SPS Wideband Transverse Feedback Kicker: Design Report

The SPS wideband transverse feedback system is being developed to control vertical beam instabilities arising from intensity dependent effects like electron cloud instability (ECI) and the transverse mode coupling instability (TMCI). As part of the LHC Injector Upgrade (LIU) project, a wideband kicker is necessary as a damper to control unstable modes within a bunch. Several types of kicker structures, including cavities, striplines, and slotted structures have been studied to evaluate the operating bandwidth, transverse shunt impedance, and beam coupling impedance. Studies and results from all structures are described below, including three potential paths to implement these structures as a wideband kicker system. A single, slotted-coaxial kicker of 1 m length provides substantial kick strength (integrated transverse voltage) over a bandwidth ranging from nearly DC to 1 GHz. An array of four 10 cm long striplines provides substantial kick strength from DC to 750 MHz. For a given amplifier power of 500 W, the array of striplines can provide twice the transverse detecting voltage as the slotted kicker for frequencies up to 200 MHz. At frequencies 800 - 1000 MHz the transverse voltage generated by the slotted kicker dominates that of the stripline array. We recommend to CERN that both the slotted-coaxial kicker and the array of striplines should undergo more detailed mechanical design and be built as prototype wideband kickers for installation in the SPS.