Laser-ion acceleration using mixed compositions: Tailoring the target for each species

Abstract

Particle-in-cell simulations of laser- ion acceleration demonstrate marked discrepancies in the acceleration experienced by the different ion species in complex target compositions, especially when the target becomes relativistically transparent to the pulse during irradiation. Beginning with proton contaminants in a carbon target, we show how the higher charge-to-mass ratio of the protons results in species stratification and late-time suppression of the carbon acceleration. The target normal sheath acceleration (TNSA) primarily experienced by the protons can be exploited to mitigate this tamping by using a shaped rear surface of the target, leaving the break-out afterburner-driven carbons to accelerate close to the laser axis and then experience less tamping during a late-time TNSA phase. We then explore preferentially accelerating the lighter species in a mixed composition target, particularly focusing on deuteron beam applications. We examine three different target compositions with the same areal electron density, CD2, CH2, and 7LiD, and propose an alternative shaping of the rear surface of 7LiD to increase the number of high-energy deuterons in the beam.