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SPS impedance reduction: discussion

SPS impedance reduction: discussion. LIU-SPS BD WG meeting 24.10.2013. SPS longitudinal impedance budget. Refs. G. Dome, B. Salvant, K. Zannini, J. Varela, F. Caspers, T. Argyropoulos, H. Timko. MKP – next largest kicker impedance. After shielding of MKEs

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SPS impedance reduction: discussion

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  1. SPS impedance reduction:discussion LIU-SPS BD WG meeting 24.10.2013

  2. SPS longitudinal impedance budget Refs. G. Dome, B. Salvant, K. Zannini, J. Varela, F. Caspers, T. Argyropoulos, H. Timko

  3. MKP – next largest kicker impedance After shielding of MKEs the MKPs have now the highest contribution to the total SPS broad-band impedance (< 2 GHz) C. Zannini data (plot H.Timko)

  4. Longitudinal instabilities in the SPS • Longitudinal instabilities limit the performance of the LHC beam in the SPS • More 200 MHz voltage is required in future (HL-LHC) due to longitudinal emittance blow-up needed for beam stability • Coupled-bunch instability threshold during ramp (energy) scales with total current (comparison 25ns<->50ns); instability of one batch is similar to 2,3 or 4 batches, but final emittance also increases ~ Nb 25 nsbeam: Nb=1.35x1011 -> 0.47 eVs 50 ns beam: Nb=1.6x1011 -> 0.46 eVs • 2012 measurements with single high intensity bunches show strongbunch lengthening @450GeV in Q20 and Q26 (800 MHz on) during LHC and AWAKE MDs • Most probably we see effect of different impedances: • “broad-band” responsible for single bunch (mw) instability • “narrow-band” responsible for bunch coupling: 50 ns < Q/(pi fr) < 225 ns => 150 < Q/fr[GHz] < 700 => for fr=2 GHz: 300 < Q < 1400

  5. SPS impedance reduction • For HL-LHC beams the longitudinal emittance blow-up during cycle could be a serious problem even after the 200 MHz RF upgrade. • At the moment it is assumed that due to impedance effects, at 450 GeV/c required V ~ Nbunch • We need to consider impedance reduction program, but first all important impedance sources should be identified => continue work on impedance calculations and measurements

  6. Next steps • Need to have reliable SPS impedance model (Rshand Q): kickers (ZS, MKP), BPMs, vacuum chamber cross-section variations, HOMs of 200 MHz and 800 MHz RF systems • Need to reproduce in simulations all single bunch measurements: • Long bunches RF off @26 GeV/c • Synchrotron frequency shift with intensity @26 GeV/c • Instability with RF on @26 GeV/c • Emittance blow-up during ramp and flat top • Simulation of multi-bunch effects (BPMs?)

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