Fast electron transport and ionization in a target irradiated by a high power laser

The propagation of relativistic (fast) electrons produced by ultraintense laser irradiation into solid targets is crucial to important fields of laser-plasma study including Fast Ignitor ICF and ion acceleration. In current experiments, targets are initially at room temperature, and there is a need to determine the extent to which the solid-plasma transition affects fast electron transport. A Vlasov-Fokker-Planck code with ionization physics is used to simulate laser-solid interactions around 1018 W cm-2 μm2. Both field and collisional ionization physics is included, and the target is initially unionized. We find that both field and collisional ionization are important to the initial breakdown. After the initial breakdown, collisional ionization continues to ionize the target, and this affects the electric field structure. The effect of continual ionization is for the cold electron distribution to be non-Maxwellian, and for the ionization state to vary throughout the target. This will be important for 'interior' ion acceleration, magnetic field generation and the transverse structure of the fast electron beam