Tony Bell FRS

Abstract:

The transport of fast electrons generated by a 1 ps, 20 J, 10(19) W cm(-2), 1 microm wavelength laser pulse through 70-250 microm thick deuterated polyethylene (CD2) targets is modeled with a Fokker-Planck hybrid code in r-z geometry. Initially, electric field generation inhibits propagation, which then proceeds by the formation of a low resistivity channel due to Ohmic heating. The magnetic field generated at the edge of the channel leads to strong collimation. This is observed for a wide range of parameters. Reflection of electrons at the rear surface forms a magnetic field which focuses the incident electrons on to the rear surface and forces the reflected electrons outwards. This would lead to the formation of a small diameter plasma on the rear surface, as observed in experiments. The reflected electrons are confined to a cone by a self-generated magnetic field, enhancing energy deposition at the rear of the target.

Abstract:

Filamentary ionization tracks have been observed via optical probing inside Al-coated glass targets after the interaction of a picosecond 20-TW laser pulse at intensities above 1019W/cm2. The tracks, up to 700 μm in length and between 10 and 20 μm in width, originate from the focal spot region of the laser beam. Simulations performed with 3D particle-in-cell and 2D Fokker-Planck hybrid codes indicate that the observations are consistent with ionization induced in the glass target by magnetized, collimated beams of high-energy electrons produced during the laser interaction. © 1999 The American Physical Society.