Theory and Modeling of Proton Acceleration on the NIF ARC Laser

Recent experiments fielded at the NIF have focused on characterizing the proton beam that results when the ARC laser is incident on solid density targets.* This facility is unique in that it can shoot 4 beams simultaneously, each of which can contain between 250 J (for a pulse length Lp ~ 1 ps) to 900 J (Lp ~ 30 ps) in a roughly oval spot of ~ 60 microns by 120 microns. Since TNSA is the predominant proton acceleration mechanism, the proton energy spectra depend on not only the rear-side plasma scale length, but also on the hot electron energy distribution. We find that the unique combination of long pulses and large spot sizes allows for the creation of nontrivial amounts of hot electrons with energies well in excess of the ponderomotive potential,** which leads to significant sheath fields, even when moderate ( ~ 1e18 W/cm^2) laser intensities are considered. Combined PIC-LSP simulations compare favorably to experimental results.

* See invited talk by D. Mariscal, this conference.

** See talk by A. J. Kemp et al., this conference.