Simulated transmission of a 1-MeV proton microbeam through an insulating macrocapillary

Simulations of a 1-MeV proton microbeam transmitted through an insulating macrocapillary were conducted to gather a detailed insight into the related guiding mechanisms. The calculations were performed in view of previous experiments showing guided transmission for a proton beam with a diameter of 2 μm. The simulations are in agreement with the previous results using a microbeam with a divergence of 0.6°, for which guided transmission was observed. This guiding is attributed to the generation of an extended charge patch, producing a broad deflection field along the capillary length. On the other hand, it is found that the transmission of the microbeam without divergence is impossible showing that the divergence plays a decisive role in the guiding process. Further results provide clear evidence that guiding can occur for usual MeV proton beams rather than only for a microbeam.