DAΦNE accumulator ring coupling impedance measurements

We discuss the results of the bunch lengthening and synchronous phase shift measurements performed during the commissioning of the DAΦNE accumulator ring and aimed to estimate the machine longitudinal coupling impedance. pendence of the bunch length on the average current measured experimentally is in a good agreement with that predicted numerically. The low frequency machine impedance is estimated to be 3.55 Ω. also found that the parasitic beam power losses and the bunch shape distortion depend strongly on the actual RF cavity Higher Order Mode (HOM) positions with respect to the beam power spectrum lines. In particular, we observed that the effect of the HOMs can be minimized by raising the cavity temperature to 37°C.