Two different tune measurement systems have been installed in the GSIheavy-ion synchrotron SIS-18. Tune spectra are obtained with high accuracyusing these fast and sensitive systems. Besides the machine tune, the spectracontain information about the intensity dependent coherent tune shift and theincoherent space charge tune shift. The space charge tune shift is derived froma fit of the observed shifted positions of the synchrotron satellites to ananalytic expression for the head-tail eigenmodes with space charge.Furthermore, the chromaticity is extracted from the measured head-tail modestructure. The results of the measurements provide experimental evidence of theimportance of space charge effects and head-tail modes for the interpretationof transverse beam signals at high intensity.
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