Showing papers on "Shock (mechanics) published in 2014"
TL;DR: In this paper, numerical results on two-and three-dimensional (3D) hydrodynamic core-collapse simulations of an 11.2 M ☉ star are presented, including nine 3D models and fifteen 2D models, exhibiting the revival of the stalled bounce shock, leading to the possibility of explosion.
Abstract: We present numerical results on two- (2D) and three-dimensional (3D) hydrodynamic core-collapse simulations of an 11.2 M ☉ star. By changing numerical resolutions and seed perturbations systematically, we study how the postbounce dynamics are different in 2D and 3D. The calculations were performed with an energy-dependent treatment of the neutrino transport based on the isotropic diffusion source approximation scheme, which we have updated to achieve a very high computational efficiency. All of the computed models in this work, including nine 3D models and fifteen 2D models, exhibit the revival of the stalled bounce shock, leading to the possibility of explosion. All of them are driven by the neutrino-heating mechanism, which is fostered by neutrino-driven convection and the standing-accretion-shock instability. Reflecting the stochastic nature of multi-dimensional (multi-D) neutrino-driven explosions, the blast morphology changes from model to model. However, we find that the final fate of the multi-D models, whether an explosion is obtained or not, is little affected by the explosion stochasticity. In agreement with some previous studies, higher numerical resolutions lead to slower onset of the shock revival in both 2D and 3D. Based on the self-consistent supernova models leading to the possibility of explosions, our results systematically show that the revived shock expands more energetically in 2D than in 3D.
264 citations
TL;DR: In this paper, the authors proposed reliability models for devices subject to dependent competing failure processes of degradation and random shocks with a changing degradation rate according to particular random shock patterns, and considered four different shock patterns that can increase the degradation rate: (i) generalized extreme shock model: when the first shock above a critical value is recorded; (ii) generalized δ-shock model: When the inter-arrival time of two sequential shocks is less than a threshold δ; (iii) generalized m-shock, when m shocks greater than a critical level are recorded; and
Abstract: This article proposes reliability models for devices subject to dependent competing failure processes of degradation and random shocks with a changing degradation rate according to particular random shock patterns. The two dependent failure processes are soft failure due to continuous degradation, in addition to sudden degradation increases caused by random shocks, and hard failure due to the same shock process. In complex devices such as Micro-Electro-Mechanical Systems the degradation rate can change when the system becomes more susceptible to fatigue and deteriorates faster, as a result of withstanding shocks. This article considers four different shock patterns that can increase the degradation rate: (i) generalized extreme shock model: when the first shock above a critical value is recorded; (ii) generalized δ-shock model: when the inter-arrival time of two sequential shocks is less than a threshold δ; (iii) generalized m-shock model: when m shocks greater than a critical level are recorded; and (iv)...
208 citations
TL;DR: In this article, four axisymmetric core-collapse supernova simulations for 12, 15, 20, and 25 $M_\odot$ progenitors were presented.
Abstract: We present four ab initio axisymmetric core-collapse supernova simulations for 12, 15, 20, and 25 $M_\odot$ progenitors All of the simulations yield explosions and have been evolved for at least 12 seconds after core bounce and 1 second after material first becomes unbound Simulations were computed with our Chimera code employing spectral neutrino transport, special and general relativistic transport effects, and state-of-the-art neutrino interactions Continuing the evolution beyond 1 second allows explosions to develop more fully and the processes powering the explosions to become more clearly evident We compute explosion energy estimates, including the binding energy of the stellar envelope outside the shock, of 034, 088, 038, and 070 B ($10^{51}$ ergs) and increasing at 003, 015, 019, and 052 B s$^{-1}$, respectively, for the 12, 15, 20, and 25 $M_\odot$ models Three models developed pronounced prolate shock morphologies, while the 20 $M_\odot$ model, though exhibiting lobes and accretion streams like the other models, develops an approximately spherical, off-center shock as the explosion begins and then becomes moderately prolate $\sim$600 ms after bounce This reduces the explosion energy relative to the other models by reducing mass accretion during the critical explosion power-up phase We examine the growth of the explosion energy in our models through detailed analyses of the energy sources and flows We find that the 12 and 20 $M_\odot$ models have explosion energies comparable to that of the lower range of observed explosion energies while the 15 and 25 $M_\odot$ models are within the range of observed explosion energies, particularly considering the rate at which their explosion energies are increasing The ejected $^{56}$Ni masses given by our models are all within observational limits as are the proto-neutron star masses and kick velocities (Truncated)
207 citations
174 citations
TL;DR: In this article, the fraction of ions that are accelerated to non-thermal energies at non-relativistic collisionless shocks is characterized using kinetic hybrid simulations, and the minimum energy needed for injection into diffusive shock acceleration is calculated as a function of the shock inclination.
