Longitudinal phase space reconstruction for a heavy ion accelerator

Abstract

At the GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt, Germany, a prototype cryomodule (advanced demonstrator) for the superconducting (SC) continuous wave (CW) Helmholtz Linear Accelerator (HELIAC) is under construction. A transport line, comprising quadrupole lenses, rebuncher cavities, beam correctors, and adequate beam instrumentation has been built to deliver the beam from the GSI 1.4 MeV/u High Charge Injector (HLI) to the advanced demonstrator, which offers a test environment for SC CW multigap cavities. In order to achieve proper phase space matching, the beam from the HLI must be characterized in detail. In a dedicated machine experiment the bunch shape has been measured with a nondestructive bunch shape monitor (BSM). Therefore, different bunch projections were obtained by altering the voltage of two rebunchers. These measurements were combined with dedicated beam dynamics simulations using the particle tracking code dynamion. The longitudinal bunch shape and density distribution at the beginning of the matching line are fully characterized by a tomographic reconstruction method based on a non-negative least square minimization approach.