Moreover, to optimize the design of materials (structure and chemistry), we are using active learning techniques to evaluate the achieved performance results by applying Gaussian process, followed by applying Bayesian Optimization techniques to propose novel chemistries and structures with a higher probability to achieve further improved performances. The presented the study does not open the door only towards developing novel catalysts for energy production. However, it presents a strategy with multiple successfully demonstrated platforms towards accelerated discovery of novel materials. The high-throughput nature of the synthesis protocols presented in this talk can produce tens of thousands of different novel chemistries, at the same time taken by conventional methods to synthesize just a few, at a minimal energy consumption, cost, and manpower.

Stability analysis of linear ion waves leading to nonlinear shock and soliton structures in a dense quantum plasma with strongly coupled ions and degenerate electrons

In a quantum plasma with strongly coupled ions and Fermi degenerate electron fluids, features of low frequency wave dispersion and nonlinear electrostatic structure formation are explored. Dynamics of strongly coupled ions is considered through a generalized momentum balance equation over the visco-elastic relaxation time for ion correlations and viscosity of ion fluid through shear. Quantum forces associated with degenerate electron fluid include many-particle effect of exchange-correlations, quantum statistical-pressure and quantum recoil effect. The system supports dispersive shock and soliton structures regulated by the Korteweg-de Vries Burger equation and modified-Korteweg-de Varies equation, respectively which are derived and solved analytically. Only monotonic shock structures are observed for a given value of the Burger factorμ. For solitary structures, the amplitude and width depend upon quantum dispersive effects of electrons.

Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length

We present a study of subcritical shocks in a highly collisional laboratory plasma with a dynamically significant magnetic field. Shocks were produced by placing cylindrical obstacles into the supermagnetosonic ( $M_{{\rm MS}} \sim 1.9$ ) outflow from an inverse wire array z-pinch at the MAGPIE pulsed power facility ( $n_{e} \sim 8.5 \times 10^{17}\,{\rm cm}^{-3}$ , $v \sim 45\,{\rm km}\,{\rm s}^{-1}$ ). We demonstrate the existence of subcritical shocks in this regime and find that secondary stagnation shocks form in the downstream which we infer from interferometry and optical Thomson scattering measurements are hydrodynamic in nature. The subcritical shock width is found to be approximately equal to the resistive diffusion length and we demonstrate the absence of a jump in hydrodynamic parameters. Temperature measurements by collective optical Thomson scattering showed little temperature change across the subcritical shock ( ${&lt;}10\,\%$ of the ion kinetic energy) which is consistent with a balance between adiabatic and Ohmic heating and radiative cooling. We demonstrate the absence of subcritical shocks when the obstacle diameter is less than the resistive diffusion length due to decoupling of the magnetic field from the plasma. These findings are supported by magnetohydrodynamic simulations using the Gorgon and AstroBEAR codes and discrepancies between the simulations and experiment are discussed.

Intermittency at Earth's bow shock: Measures of turbulence in quasi-parallel and quasi-perpendicular shocks

Turbulent plasmas such as the solar wind and magnetosheath exhibit an energy cascade that is present across a broad range of scales, from the stirring scale at which energy is injected, down to the smallest scales where energy is dissipated through processes such as reconnection and wave–particle interactions. Recent observations of Earth's bow shock reveal a disordered or turbulent transition region exhibiting features of turbulent dissipation, like reconnecting current sheets. We used observations from magnetospheric multiscale (MMS) over four separate bow shock crossings of varying shock normal angle to characterize turbulence in the shock transition region and how it evolves toward the magnetosheath. These cases studies have been chosen to ensure validity of Taylor's hypothesis, which we discuss in depth. We observe the magnetic spectrum evolving by fitting power laws over many short intervals, finding that the power-law index in the shock transition region is separable from the upstream and downstream plasma, for both quasi-perpendicular and quasi-parallel shocks. Across the shock, we see a change in the breakpoint location between inertial and ion power-law slopes. We also observe the evolution of scale-independent kurtosis of magnetic fluctuations across the shock, finding a reduction of high kurtosis intervals downstream of the shock. Finally, we adapt a method for calculating correlation length to include a high-pass filter, allowing estimates for changes in correlation length across the shock. In a quasi-perpendicular shock, we find the correlation length to be significantly smaller in the magnetosheath than in solar wind; however, the opposite can occur for quasi-parallel shocks.

