Laser-Driven Proton Acceleration and Focusing using the Orion laser facility

The study of ion acceleration driven by intense (>10²⁰ Wcm^-2) laser-solid interactions has received considerable interest over the past decade, motivated by potential applications of the resulting compact ion source in sectors including industry, medicine and defence. Specifically, the work detailed here is of broad relevance to multiple avenues of high energy density physics, as well as the proton fast ignition (PFI) approach to inertial confinement fusion. Presented is a study of laser-driven proton acceleration and focusing using conical targets. Using the Orion laser system at AWE in the UK, delivering a peak intensity of 10²¹ Wcm^-2, a spectrally broad focused component in the range 10 - 30 MeV is measured, with a clear annular structure in the proton beam's spatial distribution near the cut-off energy. An auxiliary laser-driven proton beam, generated using a second short pulse beam, is used to transversely probe the target, to characterize the field structure responsible for the focusing.

To close in on a realistic PFI scenario, multiple long pulsed beams are used to induce plasma expansion around the cone walls, to measure the effect of a dense, long scale-length plasma on the focusing of the proton beam. This is found to quench any focusing effect.