Three-dimensional Weibel instability in astrophysical scenarios

Abstract

Near equipartition magnetic fields are predicted by gamma ray bursters models and astronomical observations, in general associated with shocks or regions with colliding streams of particles. These scenarios require the conversion of kinetic energy in the outgoing plasma shells into B-fields. How the magnetic fields are generated and how particles are accelerated is still an open question, that can only be definitely addressed via fully kinetic three-dimensional ͑3D͒ numerical simulations. These shocks are collisionless because dissipation is dominated by wave-particle interactions, i.e., it is accomplished by particle scattering in turbulent electromagnetic fields generated at the shock front, or equivalently the mean free path is much longer than the shock front thickness ͑a few collisionless skin depths or a few Larmor radii, in magnetized plasmas͒. Plasma instabilities driven by streaming particles, such as the Weibel instability, are responsible for the excitation of these turbulent electromagnetic fields. Three-dimensional fully kinetic electromagnetic relativistic particle-in-cell simulations for the collision of two interpenetrating plasma shells were performed using the code OSIRIS ͓Fonseca et al., Lect. Notes Comput. Sci. 2331, 342 ͑2002͔͒, showing ͑i͒ the generation of long-lived near-equipartition quasistatic ͑electro͒magnetic fields, ͑ii͒ nonthermal particle acceleration, and ͑iii͒ short-scale to long-scale B-field evolution. These results may be important to understand magnetic field generation and particle acceleration in relativistic collisionless shock fronts, in gamma ray bursters, pulsar winds, and radio supernovae, and open the way to the full 3D kinetic modeling of relativistic shocks.

Magnetic Field Generation in Relativistic Shocks

“…As both analytical estimates and numerical simulations show, the Weibel instability in pair plasmas can produce a magnetic field of near-equipartition strength (Fonseca et al 2003;Haruki & Sakai 2003;Kazimura et al 1998;Medvedev & Loeb 1999;Yang et al 1994). In numerical simulations, the magnetic field generation always undergoes an exponentially growing phase that agrees with the estimates from linear analytical theory, and enters a nonlinear phase after that.…”

Simulations of relativistic collisionless shocks: shock structure and particle acceleration

“…We usually have c/ω p = 10 cells in the upstream region and simulate domains upto 200 × 40 × 40 skindepth on the side, or 2000 × 400 × 400 cells with several billion particles. 3D PIC codes are currently also used by other groups to study shocks, notably by [4,7,5]. All simulations agree on the general physical processes involved, but groups differ in the setup of the simulations and the length and extent of the runs.…”

Electron streams formation and secondary two stream instability onset in the post-saturation regime of the classical Weibel instability

“…Many authors have focused on the saturation process of the Weibel instability (e.g., Kato 7 and Califano et al 8 ) and, in particular, on the value and persistence in time of the magnetic field, especially in connection with the problem of the generation of magnetic fields in cosmological settings (see Medvedev and Loeb 9 , Califano, Cecchi, and Chiuderi, 10 Schlickeiser and Shukla, 11 Fonseca et al 12 and references therein). On the other hand, the study of the electrostatic activity after saturation has drawn less attention.…”