Energy Repartition and Entropy Generation across the Earth’s Bow Shock: MMS Observations

The evolution of plasma entropy and the process of plasma energy redistribution at the collisionless plasma shock front are evaluated based on the high temporal resolution data from the four Magnetospheric Multiscale spacecraft during the crossing of the terrestrial bow shock. The ion distribution function has been separated into the populations with different characteristic behaviors in the vicinity of the shock: the upstream core population, the reflected ions, the gyrating ions, the ions trapped in the vicinity of the shock, and the downstream core population. The values of ion and electron moments (density, bulk velocity, and temperature) have been determined separately for these populations. It is shown that the solar wind core population bulk velocity slows down mainly in the ramp with the electrostatic potential increase but not in the foot region as it was supposed. The reflected ion population determines the foot region properties, so the proton temperature peak in the foot region is an effect of the relative motion of the different ion populations, rather than an actual increase in the thermal speed of any of the ion population. The ion entropy evaluated showed a significant increase across the shock: the enhancement of the ion entropy occurs in the foot of the shock front and at the ramp, where the reflected ions are emerging in addition to the upstream solar wind ions, the anisotropy growing to generate the bursts of ion-scale electrostatic waves. The entropy of electrons across the shock does not show a significant change: electron heating goes almost adiabatically.

A gas dynamic perspective on particle lifting in electrostatic discharge-like devices using multiphase particle-in-cell approach

Although particle–laden electrostatic discharges are widely used in laboratories as well as in industrial applications, the mechanism of particle lifting for particles initially at rest in such highly unsteady systems is not well understood. A multiphase gas–particle solver is developed using the multiphase particle-in-cell (MP-PIC) approach to emulate the interaction of a compressible shock-dominated gas phase with the dense particle phase. First, the two-way coupled solver is initially used to study the interaction of a planar traveling shock with a vertical curtain of particulates. The gas and particle phase evolution was found to be in good agreement with a similar experimental study in Ling et al. [Phys. Fluids 24, 113301 (2012)]. Second, the MP-PIC code is used to study the interaction of an expanding blast wave with a thick bed of particles. The simulation considered forces such as quasi-steady drag, pressure-gradient, added-mass, Saffman, and Magnus forces. We observe that the vertical liftoff particles close to the shock impingement point in this configuration are associated with the quasi-steady drag, pressure gradient, and added-mass forces. Also, the Saffman lift and Magnus forces contribute to lifting particles located radially farther away from the shock impingement point. In addition, the study finds a decrease in particle lifting efficiency with decreasing plasma kernel length and shock strength.

Interplanetary Shocks between 0.3 and 1.0 au: Helios 1 and 2 Observations

The Helios 1 (H1) and Helios 2 (H2) spacecraft measured the solar winds at a distance between ∼0.3 and 1.0 au from the Sun. With increasing heliocentric distance (r h), the plasma speed is found to increase at ∼34–40 km s−1 au−1 and the density exhibits a sharper fall () compared to the magnetic field magnitude () and the temperature (). Using all available solar wind plasma and magnetic field measurements, we identified 68 and 39 fast interplanetary shocks encountered by H1 and H2, respectively. The overwhelming majority (85%) of the shocks are found to be driven by interplanetary coronal mass ejections (ICMEs). While the two spacecraft encountered more than 73 solar wind high-speed streams (HSSs), only ∼22% had shocks at the boundaries of corotating interaction regions (CIRs) formed by the HSSs. All of the ICME shocks were found to be fast forward (FF) shocks; only four of the CIR shocks were fast reverse shocks. Among all ICME FF shocks (CIR FF shocks), 60% (75%) are quasi-perpendicular with shock normal angles (θ Bn) ≥ 45° relative to the upstream ambient magnetic field, and 40% (25%) are quasi-parallel (θ Bn < 45°). No radial dependences were found in FF shock normal angle and speed. The FF shock Mach number (M ms), magnetic field, and plasma compression ratios are found to increase with increasing r h at the rates of 0.72, 0.89, and 0.98 au−1, respectively. On average, ICME FF shocks are found to be considerably faster (∼20%) and stronger (with ∼28% higher M ms) than CIR FF shocks.