Fast electrons, filamented laser light, and the fast ignitor

摘要

We report on the absorption of laser energy that results when an ultra-intense laser pulse is incident onto a sharp vacuum-plasma boundary, where the initial shelf density of the plasma is much greater than the critical density, n(sub cr). It is found that 2-D effects greatly increase the amount of absorption into hot electrons, over the amount predicted using 1-D theory. In particular, a scaling for the absorption as a function of density, for a fixed laser intensity, implies that the absorption will be of order 30% for densities well in excess of The interaction is studied using both 1- and 2- dimensional particle-in-cell (PIC) 100 n(sub cr) simulations. The 1-D results agree quite well with a simple scaling of JxB heating, where the laser electric field penetrates a skin depth into the overdense plasma and subsequently heats electrons. In 2-D, when the laser is incident at an angle, the absorption is seen to increase substantially due to a form of resonant absorption that occurs in steep density profiles. We find that the inclusion of kinetic and multi-dimensional effects are crucial to obtaining a complete picture of the interaction. The ability of ultra-intense lasers to produce acceptable amounts of hot electrons necessary for the fast ignitor fusion concept will also be assessed.