Development, Characterization, Alignment and Experimental Validation of Partial Sphere Target Arrays for Advanced Proton Acceleration Studies

Proton Fast Ignition is an advanced Inertial Confinement Fusion scheme that is based on decoupling compression and heating of Deuterium-Tritium (DT) fuel, paving a promising path towards higher fusion energy gain with reduced laser requirements. A key challenge in Proton Fast Ignition is generating precisely tailored, high-intensity proton beams, that can deposit the necessary energy into a small volume of the pre-compressed DT fuel. This work addresses this challenge by systematically studying the focusing properties of protons accelerated via Target Normal Sheath Acceleration (TNSA) from partial sphere targets. Past studies in this field have been comparing few target configurations with, at most, tens of shots, massively limiting the statistical evaluation of the data while impeding the exploration of target and laser parameters. To support the medium repetition rate (~1 Hz) experiments, a novel fabrication method was developed to produce 1050 partial sphere targets ranging in three sizes (Ø220 µm, Ø325 µm and Ø525 µm), an unprecedented scale in this domain. Consistent target quality was ensured through comprehensive metrology, including automated individual position measurements of 200 targets mounted in a frame. This enabled the development of a two-stage alignment procedure aimed at achieving rapid turnaround times and ensuring rapid, precise target alignment in the experimental chamber, enabling a repetition rate of 1/3Hz under optimal conditions, an unprecedented feat given the target’s complex geometry. The partial sphere targets were shot at the L-ALEPH laser system at the Colorado State University, resulting in 320 shots across 42 different target configurations. Proton mesh radiography provided energy resolved beam size measurements at distances of ~ 280 µm to 960 µm from the target’s apex, as well as the virtual focus position. Secondary foils, heated by the proton beam at distances of 160 µm to 320 µm from the apex, were observed by an XUV imager. This revealed that smaller, well illuminated partial spheres generated a proton beam with extended collimation, in contrast to larger partial spheres with poorer illumination. These findings validated Particle-in-Cell (PIC) simulations preceding the campaign. This thesis demonstrates reliable large-batch fabrication and fast target alignment in the context of a comprehensive experimental study on the focusing of TNSA protons generated from partial sphere targets. These results enable future large scale parametric studies centered on optimizing proton acceleration and focusing, contributing to the advancement of Proton Fast Ignition research by enabling large parametric studies on the new generation of high energy medium repetition rate facilities.