Characterization of resonant impedances of CERN-SPS gate valves

For the CERN High Luminosity LHC project, a doubling of bunch intensity is foreseen. However, this intensity increase is currently limited by the LHC injector chain, in part due to longitudinal multi-bunch instabilities in the SPS. Therefore, the implementation of an accurate SPS impedance model was started some time ago in order to obtain a better understanding of instability sources and develop mitigation measures. In this paper, we present the electromagnetic characterization of commonly used all-metal gate valves with respect to their contribution to the SPS longitudinal impedance. The valve impedance was evaluated with commercially available EM-field simulation programs and verified with RF-bench measurements. Using this input, it was possible to obtain in particle simulations the dependence of the multibunch stability threshold on the number of these valves. The threshold can be increased by using commercially available impedance shielded valves. Consequently, we present the associated reduction in beam coupling impedance and the expected gain in beam stability if all existing unshielded valves are replaced by shielded ones.