DA-PHI-NE ACCUMULATOR RING COUPLING IMPEDANCE MEASUREMENTS

We discuss the results of the bunch lengthening and synchronous phase shift measurements performed during the commissioning of the DA Phi NE accumulator ring and aimed to estimate the machine longitudinal coupl ing impedance. The dependence of the bunch length on the average curre nt measured experimentally is in a good agreement with that predicted numerically. The low frequency machine impedance is estimated to be 3. 55 Omega. It was also found that the parasitic beam power losses and t he bunch shape distortion depend strongly on the actual RF cavity High er Order Mode (HOM) positions with respect to the beam power spectrum lines. In particular, we observed that the effect of the HOMs can be m inimized by raising the cavity temperature to 37 degrees C. (C) 1998 E lsevier Science B.V. All rights reserved.