Temporal evolution of the energy spectrum of proton microbeam guided through an insulating macrocapillary

Abstract

We present theoretical investigation of the temporal evolution of the energy spectrum of ions passing through an insulating capillary. In our simulation we used 1 MeV proton microbeam, and a single, cylindrical shaped polytetrafluoroethylene (PTFE) macrocapillary. In order to prevent the simple geometrical transmission the beam axis was tilted with 1° compared to the capillary axis. According to our simulations, we found that the beam first hit the inner wall of the capillary and build a positive charge patch at a well localized place of the inner capillary surface. As a result, a repulsive electric field is generated for protons enter later into the capillary and a collision-less transmission occurs, which is called ion guiding. We show that our simulated energy spectra are in good agreement with our previous experimental findings.