Scaling of 3D Printed Microstructured Targets in the Multi-Ps, Quasi-Relativistic Regime for High-Flux Laser-Driven Ion Acceleration

Laser-driven ion acceleration has emerged as a promising technique for producing high-flux, energetic proton beams for applications in high-energy-density science, radiography, and inertial fusion energy concepts like ion fast ignition. Recent advances in target fabrication, notably the use of 3D-printed microstructured arrays with graded density profiles, have demonstrated significant improvements in proton energy and conversion efficiency compared to conventional flat foils, particularly in the highly relativistic laser regime. In this work, we present a detailed experimental scaling study of laser-driven ion acceleration using log-pile microstructured targets in the quasi-relativistic, multi-picosecond regime. Experiments were conducted at the OMEGA-EP facility, utilizing short-pulse laser beams with energies up to 1250 J, pulse durations ranging from 0.6 to 10 ps, and focal spot sizes from 14 to 50 μm, corresponding to normalized vector potentials a0 from approximately 0.7–9.2. Target parameters, including micro-wire diameter (0.5-1 μm) and total thickness (10-50 μm), were systematically varied. Proton spectra and beam profiles were characterized using radiochromic film stacks, while electron spectra were measured with a magnetic spectrometer. Our results show that ion performance metrics such as the maximum proton energy and conversion efficiency scale strongly with target parameters including the target average density. These findings provide important scaling relationships for optimizing target design and laser parameters in future high-flux, laser-driven ion acceleration experiments.