Investigation of Focused Laser-Driven Proton Acceleration in the Multi-ps Multi-kilojoule Regime on the National Ignition Facility at Advanced Radiography*

Proton fast ignition (PFI) is an alternative inertial confinement fusion scheme, which relies on using laser-accelerated protons of MeV energies to heat a pre-compressed inertial confinement fusion pellet in order to relax driver energy and symmetry requirements while increasing fuel gain. [1] PFI requires efficient (>10% laser-to-ion coupling) generation of laser-driven protons that can be focused to small (~10s of microns) and deposit tens of kilojoules of energy into the compressed fuel. Given these requirements, multi-kilojoule, multi-picosecond short-pulse laser systems will likely play a role in future PFI schemes. Lasers in this regime,  such as the National Ignition Facility-Advanced Radiographic Capability (NIF-ARC) laser, LFEX-GEKKO laser, PETAL laser and the OMEGA-Extended Performance (EP) laser, which have all been constructed over the last two decades, enable exciting opportunities to test the underlying physics of laser-driven proton acceleration and ion focusing in this regime, which will be crucial for developing and investigating future proton fast ignition platforms for inertial fusion energy. This work presents recent experiments on the NIF-ARC facility where curved hemispherical-shape foils were used for the production of focused laser-driven ion beams, which were subsequently used to isochorically heat a small copper sample. We present both experimental and simulation results understanding ion focusing using hemispherical foils versus traditional flat foils and discuss future experiments on the NIF-ARC to improve proton focusing and heating.

 

[1] M. Roth et al. PRL 86 436 (2001)