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

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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 ontemporary 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 disc-like emission pattern of the MeV protons accelerated away from the wire.status: publishe