MEASUREMENTS OF THE COUPLING IMPEDANCE OF THE SNS EXTRACTION KICKERS.

The Spallation Neutron Source (SNS) Accumulator ring extraction system includes 14 modules of ferrite kicker magnets with window-frame geometry. Among all ring components, the extraction kickers make the single largest contribution to the coupling impedance budget. A prototype was constructed and various design options impacting the transverse coupling impedance have been thoroughly studied. Bench as well as system measurements were performed to determine the benefits from an external circuit resistance, from using different ferrites material, and from adding a novel ferrite winding. The results presented in this paper confirm that a resistive termination in the external circuit yields a solution with sufficiently reduced transverse coupling impedance. In order to determine the total contribution of all modules, an equivalent circuit and a simple scaling law was derived from measurements of full and half size magnets