Investigation of beam stability in a high intensity drift tube linac for heavy ion inertial fusion

With the new concept of indirectly driven targets for heavy ion inertial fusion, the driver scenarios had to be reconsidered. A European study group (HIDIF collaboration) investigated the feasibility of a driver facility based on a linac and storage ring approach (Hofmann and Plass (Eds.), GSI-98-06 GEP, Darmstadt, 1998). In a preinjector consisting of an array of ion sources, rf-linacs and funnel devices a 400 mA Bi+ beam is formed, which is further accelerated in a main linac from about 2 GeV to its final energy of 10 GeV and then injected into the rings for storage and pulse compression. The most important requirements for the beam dynamics layout of this high intensity heavy ion linac are transmission rates of nearly 100% and very low emittance growth to avoid particle losses along the linac and at ring injection which may cause radioactivation of the structures. A particle dynamics design of an Alvarez type drift tube linac (DTL) has been successfully carried out with respect to high stability of the beam against errors and mismatch, which was checked by multiparticle simulations. Statistical errors of rf field amplitude and phase and quadrupole gradients were taken into account as well as current fluctuations, initial mismatch modes and changes of particle input distributions and combinations of different errors. Results of Monte Carlo simulations with up to 20,000 particles show a smooth behaviour of the beam and small halo development only. In addition the “telescoping” option, where three different ion species are accelerated, and the necessary modifications for the linac, have been investigated.