• M. Tobiyama, J.W. Flanagan, T.M. Mitsuhashi, T. Obina, M. Tadano, R. Takai
  KEK, Ibaraki

A transverse bunch by bunch feedback system using iGp feedback processors has been tested at the KEK-PF. The system consists of a bunch position detection system using 1.5 GHz components of the beam (3 x fRF), iGp feedback signal processors, and a transverse feedback kicker with a high power amplifier. It shows sufficient performance to suppress instabilities completely up to a beam current of 450mA. Results of the mode analysis of the instabilities using the grow-damp function of the iGp are also shown.

• U. Rauch, P. Forck, P. Hülsmann, P. Kowina, P. Moritz
  GSI, Darmstadt

A precise tune determination is crucial for stable operation of GSI SIS-18 synchrotron especially for intense beam conditions. In order to avoid nearby resonances in the tune diagram the fractional part of coherent betatron motion needs to be measured with a resolution of 10^-3 also during ramping mode. This is achieved using a fast digital readout system for Beam Position Monitors (BPM). The broadband BPM signal is sampled with a rate of 125 MSa/s which corresponds to an average of about 50 Sa per bunch for SIS-18 machine parameters. The signal is integrated bunch-by-bunch which minimizes thermal and digitization noise and the beam position is calculated. The tune is then determined in baseband directly by Fourier-transformation of the positions of a certain bunch typically over 2048 turns. This algorithm does not require any additional input parameter. Since particle losses due to significant emittance blow-up have to be avoided, excitation power has to be kept as low as possible. This was achieved using a digital pseudo random noise (PRN) generator for beam excitation, which produces white noise on a carrier frequency with adjustable bandwidth.