GSI, Darmstadt
Increasing the intensity of heavy ion beams in synchrotrons, especially in the low and intermediate energy range, requires a reduction of the charge state. With an increase of two orders of magnitude compared to the present intensity levels at GSI, the FAIR project is aiming for the highest heavy ion beam intensities world wide. Space charge limits and significant beam loss in stripper stages disable a continuation of the present high charge state operation. The presently achieved level of heavy ion beam intensities is in the order of 109 heavy ions per cycle. The FAIR intensities of 1011 heavy ions per cycle can only be reached by acceleration of U28+-ions instead of U73+-ions. Meanwhile, after partially completing the upgrade program of SIS18, the number of U28+-ions accelerated to the SIS100 injection energy, could be increased by a factor of 70. The specific challenge of the intermediate charge state operation is the high cross section for ionization in combination with gas desorption processes and the dynamic vacuum pressure. The achieved progress in minimizing the ionization beam loss underlines that the chosen technical strategies described in this report are appropriate.
GSI, Darmstadt
IAP, Frankfurt am Main
The StrahlSim code was developed to simulate dynamic vacuum effects and charge exchange beam loss in heavy ion accelerators. The code accounts for the charge exchange cross sections at the actual beam energy, the loss positions of charge exchanged ions, and the pressure rise caused by desorption due to the impact of these ions onto the vacuum chamber. Recent progress was made by implementing time dependent longitudinal pressure profiles in StrahlSim. This allows to simulate localized pressure bumps during a cycle and therefore to estimate the lifetime of NEG-coated surfaces depending on their positions in the ring, and the corresponding influence on the beam performance over the saturation process. The new code was applied to SIS18 considering two scenarios. One calculation has been carried out for the currently available U28+ intensities of 2·1010 extracted particles per cycle, and the other calculation for the proposed FAIR booster operation with 1.5·1011 extracted particles per cycle. Results for both scenarios will be presented in this work.
GSI, Darmstadt
At GSI and for the FAIR project short heavy-ion bunches are required for the production and storage of exotic fragment beams as well as for plasma physics applications. In the SIS-18 and in the projected SIS-100 synchrotron longitudinal compression via fast bunch rotation is performed directly before extraction. In order to arrive at the required bunch length the rf cycle has to be optimized for high intensities to avoid the blowup of the occupied longitudinal phase space area. We will discuss experimental and simulation results of the rf capture at injection energy, the rebunching process at the final energy and the subsequent bunch rotation.