Skin depth theory for nonlinear-force driven block ignition laser-ICF based on anomalous picosecond terawatt laser-plasma interaction

Abstract

The experiment of Badziak et al has shown that irradiation of copper by 1.5 ps laser pulses produced 50 times lower maximum ion energies than the 22 MeV expected after relativistic self focusing from laser pulses of about ns duration. This discrepancy was confirmed in the following reported experiments specifically designed for this clarification, where MeV Au+30 maximum ion energies needed 400 times higher intensity with ps pulses than with 0.5 ns pulses. Comparing the theory for generating the fastest ions by relativistic self focusing and of the second fastest group by a quiver-collision model, we arrived at the conclusion that the mentioned ps-TW-generated ions are not following these usual theories but that a skin depth model with exclusion of relativistic self focusing explains the experiments. The essential importance is the suppression of the prepulse. We conclude how the experiment by Norreys et al. with the highest ever reported fusion gains may be increased to fusion reactor conditions if our results of prepulse control and suppression of relativistic self focusing would be applied following our skin layer interaction model. This extends the fast ignitor to the nonlinear-force block ignition without plasma precompression.