RESUMEN
A new magnetic field generation mechanism in electrostatic shocks is found, which can produce fields with magnetic energy density as high as 0.01 of the kinetic energy density of the flows on time scales â¼10(4)ωpe-1. Electron trapping during the shock formation process creates a strong temperature anisotropy in the distribution function, giving rise to the pure Weibel instability. The generated magnetic field is well confined to the downstream region of the electrostatic shock. The shock formation process is not modified, and the features of the shock front responsible for ion acceleration, which are currently probed in laser-plasma laboratory experiments, are maintained. However, such a strong magnetic field determines the particle trajectories downstream and has the potential to modify the signatures of the collisionless shock.
RESUMEN
Collisionless shocks are pervasive in astrophysics and they are critical to understand cosmic ray acceleration. Laboratory experiments with intense lasers are now opening the way to explore and characterise the underlying microphysics, which determine the acceleration process of collisionless shocks. We determine the shock character - electrostatic or electromagnetic - based on the stability of electrostatic shocks to transverse electromagnetic fluctuations as a function of the electron temperature and flow velocity of the plasma components, and we compare the analytical model with particle-in-cell simulations. By making the connection with the laser parameters driving the plasma flows, we demonstrate that shocks with different and distinct underlying microphysics can be explored in the laboratory with state-of-the-art laser systems.
RESUMEN
The theoretical model by Sorasio et al. [Phys. Rev. Lett. 96, 045005 (2006)] for the steady state Mach number of electrostatic shocks formed in the interaction of two plasma slabs of arbitrary density and temperature is generalized for relativistic electron and nonrelativistic ion temperatures. We find that the relativistic correction leads to lower Mach numbers and as a consequence ions are reflected with lower energies. The steady state bulk velocity of the downstream population is introduced as an additional parameter to describe the transition between the minimum and maximum Mach numbers that is dependent on the initial density and temperature ratios. In order to transform the solitonlike solution in the upstream region into a shock, a population of reflected ions is considered and differences from a zero-ion temperature model are discussed.
RESUMEN
We show that monoenergetic ion beams can be accelerated by moderate Mach number collisionless, electrostatic shocks propagating in a long scale-length exponentially decaying plasma profile. Strong plasma heating and density steepening produced by an intense laser pulse near the critical density can launch such shocks that propagate in the extended plasma at high velocities. The generation of a monoenergetic ion beam is possible due to the small and constant sheath electric field associated with the slowly decreasing density profile. The conditions for the acceleration of high-quality, energetic ion beams are identified through theory and multidimensional particle-in-cell simulations. The scaling of the ion energy with laser intensity shows that it is possible to generate ~200 MeV proton beams with state-of-the-art 100 TW class laser systems.
