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