Abstract: We use kinetic hybrid simulations (kinetic ions-fluid electrons) to characterize the fraction of ions that are accelerated to non-thermal energies at non-relativistic collisionless shocks. We investigate the properties of the shock discontinuity and show that shocks propagating almost along the background magnetic field (quasi-parallel shocks) reform quasi-periodically on ion cyclotron scales. Ions that impinge on the shock when the discontinuity is the steepest are specularly reflected. This is a necessary condition for being injected, but it is not sufficient. Also, by following the trajectories of reflected ions, we calculate the minimum energy needed for injection into diffusive shock acceleration, as a function of the shock inclination. We construct a minimal model that accounts for the ion reflection from quasi-periodic shock barrier, for the fraction of injected ions, and for the ion spectrum throughout the transition from thermal to non-thermal energies. This model captures the physics relevant for ion injection at non-relativistic astrophysical shocks with arbitrary strengths and magnetic inclinations, and represents a crucial ingredient for understanding the diffusive shock acceleration of cosmic rays.
142 citations
TL;DR: In this paper, the effect of laser shock peening without coating parameters on the microstructural evolution, and dislocation configurations induced by ultra-high plastic strains and strain rates was investigated.
130 citations
TL;DR: In this paper, the entrainment performance and the shock wave structures in a three-dimensional ejector were investigated by Computational Fluid Dynamics (CFD) and Schlieren flow visualization.
Abstract: The entrainment performance and the shock wave structures in a three-dimensional ejector were investigated by Computational Fluid Dynamics (CFD) and Schlieren flow visualization. The ejector performance was evaluated based on the mass flow rates of the primary and secondary flows. The shock wave structures in the ejector mixing chamber were captured by the optical Schlieren measurements. The results show that the expansion waves in the shock train do not reach the mixing chamber wall when the ejector is working at the sub-critical mode. Decreasing of the shock wave wavelength increases the secondary mass flow rate. A three-dimensional CFD model with four turbulence models was then compared with the experimental data. The results show that the RNG k - e model agrees best with measurements for predictions of both the mass flow rate and shock wave structures.
117 citations
TL;DR: In this article, the results of a study of the crushing behavior of open-cell Al foams under impact were presented. But the results were limited to the case of high-speed impacts at velocities in the range of 20 to 160m/s.
115 citations
TL;DR: In this article, the authors investigated the dynamical and spectral evolution of Tycho's SNR by carrying out hydrodynamical simulations that include diffusive shock acceleration of particles in the amplified magnetic field at the forward shock of the SNR.
Abstract: Tycho's supernova remnant (SNR) is well-established as a source of particle acceleration to very high energies. Constraints from numerous studies indicate that the observed γ-ray emission results primarily from hadronic processes, providing direct evidence of highly relativistic ions that have been accelerated by the SNR. Here we present an investigation of the dynamical and spectral evolution of Tycho's SNR by carrying out hydrodynamical simulations that include diffusive shock acceleration of particles in the amplified magnetic field at the forward shock of the SNR. Our simulations provide a consistent view of the shock positions, the nonthermal emission, the thermal X-ray emission from the forward shock, and the brightness profiles of the radio and X-ray emission. We compare these with the observed properties of Tycho to determine the density of the ambient material, the particle acceleration efficiency and maximum energy, the accelerated electron-to-proton ratio, and the properties of the shocked gas downstream of the expanding SNR shell. We find that evolution of a typical Type Ia supernova in a low ambient density (n 0 ~ 0.3 cm–3), with an upstream magnetic field of ~5 μG, and with ~16% of the SNR kinetic energy being converted into relativistic electrons and ions through diffusive shock acceleration, reproduces the observed properties of Tycho. Under such a scenario, the bulk of observed γ-ray emission at high energies is produced by π0-decay resulting from the collisions of energetic hadrons, while inverse-Compton emission is significant at lower energies, comprising roughly half of the flux between 1 and 10 GeV.
