Abstract
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.
Highlights
The upgrade of the CERN Super Proton Synchrotron (SPS) for the high luminosity LHC project (HL-LHC) requires a significant improvement in longitudinal beam coupling impedance to allow operation at the desired bunch intensities
After accounting for the general SPS impedance reduction foreseen in LS2, the SPS all-metal sector valves were identified to reduce the multi-bunch instability threshold significantly
This translates to an intensity limitation lower the required 2.4 × 1011 p/b at a 4σ bunch length of 1.65 ns for the High Luminosity LHC project
Summary
The upgrade of the CERN Super Proton Synchrotron (SPS) for the high luminosity LHC project (HL-LHC) requires a significant improvement in longitudinal beam coupling impedance to allow operation at the desired bunch intensities. For the EM-evaluation of these sector valves, the CAD model was imported into the EM-simulation programs for calculation of eigenmodes (HFSS [4] and CST [5]), Sparameter transmission (CST) in frequency domain to benchmark the RF-measurements and wakefields (CST) for coupling impedance calculation in time domain.
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