Beam distribution homogenization design for laser-driven proton therapy accelerator

CLAPA-II, formerly known as CLAPA-T, is being built by Peking University with the support of China’s Ministry of Science and Technology. The main purpose of this device is to explore and verify the application performance of a laser-driven particle acceleration beam. For proton therapy, it is desirable to have a highly uniform beam distribution during irradiation. Furthermore, according to experimental results and design experience, low particle current will be one of the main challenges in the application of laser beam acceleration. It is important to improve the efficiency of particle transport to increase the particle current available for applications. In order to improve dose uniformity and maximize transport efficiency, we have made an upgrade to our existing beam dynamics design. The modified design keeps the original characteristics of local achromatic transport, but adds a new section for beam homogenization using octupole fields. This beamline can provide continuously-adjustable beam spots at the target point with diameters from 5 mm to 80 mm and energy dispersion of less than 5%. The set of octupoles enables the beam transport system to provide two selectable distributions, which are similar to a Gaussian distribution and a nearly uniform distribution. The beam parameters required by irradiation are taken as the standard, and the results obtained by beam stacking after homogenization have clear advantages. These advantages can improve both the dose uniformity and the beam utilization rate, thereby mitigating the low average particle current from the laser accelerator.