• R. Singh, P. Forck, P. Kowina, P. Moritz, U. Rauch
  GSI, Darmstadt
• T. Weiland
  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⁺.