111 citations
TL;DR: In this article, the authors examined the second detonation of the double detonation scenario using a combination of analytic and numeric techniques and found that the critical imploding shock strengths needed to achieve a core C detonation are known.
Abstract: The progenitor channel responsible for the majority of Type Ia supernovae is still uncertain. One emergent scenario involves the detonation of a He-rich layer surrounding a C/O white dwarf, which sends a shock wave into the core. The quasi-spherical shock wave converges and strengthens at an off-center location, forming a second, C-burning, detonation that disrupts the whole star. In this paper, we examine this second detonation of the double detonation scenario using a combination of analytic and numeric techniques. We perform a spatially resolved study of the imploding shock wave and outgoing detonation and calculate the critical imploding shock strengths needed to achieve a core C detonation. We find that He detonations in recent two-dimensional simulations yield converging shock waves that are strong enough to ignite C detonations in high-mass C/O cores, with the caveat that a truly robust answer requires multi-dimensional detonation initiation calculations. We also find that convergence-driven detonations in low-mass C/O cores and in O/Ne cores are harder to achieve and are perhaps unrealized in standard binary evolution.
108 citations
TL;DR: In this paper, a dynamic X-FEM model is developed in which both Crank-Nicolson and Newmark time integration methods are used for calculating transient responses of thermal and electromechanical fields respectively.
TL;DR: In this paper, the authors present theoretical analysis and experimental results concerning the major physical issues in the shock-ignition approach, which are the following: generation of a high amplitude shock in the imploding target, laser-plasma interaction physics under the conditions of high laser intensities needed for high-amplitude shock excitation, symmetry and stability of the shock propagation, role of fast electrons in the symmetrization of shock pressure and the fuel preheat.
Abstract: The paper presents theoretical analysis and experimental results concerning the major physical issues in the shock-ignition approach. These are the following: generation of a high amplitude shock in the imploding target, laser–plasma interaction physics under the conditions of high laser intensities needed for high amplitude shock excitation, symmetry and stability of the shock propagation, role of fast electrons in the symmetrization of the shock pressure and the fuel preheat. The theoretical models and numerical simulations are compared with the results of specially designed experiments on laser plasma interaction and shock excitation in plane and spherical geometries.
TL;DR: In this paper, the complex self-sustained oscillations arising from the interaction of an oblique shock with a flexible panel in both the inviscid and viscous regimes have been investigated numerically.
TL;DR: In this paper, the authors present the first stereoscopic and Doppler observations of simultaneous transverse oscillations of a prominence and a filament and longitudinal oscillation of another filament launched by a single shock wave.
Abstract: We present the first stereoscopic and Doppler observations of simultaneous transverse oscillations of a prominence and a filament and longitudinal oscillation of another filament launched by a single shock wave. Using H alpha Doppler observations, we derive the three-dimensional oscillation velocities at different heights along the prominence axis. The results indicate that the prominence has a larger oscillation amplitude and damping time at higher altitude, but the periods at different heights are the same (i.e., 13.5 minutes). This suggests that the prominence oscillates like a linear vertical rigid body with one end anchored on the Sun. One of the filaments shows weak transverse oscillation after the passing of the shock, which is possibly due to the low altitude of the filament and the weakening (due to reflection) of the shock wave before the interaction. Large-amplitude longitudinal oscillation is observed in the other filament after the passing of the shock wave. The velocity amplitude and period are about 26.8 kms(-1) and 80.3 minutes, respectively. We propose that the orientation of a filament or prominence relative to the normal vector of the incoming shock should be an important factor for launching transverse or longitudinal filament oscillations. In addition, the restoring forces of the transverse prominence are most likely due to the coupling of gravity and magnetic tension of the supporting magnetic field, while that for the longitudinal filament oscillation is probably the resultant force of gravity and magnetic pressure.
TL;DR: In this article, the authors used two-and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number (M < 5) shocks and found that about 15 percent of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p~2.4.
