Halo containment in the ESS linac to ring transfer line

The key issue of the accelerator part of the European Spallation Source ESS is the loss free ring injection. For achieving this goal, the linac beam has to be collimated in both transverse planes and limited in energy spread. By a bunch rotation cavity, positioned 75 m after the linac, the energy spread is reduced by a factor 3. In addition the mean kinetic energy has to be ramped during the injection pulse. For a bunch current of 214 mA, space charge forces are present in all 3 planes. They act quite drastically longitudinally due to the lack of focusing. After the bunch rotation cavity, where the bunch length is larger than the pipe radius, image forces in all 3 planes can no longer be neglected. In order to fulfill the collimation requirements for loss free ring injection under various beam current conditions, transverse beam scraping and a longitudinal two stage collimation system are foreseen. There are two independently phased cavities, one for energy ramping and another for bunch rotation. The bunc...