A simulation study of fast ignition with ultrahigh intensity lasers

The coupling efficiency between the ignition laser and the target core for the fast ignition concept is studied using two-dimensional particle-in-cell simulations. The details of the energy transport within the weakly collisional overdense plasma of a fast ignition target are examined by performing a series of particle-in-cell simulations, where the intensity incident on a 100 times critical plasma with 50 mu m radius is varied between each simulation. The simulations show that the peak energy flux of the ignition electrons is significantly lowered as the electrons traverse the collisionless plasma from the critical density through a weakly collisional overdense plasma region. This allows higher intensity lasers to be used thereby improving the coupling efficiency. In addition, we find that a higher percentage of the ignition laser energy is delivered to the core of the simulation target at higher intensity. The coupling efficiency increases in time during the simulations which are run for 2.5 ps. For a laser intensity of 8x10(20) W/cm(2) the simulations indicate that more than 15% of the incident laser energy is eventually absorbed in a dense plasma core.