Sustained Acceleration of Over-dense Plasmas by Colliding Laser Pulses

We review recent PIC simulation results which show that double-sided irradiaton of a thin overdense plasma slab by ultra-intense laser pulses from both sides can lead to sustained comoving acceleration of surface electrons to energies much higher than the conventional ponderomotive limit. The acceleration stops only when the electrons drift transversely out of the laser beam. We show results of parameter studies based on this concept and discuss future laser experiments that can be used to test these computer results.Comment: 9 pages 6 figures. AIP Conference Proceedings for 2005 Varenna Conf. on Superstrong Fields in Plasmas (AIP, NY 2006

Soft gamma rays from black holes versus neutron stars

The recent launches of GRANAT and GRO provide unprecedented opportunities to study compact collapsed objects from their hard x ray and gamma ray emissions. The spectral range above 100 keV can now be explored with much higher sensitivity and time resolution than before. The soft gamma ray spectral data is reviewed of black holes and neutron stars, radiation, and particle energization mechanisms and potentially distinguishing gamma ray signatures. These may include soft x ray excesses versus deficiencies, thermal versus nonthermal processes, transient gamma ray bumps versus power law tails, lines, and periodicities. Some of the highest priority future observations are outlines which will shed much light on such systems

Comoving acceleration of overdense electron-positron plasma by colliding ultra-intense laser pulses

Particle-in-cell (PIC) simulation results of sustained acceleration of electron-positron (e+e-) plasmas by comoving electromagnetic (EM) pulses are presented. When a thin slab of overdense e+e- plasma is irradiated with linear-polarized ultra-intense short laser pulses from both sides, the pulses are transmitted when the plasma is compressed to thinner than ~ 2 relativistic skin depths. A fraction of the plasma is then captured and efficiently accelerated by self-induced JxB forces. For 1 micron laser and 1021Wcm-2 intensity, the maximum energy exceeds GeV in a picosecond.Comment: 10 pages, 4 figure

Parameter study of the diamagnetic relativistic pulse accelerator (DRPA) in slab geometry I: Dependence on initial frequency ratio and slab width

Two-and-a-half-dimensional particle-in-cell plasma simulations are used to study the particle energization in expanding magnetized electron-positron plasmas with slab geometry. When the magnetized relativistic plasma with high temperature (initial electron and positron temperature are $k_{B}T_{e}=k_{B}T_{p}=5MeV$) is expanding into a vacuum, the electromagnetic (EM) pulse with large amplitude is formed and the surface plasma particles are efficiently accelerated in the forward direction owing to the energy conversion from the EM field to the plasma particles. We find that the behavior of the DRPA (Diamagnetic Relativistic Pulse Accelerator) depends strongly on the ratio of the electron plasma frequency to the cyclotron frequency $\omega_{pe}/\Omega_{e}$ and the initial plasma thickness. In the high $\omega_{pe}/\Omega_{e}$ case, the EM pulse is rapidly damped and the plasma diffuses uniformly without forming density peaks because the initial thermal energy of the plasma is much larger than the field energy. On the contrary, in the low $\omega_{pe}/\Omega_{e}$ case, the field energy becomes large enough to energize all the plasma particles, which are confined in the EM pulse and efficiently accelerated to ultrarelativistic energies. We also find that a thicker initial plasma increases the maximum energy of the accelerated particles.Comment: 8 pages, submitted to Physics of Plasma

General Relativistic Magnetohydrodynamic and Monte Carlo Modeling of Sagittarius A*

We present results of models of the physical space and parameters of the accretion disk of Sagittarius A*, as well as simulations of its emergent spectrum. This begins with HARM, a 2D general relativistic magneto-hydrodynamic (GRMHD) model, specifically set up to evolve the space around a black hole. Data from HARM are then fed into a 2D Monte-Carlo (MC) code which generates and tracks emitted photons, allowing for absorption and scattering before they escape the volume.Comment: Accepted for publication in Astrophysics & Space Science, originally presented at HEDLA 201