Sabrina Appel:
Simulation and measurements of longitudinal space charge effects for high intensity ion beams in the SIS18 synchrotron

TU Darmstadt 2011, written in German.


The results of the PhD thesis can be found also in
S. Appel, O. Boine-Frankenheim: Microbunch dynamics and multistream instability in a heavy-ion synchrotron, Phys. Rev. ST Accel. Beams 15, 054201 (2012)

The international research facility FAIR will be constructed to explore the evolution of the universe and the structure of matter. For the FAIR-project the existing accelerator facility GSI Helmholtz Center for Heavy Ion Research located at Darmstadt (Germany) will serve as injector. FAIR will provide high-energy ion beams with unprecedented intensity and quality for the research purposes. There will be also the possibility to explore the nature of matter with antiprotons. Therefore, the GSI facility must renew the existing linear accelerator UNILAC and the synchrotron SIS18.
To produce intense beams in SIS18 for example one have to take care of the beam quality. One part is the longitudinal beam quality after the injection. To accelerate intense beams in the SIS18 as many ions as possible must be within the longitudinal acceptance given by the high- frequency cavities. At low energies and high intensities the existing collective effects make it difficult to reach the required longitudinal beam quality - i. e. the momentum spread - for the injected coasting beam. Consequently, the longitudinal beam quality should be routinely measured directly after injection. With the Schottky-diagnostic it is possible to measure the momentum spread and revolution frequency.
After injection collective effects can cause the multistream instability induced by the space charge impedance. The multistream instability lead to persistent current fluctuations and an accompanying pseudo-Schottky spectrum. The coherent structure and the pseudo-Schottky spectrum lead to difficulties in measuring momentum spread and revolution frequency. Such coherent structures are observed on the Schottky-bands at intense beams in the SIS18.
Therefore, the aim of the research work is to understand the evolution of the longitudinal beam distribution along the transport line from the linear accelerator UNILAC to the SIS18 and in the SIS18 after the injection. Space charge effects cause an increase of the momentum spread. Hence, it is essential to have a qualitative and quantitative description of the space charge effects. For this reason this research work will occupy with the one-dimensional model of the longitudinal beam space charge field. In particular the proportionality factor geometry-factor (g-factor) will be discussed. The geometry-factor is an important parameter for describing space charge effects and their effects. Furthermore, this research work discuss the multistream instability theoretical described by I. Hofmann and its effect on the Pseudo-Schottky-spektrum. The effects of the injection process on the longitudinal beam quality in the SIS18 and on the multistream instability will also be discussed.