Relativistic Jets from Accretion Disks

The jets observed to emanate from many compact accreting objects may arise from the twisting of a magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, hydromagnetic jets, which have a significant mass flux and have energy and angular momentum carried by both matter and electromagnetic field and, Poynting jets, where the mass flux is small and energy and angular momentum are carried predominantly by the electromagnetic field. Here, we describe recent theoretical work on the formation of relativistic Poynting jets from magnetized accretion disks. Further, we describe new relativistic, fully-electromagnetic, particle-in-cell simulations of the formation of jets from accretion disks. Analog Z-pinch experiments may help to understand the origin of astrophysical jets.Comment: 7 pages, 3 figures, Proc. of High Energy Density Astrophysics Conf., 200

Parametrization of nonlinear and chaotic oscillations in driven beam-plasma diodes

Nonlinear phenomena in a driven plasma diode are studied using a fluid code and the particle-in-cell simulation code XPDPI. When a uniform electron beam is injected to a bounded diode filled with uniform ion background, the beam is destabilized by the Pierce instability and a perturbation grows to exhibit nonlinear oscillations including chaos. Two standard routes to chaos, period doubling and quasiperiodicity, are observed. Mode lockings of various winding numbers are observed in an ac driven system. A new diagnostic quantity is used to parametrize various nonlinear oscillations.open10

Preliminary Findings from Efforts to Model Pulsed Inductive Theta-Pinch Plasmas Via Particle-In-Cell

A method is pursued to approximately model the electron energy distribution of pulsed inductive plasma devices with Particle-In-Cell code to elucidate formation physics during early times (t \u3c 1 µs). Specifically, reported results from AFRL-Kirtland\u27s pulsed inductive device, FRCHX, are used as a test case to validate results. An r-z slab approximation is outlined and gyro-frequency, Larmor radius, and E×B guiding center drift are verified against theory to within 1% difference. The analyses presented, using both single electron and Particle-In-Cell modeling, agree with FRCHX reported results by showing that average electron kinetic energy does not exceed the ionization threshold of 15.47 eV for gaseous deuterium until after the first ¼ cycle of the ringing pre-ionization stage (when net magnetic field is approximately nullified). These results provide supportive evidence for the concept that bias field actually inhibits ionization if improperly implemente

New simulation capabilities of electron clouds in ion beams with large tune depression

The authors have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and electron clouds (e-clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D ''slice'' e-cloud code POSINST, as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new ''drift-Lorentz'' particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with electron clouds in the High-Current Experiment (HCX). They describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-clouds in the Large Hadron Collider (LHC)