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Abstract:

Relativistic charged particles (CRs for cosmic rays) produced by supernova explosion of the first generation of massive stars that are responsible for the reionization of the universe escape into the intergalactic medium, carrying an electric current. Charge imbalance and induction give rise to a return current, → jt , carried by the cold thermal plasma which tends to cancel the CR current. The electric field, →E = n→ jt , required to draw the collisional return current opposes the outflow of low-energy CRs and ohmically heats the cold plasma. Owing to inhomogeneities in the resistivity, ν (T ), caused by a structure in the temperature, T, of the intergalactic plasma, the electric field possesses a rotational component which sustains Faraday's induction. It is found that a magnetic field is robustly generated throughout intergalactic space at a rate of 10-17 to 10-16GGyr-1, until the temperature of the intergalactic medium is raised by cosmic reionization. The magnetic field may seed the subsequent growth of magnetic fields in the ntergalactic environment. The role of CR-driven instabilities is discussed, and nonlinear effects are briefly considered.

Abstract:

Gamma-ray and electron-positron pair production will figure prominently in laser-plasma experiments with next generation lasers. Using a Monte Carlo approach we show that straggling effects arising from the finite recoil an electron experiences when it emits a high-energy photon, increase the number of pairs produced on further interaction with the laser fields. © 2011 IOP Publishing Ltd.

Abstract:

We present a novel code which solves the Vlasov-Fokker-Planck (VFP) equation in three-dimensional magnetic turbulence using finite difference methods. The approach is distinct from particle tracking codes. The angular component of the velocity space distribution function is represented by a spherical harmonic expansion drawing on an approach pioneered by Bell, et al. (2006 Plasma Phys. Control. Fusion 48 R37) for laser-plasma interaction simulations. This method enables the accurate representation of magnetic fields and of the effect of angular scattering effects on a particle distribution function. The code has been verified against both collisional and quasi-linear turbulent transport theories. It is shown to address successfully the physics of cross-field transport in regimes of magnetic field field perturbation amplitude and collisionality that are difficult to study using other approaches. © 2010 IOP Publishing Ltd.