Scaling up the energy of laser-accelerated ions using novel target structures

We present results on laser acceleration of ions using various designs for micro-structured targets. Our analysis compares recent experimental results on ion acceleration at FZD and Los Alamos to extensive realistic large-scale particle-in-cell simulations.
We focus on the electron dynamics leading to an enhancement in ion energy and show how the interplay of target structure and laser pulse parameters such as temporal contrast, peak intensity and pulse duration can be used to increase the ion energy in a robust way.
As two prominent examples we firstly discuss the role of grazing laser interaction with the walls of a conical target structure on the generation of hot electrons and secondly analyse the effect of lateral target size on repeated electron recirculation for simple mass reduced targets.
While the ion acceleration mechanism itself is based on the well-know target normal sheath acceleration mechanism and is thus robust enough for future applications such as radio therapy of tumours, the transfer of laser energy to electron energy is shown to greatly depend on laser parameters and target structure and thus needs detailed analysis using simulations.
In order to connect the electron dynamics during the short time the laser interacts with the electrons to the dynamics of the ion acceleration that evolve on a time scale that is typically three orders of magnitude longer, particle-in-cell simulations up to a few picoseconds duration, equating to some hundred thousand time steps, have been used.