Novel cavity with ultra-low R/Q for CLIC damping ring RF system

The Compact Linear Collider (CLIC) Damping Rings (DRs) need to generate ultra-low emittance bunches to achieve high luminosity in CLIC. This requires many wiggler magnets with big energy loss which is compensated by the Radio Frequency (RF) system. The resulting strong beam loading transients affect the bunch position. At the same time, there is a very tight specification for the bunch position along the bunch train, to maintain the CLIC luminosity at the nominal level. These conflicting specifications lead to a challenging design for the RF system. In this work, a novel cavity with an ultra-low R/Q parameter of below 1 Ω is proposed to minimize the transient beam loading effects below acceptable level. The design strategy, the achieved parameters and resulting overall performance of the RF system including both the high power and Low-Level RF (LLRF) aspects are presented and discussed.