Shock wave

About: Shock wave is a research topic. Over the lifetime, 36184 publications have been published within this topic receiving 635848 citations. The topic is also known as: Shock waves & shockwave.

A new class of forward‐reverse shock pairs in the solar wind

Abstract: A new class of forward-reverse shock pairs in the solar wind has been discovered using Ulysses observations at high heliographic latitudes. These shock pairs are produced by expansion of coronal mass ejections, CMEs, that have internal pressures that are higher than, and speeds that are comparable to, that of the surrounding solar wind plasma. Of six certain CMEs observed poleward of S31 deg, three have associated shock pairs of this nature. We suggest that high internal CME pressures may exist primarily for events that have high speeds close to the surface of the Sun.

Ion acceleration in non-relativistic astrophysical shocks

Abstract: We explore the physics of shock evolution and particle acceleration in non-relativistic collisionless shocks using hybrid simulations. We analyze a wide range of physical parameters relevant to the acceleration of cosmic rays (CRs) in astrophysical shock scenarios. We show that there are fundamental differences between high and low Mach number shocks in terms of the electromagnetic turbulence generated in the pre-shock zone; dominant modes are resonant with the streaming CRs in the low Mach number regime, while both resonant and non-resonant modes are present for high Mach numbers. Energetic power-law tails for ions in the downstream plasma account for up to 15% of the incoming upstream flow energy, distributed over ~5% of the particles in a power law with slope ?2 ? 0.2 in energy. Quasi-parallel shocks with ? ? 45? are good ion accelerators, while power laws are greatly suppressed for quasi-perpendicular shocks, ? > 45?. The efficiency of conversion of flow energy into the energy of accelerated particles peaks at ? = 15?-30? and MA = 6, and decreases for higher Mach numbers, down to ~2% for MA = 31. Accelerated particles are produced by diffusive shock acceleration (DSA) and by shock drift acceleration (SDA) mechanisms, with the SDA contribution to the overall energy gain increasing with magnetic inclination. We also present a direct comparison between hybrid and fully kinetic particle-in-cell results at early times. In supernova remnant (SNR) shocks, particle acceleration will be significant for low Mach number quasi-parallel flows (MA < 30, ? < 45). This finding underscores the need for an effective magnetic amplification mechanism in SNR shocks.

Nonlinear Particle Acceleration in Oblique Shocks

Abstract: The solution of the nonlinear diffusive shock acceleration problem, where the pressure of the non-thermal population is sufficient to modify the shock hydrodynamics, is widely recognized as a key to understanding particle acceleration in a variety of astrophysical environments. We have developed a Monte Carlo technique for self-consistently calculating the hydrodynamic structure of oblique, steady state shocks, together with the first-order Fermi acceleration process and associated nonthermal particle distributions. This is the first internally consistent treatment of modified shocks that includes cross-field diffusion of particles. Our method overcomes the injection problem faced by analytic descriptions of shock acceleration and the lack of adequate dynamic range and artificial suppression of cross-field diffusion faced by plasma simulations; it currently provides the most broad and versatile description of collisionless shocks undergoing efficient particle acceleration. We present solutions for plasma quantities and particle distributions upstream and downstream of shocks, illustrating the strong differences observed between nonlinear and test particle cases. It is found that, for strong scattering, there are only marginal differences in the injection efficiency and resultant spectra for two extreme scattering modes, namely large-angle scattering and pitch-angle diffusion, for a wide range of shock parameters, i.e., for nonper-pendicular subluminal shocks with field obliquities less than or equal to 75° and de Hoffmann-Teller frame speeds much less than the speed of light.

Heating and Nonthermal Particle Acceleration in Relativistic, Transverse Magnetosonic Shock Waves in Proton-Electron-Positron Plasmas

Abstract: We report the results of one-dimensional particle-in-cell simulations of magnetized ultrarelativistic shock waves in proton-electron-positron plasmas. Relativistic cyclotron instability, as the incoming particles encounter the increasing magnetic field within the shock front provides the basic plasma heating mechanism. The major new results come from simulations with mass ratio mp/m± = 100. When the protons provide a sufficiently large fraction of the upstream flow energy density (including particle kinetic energy and Poynting flux), a substantial fraction of the shock heating goes into the formation of suprathermal power-law spectra of e-e+. Cyclotron absorption by the pairs of the high harmonic ion cyclotron waves, emitted by the protons, provides the nonthermal acceleration mechanism. When the proton fraction is small (pair plasma almost charge-symmetric), the e- and e+ have approximately equal amounts of nonthermal heating. At the lower range of our simulations with mass ratio 100, when the ions contribute 56% of the upstream flow energy flux, the pairs' nonthermal acceleration efficiency by energy is about 1%, increasing to 5% as the ions' energy fraction increases to 72%. When the fraction of upstream flow energy in the ions rises to 84%, the efficiency of nonthermal acceleration of the pairs reaches 30%: the e+ receive most of the nonthermal power and the nonthermal spectra harden. We suggest that the varying power-law spectra observed in synchrotron sources that may be powered by magnetized winds and jets might reflect the correlation of the proton-to-pair content enforced by the underlying electrodynamics of these sources' outflows, and that the observed correlation between the X-ray spectra of rotation-powered pulsars with the X-ray spectra of their nebulae might reflect the same correlation.