Electrostatic Structures in Space Plasmas: Stability of Two-dimensional Magnetic Bernstein-Greene-Kruskal Modes

Electrostatic structures have been observed in many regions of space plasmas, including the solar wind, the magnetosphere, the auroral acceleration region, and in association with shocks, turbulence, and magnetic reconnection. Due to potentially large amplitude of electric fields within these structures, their effects on particle heating, scattering, or acceleration can be important. One possible theoretical description of some of these structures is the concept of Bernstein-Greene-Kruskal (BGK) modes, which are exact nonlinear solutions of the Vlasov-Poisson system of equations in collisionless kinetic theory. BGK modes have been studied extensively for many decades, predominately in one dimension (1D), although there have been observations showing that some of these structures have clear 3D features. While there have been approximate solutions of higher dimensional BGK modes, an exact 3D BGK mode solution in a finite magnetic field has not been found yet. Recently we have constructed exact solutions of 2D BGK modes in a magnetized plasma with finite magnetic field strength in order to gain insights of the ultimate 3D theory [Ng, Bhattacharjee, and Skiff, Phys. Plasmas 13, 055903 (2006)]. Based on the analytic form of these solutions, as well as Particle-in-Cell (PIC) simulations, we will present numerical studies of their stability for different levels of background magnetic field strength.Comment: Submitted to AIP Journal Proceedings for "Tenth Annual International Astrophysics Conference

Inductive and Electrostatic Acceleration in Relativistic Jet-Plasma Interactions

We report on the observation of rapid particle acceleration in numerical simulations of relativistic jet-plasma interactions and discuss the underlying mechanisms. The dynamics of a charge-neutral, narrow, electron-positron jet propagating through an unmagnetized electron-ion plasma was investigated using a three-dimensional, electromagnetic, particle-in-cell computer code. The interaction excited magnetic filamentation as well as electrostatic plasma instabilities. In some cases, the longitudinal electric fields generated inductively and electrostatically reached the cold plasma wave-breaking limit, and the longitudinal momentum of about half the positrons increased by 50% with a maximum gain exceeding a factor of 2 during the simulation period. Particle acceleration via these mechanisms occurred when the criteria for Weibel instability were satisfied.Comment: Revised for Phys. Rev. Lett. Please see publised version for best graphic

Chiral symmetry breaking in a uniform external magnetic field II. Symmetry restoration at high temperatures and chemical potentials

Chiral symmetry is dynamically broken in quenched, ladder QED at weak gauge couplings when an external magnetic field is present. In this paper, we show that chiral symmetry is restored above a critical chemical potential and the corresponding phase transition is of first order. In contrast, the chiral symmetry restoration at high temperatures (and at zero chemical potential) is a second order phase transition.Comment: Latex; 12 pages; 8 postscript figures include