Figure 3.

(a) Experimental setup (not to scale) used for characterizing the degree of beam collimation achieved by HC targets. Irradiating identical HC targets at similar laser conditions, proton beams were diagnosed by placing the RCF stack at different distances from the interaction foil. The HC targets used in this case were made of 0.125 mm thick Stainless steel wire of internal diameter, pitch and length of $0.7\pm 0.015\text{mm}$, $0.35\pm 0.015\text{mm}$ and $10\pm 0.1\text{mm}$ respectively , designed to synchronise optimally with $\sim$9 MeV protons and post-accelerate them to $\sim$30 MeV. (b–d) show spatial profiles of $\sim$30 MeV proton beams captured by the RCF stack placed at $60\pm 1\text{mm}$, $100\pm 1\text{mm}$ and $200\pm 1\text{mm}$ respectively. (e) shows the 3D dose profile of the proton beam shown in (c).