Characterization of longitudinal impedances in storage rings via multibunch effects - art. no. 112801

In this paper we present two new techniques for frequency- resolved charact erization of longitudinal impedances in storage rings. The first method is based on transient measurements of the growth rates and tune shifts of unst able coupled- bunch modes. In the second approach, estimates of the impedan ces are obtained from analysis of the steady- state synchronous phases of t he bunches for uneven fill patterns. These techniques are applicable to mea surements of both fundamental and higher- order mode (HOM) impedances and a llow characterization of shunt impedances and quality factors of the HOMs. Methods presented here are complementary to laboratory bench measurements o f rf cavities, in that the beam-based measurements directly sense the physi cal impedance in the installed configuration. Experimental results from the Advanced Light Source and BESSY- II are presented showing the use of these techniques to measure complex impedances.