MOMENT-BASED SIMULATION OF THE S-DALINAC RECIRCULATIONS ∗

In this paper an outline of the numerical model and the implementation of the moment-based beam dynamics sim- ulation tool V-Code is presented together with new sim- ulation results regarding the S-DALINAC recirculations. These simulations demonstrate the applicability of the V- Code to properly reproduce the recirculating layout includ- ing the longitudinal beam dynamics within the dispersive sections. So far, the acceleration of the particles within the main linac section is done on crest of the accelerating electric field of the 8 superconducting cavities. Together with an isochronous recirculation scheme, were every particle has the same revolution time L independent of its energy, the field errors coherently add up throughout the three main linac passages. This results in a undesired increase of the energy spread. In order to reduce the energy spread caused by the ob- served phase- and amplitude-jitters a new non-isochronous recirculation scheme is currently being investigated at the IKP. This scheme utilizes longitudinal dispersion DL in the recirculation paths together with an off-crest acceleration as it is done for example in microtrons. The intended longitudinal dispersion leads to the fact that particles with higher energy re-enter the LINAC earlier, whereas particles with lower energy re-enter the LINAC later. In (1) a phase shift of 7.5 degree and a longitudinal dispersion of -1.5 mm/% were found to be an optimal working point for the two S-DALINAC recirculations. Under these conditions the effects of the phase- and amplitude jitters on the energy spread can almost be compensated.