Tree-code simulations of proton acceleration from laser-irradiated wire targets

Abstract

Recent experiments using Terawatt lasers to accelerate protons deposited on thin wire targets are modeled with a new type of gridless plasma simulation code. In contrast to conventional mesh-based methods, this technique offers a unique capability in emulating the complex geometry and open-ended boundary conditions characteristic of contemporary experimental conditions. Comparisons of ion acceleration are made between the tree code and standard particle-in-cell simulations for a typical collisionless “hole boring” scenario in slab geometry. The utility of the gridless approach is emphasized by a series of simulations in “wire” geometry, in which electrons are permitted to circulate around the target at arbitrary distances from the focal region. The simulations reveal a number of features in common with recent experimental observations, including a disclike emission pattern of the MeV protons accelerated away from the wire.

PIC simulation of a thermal anisotropy-driven Weibel instability in a circular rarefaction wave

“…Our circular plasma cloud corresponds to an idealized cross section of the wire, as long as it is sufficiently far away from the laser impact point [48]. The cross section is idealized, because we do not consider ionization processes that require more elaborate numerical codes [51,52]. The plasma dynamics outside of the wire should be comparable in the simulation and experiment.…”

Progress in Mesh-Free Plasma Simulation With Parallel Tree Codes

“…To set up an FSP simulation with PEPC, the electrons and ions are first brought into a homogeneous equilibrium configuration according to the target geometry, density n 0 , and electron temperature T e [5]. For example, a foil target might be set up with dimensions L x L y L z = 5 × 12 × 12 μm 3 , comprising 3.2 × 10 6 electrons and ions, giving a = 0.7c/ω p .…”

“…Despite their reduced physics content compared to that of the fully electromagnetic PIC codes, the mesh-free tree codes already offer intriguing new possibilities in plasma simulation, for example, in the following: where collisions are important, for modeling complex geometries including strong density gradients, or for mass-limited systems in which artificial boundaries would normally compromise the simulation's validity-for example, atomic clusters ionized by an intense laser pulse. In the Plasma Simulation Laboratory at Jülich Supercomputing Centre, we are developing this technique further to include self-generated magnetic fields and have been using a parallel electrostatic tree code to study the 3-D phenomena in laser and particle beam interactions with various types of complex plasma target [5]- [9].…”

Spatially Resolved Electronic Correlations in Nanoclusters

“…Therefore, any implementation has to be parallelized across more than one processor. The Pretty Efficient Parallel Coulomb Solver (PEPC) has been developed at Jülich Supercomputing Centre for several years [9][10][11][12]. It implements the classical Barnes-Hut algorithm and uses the Hased Oct-Tree scheme originally proposed in [13] for internal representation and parallelization of the tree.…”