Space–charge effect of laser accelerated protons on beam profile and permanent magnet quadrupole focal line

In a LIGHT project experiment at GSI, the effect of space–charge on the quality of proton beam profile and focal line of permanent magnet quadrupole (PMQ) was investigated experimentally and numerically. In our experiment, the tracking of the real beam (electrons and protons) and pure proton beam (electrons blocked close to the source by a Cu foil) were compared in two schemes: with a mere pinhole collimation and with an additional PMQ. A generated beam distribution close to the experimental results was implemented in TraceWin simulations. In PMQ scheme, a generated field region divided into finite cubic grids with 10μm each side length was used to track the co-propagating electrons. The space–charge effect of the multispecies (protons and electrons) beam was calculated using an electrostatic model. The beam profile expansion in free space and at PMQ focal line was confirmed by simulation.