GSI, Darmstadt
TEMF, TU Darmstadt, Darmstadt
To achieve a high current operation close to space charge limit, a precise tune measurement during a full accelerating cycle is required. A tune measurement system was recently commissioned at GSI SIS-18, which allows calculation of tune using digital position data. It consists of three distinct parts; an exciter which provides band limited white noise to excite coherent betatron oscillations in the beam. The fast ADCs digitize the BPM signals at 125MSa/s and the post processing electronics integrate the data bunch by bunch to acquire one position value per bunch. Subsequently base band tune is determined by frequency transformation of the position data. Using this system, the charge effects were studied by correlating the current levels to tune spread/shift in the GSI synchrotron SIS-18. The experiment was conducted at injection energy of 11.6 Mev/nucleon using U73+.
GSI, Darmstadt
TEMF, TU Darmstadt, Darmstadt
A study of the transverse dynamics of coasting ion beams with moderate space charge is presented. An analytic model based on the dispersion relation with a linear space-charge force is used to describe the impact of space charge on transverse beam transfer functions (BTFs) and the stability limits of a beam. The dielectric function obtained in this way is employed to describe the transverse Schottky spectrum with linear space charge as well. The difference between space charge and impedance effects is highlighted. An experiment performed in the heavy ion synchrotron SIS-18 at GSI to detect space-charge effects at different beam intensities is explicated. The measured transverse Schottky spectra, BTFs and stability diagrams are compared with the analytic model. The space-charge parameters evaluated from the Schottky and BTF measurements are compared with estimations based on measured beam parameters. Furthermore, particle tracking simulations demonstrating the impact of collective effects on the Schottky and BTF diagnostics are presented. The simulation results are used to verify the space-charge model.