Abstract: Electron acceleration to non-thermal energies in low Mach number (M<5) shocks is revealed by radio and X-ray observations of galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with M=3 and a quasi-perpendicular pre-shock magnetic field. We find that about 15 percent of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p~2.4. Initially, thermal electrons are energized at the shock front via shock drift acceleration. The accelerated electrons are then reflected back upstream, where their interaction with the incoming flow generates magnetic waves. In turn, the waves scatter the electrons propagating upstream back toward the shock, for further energization via shock drift acceleration. In summary, the self-generated waves allow for repeated cycles of shock drift acceleration, similarly to a sustained Fermi-like process. This mechanism offers a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.
TL;DR: In this article, a large-eddy simulation of a normal shock train in a constant-area isolator model (M∞=161, Reθ≈1660) is carried out to investigate solution sensitivity with respect to a variety of physical modeling assumptions.
Abstract: Large-eddy simulation of a normal shock train in a constant-area isolator model (M∞=161, Reθ≈1660) is carried out to investigate solution sensitivity with respect to a variety of physical modeling assumptions Simulations with spanwise periodic boundary conditions are first performed, the results of which are compared with experiment and validated with a three-level grid refinement study Due to the computational cost associated with resolving near-wall structures, the large-eddy simulation is run at a Reynolds number lower than that in the comparison experiment; thus, the confinement effect of the turbulent boundary layers is not exactly duplicated Although this discrepancy is found to affect the location of the first normal shock, the overall structure of the shock train and its interaction with the boundary layers matches the experiment quite closely Observations of pertinent physical phenomena in the experiment, such as a lack of reversed flow in the mean and the development of secondary shear laye
TL;DR: In this paper, the authors used micromechanically accurate foam models to simulate and study the dynamic crushing of open-cell foams and found that the transition from quasi-static to nearly planar shocks is rather gradual.
TL;DR: In this article, the authors present a nonlinear Monte Carlo model of efficient diffusive shock acceleration where the magnetic turbulence responsible for particle diffusion is calculated self-consistently from the resonant cosmic-ray (CR) streaming instability, together with non-resonant short-and long-wavelength CR-current-driven instabilities.
Abstract: We present a nonlinear Monte Carlo model of efficient diffusive shock acceleration where the magnetic turbulence responsible for particle diffusion is calculated self-consistently from the resonant cosmic-ray (CR) streaming instability, together with non-resonant short- and long-wavelength CR-current-driven instabilities. We include the backpressure from CRs interacting with the strongly amplified magnetic turbulence which decelerates and heats the super-Alfvenic flow in the extended shock precursor. Uniquely, in our plane-parallel, steady-state, multi-scale model, the full range of particles, from thermal (~eV) injected at the viscous subshock to the escape of the highest energy CRs (~PeV) from the shock precursor, are calculated consistently with the shock structure, precursor heating, magnetic field amplification, and scattering center drift relative to the background plasma. In addition, we show how the cascade of turbulence to shorter wavelengths influences the total shock compression, the downstream proton temperature, the magnetic fluctuation spectra, and accelerated particle spectra. A parameter survey is included where we vary shock parameters, the mode of magnetic turbulence generation, and turbulence cascading. From our survey results, we obtain scaling relations for the maximum particle momentum and amplified magnetic field as functions of shock speed, ambient density, and shock size.
TL;DR: In this article, non-equilibrium molecular dynamics (NEMD) simulations of shock wave compression along the [001] direction in monocrystalline Tantalum, including pre-existing defects which act as dislocation sources, are presented.
TL;DR: In this article, the authors used a simple model of the isolator comprising a vertical spring coupled to two horizontal springs, which is configured to reduce the dynamic stiffness and hence increase the frequency range of isolation.
TL;DR: In this article, the authors studied the initiation of cracks in the thermal shock problem through the variational analysis of the quasi-static evolution of a gradient damage model and derived the periodic distribution of so-initiated cracks and calculated the crack spacing in terms of the material and loading parameters.
Abstract: This paper studies the initiation of cracks in the thermal shock problem through the variational analysis of the quasi-static evolution of a gradient damage model. We consider a two-dimensional semi-infinite slab with an imposed temperature drop on its free surface. The damage model is formulated in the framework of the variational theory of rate-independent processes based on the principles of irreversibility, stability and energy balance. In the case of a sufficiently severe shock, we show that damage immediately occurs and that its evolution follows first a fundamental branch without localization. Then it bifurcates into another branch in which damage localization will take place finally to generate cracks. The determination of the time and mode of that bifurcation allows us to explain the periodic distribution of the so-initiated cracks and to calculate the crack spacing in terms of the material and loading parameters. Numerical investigations complete and quantify the analytical results.
