Rabusov, Dmitrii (2023)
Characterization and minimization of the half-integer stop band with space charge in hadron synchrotrons.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00023222
Dissertation, Erstveröffentlichung, Verlagsversion

Kurzbeschreibung (Abstract)

This work characterizes the half-integer stop band for various beam distributions in hadron synchrotrons using simulation models with self-consistent space charge and experimental data. Synchrotrons for hadron beams are an important tool in fundamental research (particle and nuclear physics) and applied sciences (medical technology, materials science, industry). However, they are subject to undesirable effects, which degrade the quality of the beam. In any hadron synchrotron, the half-integer resonance is among the strongest effects that limit the maximum achievable beam intensity. The heavy-ion superconducting synchrotron SIS100, currently under construction at GSI, together with the already operating SIS18 synchrotron at GSI, should provide intense beams for future FAIR experiments. Using SIS100 as an example, this work develops a quantitative framework for characterizing the half-integer stop band for realistic, Gaussian-like distributed bunched beams in simulations. The developed framework is tested in a dedicated experiment in SIS18. In any synchrotron, gradient errors in quadrupole magnets induce the half-integer resonance. Due to the half-integer resonance, the beam intensity is limited, which is often referred to as the space-charge limit. To minimize the half-integer stop band for a bunched beam, and hence increase the maximum achievable intensity, lattice corrections are applied. Including space charge in the optimization procedure yields results equivalent to a conventional lattice correction. We validate in long-term simulations, that conventional correction tools are sufficient for increasing the gradient-error-induced space-charge limit of synchrotrons. This study identifies the tune areas affected by the half-integer resonance for varying space-charge strengths. The role of synchrotron motion in providing continuous emittance growth across the bunch is investigated. A key insight of this analysis is that, for bunched beams, a relatively small gradient error can result in a large half-integer stop-band width. The maximum achievable bunch intensity is thus reduced significantly. This contrasts with the findings in existing studies in literature based on more simplified beam distributions, where the space-charge limit does not depend on the strength of gradient errors. The reason for the discrepancy is identified in the increasing stop-band width for Gaussian distributions when space charge becomes stronger, which appears on time scales relevant for synchrotrons.

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