Design and commissioning of third harmonic cavities at BESSY II

We report on the design and commissioning of passive third ham-ionic caviti es that have been installed in BESSY-II, a third generation high brightness synchrotron light source, Four cavities were installed to lengthen the ele ctron bunches and increase the beam lifetime which is dominated by large an gle intrabeam (Touschek) scattering. During routine user operation the syst em is running stable in a low power mode resulting in a current dependent b unch lengthening of up to a factor of 1.4, resulting in a significant impro vement of beam lifetime. We also observed longitudinal stabilization of the beam using the cavities without the use of longitudinal feedback. (C) 2001 Elsevier Science B.V. All rights reserved.