TL;DR: In this article, the authors present an approach to direct-drive inertial confinement fusion (ICF) in which the stages of compression and hot spot formation are partly separated, and show potentials for high gain at laser energies below 1?MJ, and could be tested on the National Ignition Facility or Laser MegaJoule.
Abstract: Shock ignition is an approach to direct-drive inertial confinement fusion (ICF) in which the stages of compression and hot spot formation are partly separated. The fuel is first imploded at a lower velocity than in conventional ICF. Close to stagnation, an intense laser spike drives a strong converging shock, which contributes to hot spot formation. Shock ignition shows potentials for high gain at laser energies below 1?MJ, and could be tested on the National Ignition Facility or Laser MegaJoule. Shock ignition principles and modelling are reviewed in this paper. Target designs and computer-generated gain curves are presented and discussed. Limitations of present studies and research needs are outlined.
TL;DR: In this article, a fully coupled numerical approach with combined Lagrangian and Eulerian methods, incorporating the explosion processes, is performed to model the concrete material behavior subjected to blast loading.
12 Jun 2014-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of LSP on some mechanical properties of a near-α titanium alloy Ti834 was evaluated by using a Vickers indenter and the depth profiles of subsurface micro-hardness of the shocked region were determined through the electro-polishing material removal in steps of 0.1mm.
Abstract: Laser shock peening (LSP) or Laser shock processing is a novel surface treatment technique for strengthening metal materials. In this work, several investigations were performed to evaluate the effect of LSP on some mechanical properties of a near-α titanium alloy Ti834. Micro-hardness measurements of the untreated and LSP treated specimens were carried out by using a Vickers indenter. The depth profiles of subsurface micro-hardness of the shocked region were determined through the electro-polishing material removal in steps of 0.1 mm. It is observed that the micro-hardness of Ti834 alloy can be improved by LSP, and repeated shocks have a very beneficial effect on surface hardening. Residual stress distribution as a function of depth was determined by X-ray diffraction (XRD) with the sin 2 ψ method. The high-cycle fatigue performance of the alloy was investigated and the fractographs of fatigue specimens were observed by SEM. Results reveal that the high-cycle fatigue life of Ti834 alloy increases after laser shock peening due to the introduction of compressive stress which can delay the initiation and growth of the fatigue crack.
TL;DR: In this article, the authors analyzed the resonant radiation emitted by dispersive shock waves owing to higher-order dispersive corrections of the leading term in the defocusing nonlinear Schrodinger equation.
Abstract: We analyze resonant radiation emitted by dispersive shock waves owing to higher-order dispersive corrections of the leading term in the defocusing nonlinear Schrodinger equation. We give criteria for calculating the radiated frequency based on an analytical estimate of the shock velocity and reveal a diversity of scenarios controllable via the corrections, ranging from the radiation-induced transition of the dispersive shock into a classical-type shock to the qualitative modification of the underlying gradient catastrophe or the competition between different breaking mechanisms.
TL;DR: The first measurements of the formation and structure of a magnetized collisionless shock by a laser-driven magnetic piston in a current-free laboratory plasma were reported in this article. But their results were limited to the case of a single piston.
Abstract: We report the first measurements of the formation and structure of a magnetized collisionless shock by a laser-driven magnetic piston in a current-free laboratory plasma. This new class of experiments combines a high-energy laser system and a large magnetized plasma to transfer energy from a laser plasma plume to the ambient ions through collisionless coupling, until a self-sustained MA∼ 2 magnetosonic shock separates from the piston. The ambient plasma is highly magnetized, current free, and large enough (17 m × 0.6 m) to support Alfven waves. Magnetic field measurements of the structure and evolution of the shock are consistent with two-dimensional hybrid simulations, which show Larmor coupling between the debris and ambient ions and the presence of reflected ions, which provide the dissipation. The measured shock formation time confirms predictions from computational work.
01 Jan 2014
TL;DR: This approach combines the good properties of the discontinuous Galerkin method in smooth parts of the flow with the perfect properties of a total variation diminishing finite volume method for resolving shocks without spurious oscillations.
