Core and halo particle dynamics of high intensity proton beams

A very critical design issue for a high intensity proton linac is to keep particle losses below 1 W/m at the high energy end allowing unconstrained hands-on maintenance. For the ESS linac, with it's 214 mA peak current, Monte Carlo simulations with up to one million particles are performed. Single particle trajectories are shown along the linac demonstrating the existence of a space charge potential with non-linear terms and transverse-longitudinal coupling. Radial halo particles at the final energy of 1.334 GeV start at 70 MeV at the boundary of the longitudinal phase space and also transversely close to a boundary of a 4D waterbag distribution. The single particle motion of these halo particles is characterised, on the average, by conservation of the sum of all three emittances. Trajectories are presented for both horizontal-vertical coupling and also transverse-longitudinal coupling. Core particles have a very different behaviour. For core particles, located around the rms emittances at 70 MeV, the single particle emittances can be either increased or decreased.