Laser-accelerated protons have a great potential for innovative experiments in radiation biology and chemistry due to the ultra-high dose rate (109 Gy/s) delivered in nanosecond time scale. However, the broad angular divergence around the propagation axis makes them not optimal for applications with stringent requirements on dose homogeneity and total flux at the target. The simplest solution often adopted to increase the homogeneity over a surface is to spread the beam with a flat filter. Such method implies a considerable loss in the total flux over the surface, which is a critical aspect with laser-accelerated proton beams because of the limited charge per bunch available. We demonstrated the use of a Genetic Algorithm assisted approach to design a filter optimally matching the beam parameters. The algorithm can be set to increase the dose homogeneity on an in- vitro biological target while keeping at the same time an acceptable value of average dose per shot. Among different studied configurations we found that a filter placed inside the quadrupole transport system is more efficient than a filter placed after it, allowing a better trade-off between dose homogeneity and average dose at the target. This is explained by the fact that such a filter flattens the beam profile not only through scattering but also by taking advantage of the quadrupole chromaticity to intermingle the proton trajectories. The numerical application to the real case of 7.5 MeV TNSA-driven proton beam will be explained. The presented method allows the production of a laser-driven proton beam fully compatible with radiation biology applications using existing laser sources. Our approach can be further extended to improve spectrum or effective LET homogeneity for thicker targets irradiation.
- L. Pommarel et al. (2017) https://journals.aps.org/prab/abstract/10.1103/PhysRevAccelBeams.20.032801
|Working group||Laser-driven ion acceleration|