Abstract: We present a shock capturing procedure for high order discontinuous Galerkin methods, by which shock regions are refined and treated by the finite volume techniques. Hence, our approach combines the good properties of the discontinuous Galerkin method in smooth parts of the flow with the perfect properties of a total variation diminishing finite volume method for resolving shocks without spurious oscillations. Due to the subcell approach the interior resolution on the discontinuous Galerkin grid cell is preserved and the number of degrees of freedom remains the same. In this paper we focus on an implementation of this coupled method and show our first results.
TL;DR: In this article, the authors present a numerical study of nanosecond pulsed dielectric barrier discharge (DBD) actuator operating in quiescent air at atmospheric condition.
Abstract: We present a numerical study of nanosecond pulsed dielectric barrier discharge (DBD) actuator operating in quiescent air at atmospheric condition. Our study concentrates on plasma discharge induced fluid dynamics and on exploration of parametric space of interest for voltage pulse in an attempt to shed some light into elucidation of the mechanisms whereby the generated shock wave propagates through and affects the external flow. Specifically, a one-dimensional, self-similar, local ionization kinetic model recently developed to predict key parameters of nanosecond pulsed plasma discharge is coupled with the compressible Navier-Stokes equations possibly for the first time. Within the considered range of parameters of the plasma model which is justified for the modeling of surface nanosecond pulsed discharge at atmospheric pressure, our coupled method is able to provide satisfactory prediction of the shock structure generated by the actuator for comparison with experiment, not only in the qualitative shock wave shape but also in quantitative shock front displacement. We provide a comprehensive analysis of the gas heating, shock wave initiation and evolution processes. For example, the characteristic time of the rapid localized heating responsible for shock wave generation, which is yet to be quantified experimentally, is found to be ∼350 ns. We conduct a parametric investigation by varying the peak voltage from 10 kV to 50 kV and rise time from 5 ns to 150 ns. The pressure wave whose behavior is found to be dominated by input voltage amplitude, introduces highly transient, localized disturbance to the quiescent air. In addition, the vortex induced by the shock passage is relatively weak. The interplay of the induced flows by a few successive plasma discharges operating at continuous mode does not appear to be significant, especially at low voltage amplitude.
TL;DR: In this article, quantum molecular dynamics calculations of principal, porous, and double shock Hugoniots, release isentropes, and sound velocity behind the shock front for aluminum are presented.
Abstract: We present quantum molecular dynamics calculations of principal, porous, and double shock Hugoniots, release isentropes, and sound velocity behind the shock front for aluminum. A comprehensive analysis of available shock-wave data is performed; the agreement and discrepancies of simulation results with measurements are discussed. Special attention is paid to the melting region of aluminum along the principal Hugoniot; the boundaries of the melting zone are estimated using the self-diffusion coefficient. Also, we make a comparison with a high-quality multiphase equation of state for aluminum. Independent semiempirical and first-principle models are very close to each other in caloric variables (pressure, density, particle velocity, etc.) but the equation of state gives higher temperature on the principal Hugoniot and release isentropes than ab initio calculations. Thus, the quantum molecular dynamics method can be used for calibration of semiempirical equations of state in case of lack of experimental data.
TL;DR: In this paper, it was shown that an electromagnetic Weibel shock always forms when two relativistic collisionless, initially unmagnetized, plasma shells encounter, and the predicted shock formation time is in good agreement with 2D and 3D particle-in-cell simulations of counterstreaming pair plasmas.
Abstract: Collisionless shocks in plasmas play an important role in space physics (Earth's bow shock) and astrophysics (supernova remnants, relativistic jets, gamma-ray bursts, high energy cosmic rays). While the formation of a fluid shock through the steepening of a large amplitude sound wave has been understood for long, there is currently no detailed picture of the mechanism responsible for the formation of a collisionless shock. We unravel the physical mechanism at work and show that an electromagnetic Weibel shock always forms when two relativistic collisionless, initially unmagnetized, plasma shells encounter. The predicted shock formation time is in good agreement with 2D and 3D particle-in-cell simulations of counterstreaming pair plasmas. By predicting the shock formation time, experimental setups aiming at producing such shocks can be optimised to favourable conditions.