Longitudinal instability thresholds on the SPS flat top LIU-SPS Beam Dynamics Working Group J. Repond, A. Lasheen, E. Shaposhnikova Beams Department - Radio-Frequency Group - Beams & RF Studies, CERN April 21, 2016 LIU-SPS BDWG Longitudinal instability thresholds on the SPS flat top April 21, 2016 1 / 27
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Longitudinal instability thresholds on the SPS flat topLIU-SPS Beam Dynamics Working Group
J. Repond, A. Lasheen, E. Shaposhnikova
Beams Department - Radio-Frequency Group - Beams & RF Studies, CERN
April 21, 2016
LIU-SPS BDWG Longitudinal instability thresholds on the SPS flat top April 21, 2016 1 / 27
Outline
1 Motivations
2 Impedance model
3 Instability thresholds
4 Missing impedance
5 How to reach HL-LHC goals ?
6 Conclusion
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Motivations
LIU-SPS BDWG Longitudinal instability thresholds on the SPS flat top April 21, 2016 3 / 27
Motivations
• The HL-LHC goals achieved with tight margins by impedance reduction ofvacuum flanges .
• Is there any other way to obtain the desired stability threshold ?
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Impedance model
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Impedance model
Current configuration• TWC200
- 2◊ 4 sections + 2◊ 5 sections.- 20dB reduction on main
harmonic to modelize feedback.- 7 MV assumed, independent of
beam current.
• - BPM - QD and BPM - QF.- QD type flanges.
• - QF type flanges.
• - 42 remaining unshieldedpumping ports.
Future configuration• TWC200
- 4◊ 3 sections + 2◊ 4 sections.- 20dB reduction on main
harmonic to modelize feedback.- 10 MV assumed, independent of
beam current.+ 3 sections
- Main harmonic estimated usingG. Dôme (CERN-SPS/ARF/ 77-11,1977).
- HOMs reduced by 40% bycomparing 4 and 5 sections.
• - 0 impedance for the BPM - QF.• - QF reduced by a factor 20
assumed (J.Varela).• - 25 remaining unshielded
pumping ports.
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Impedance model
• Currentconfiguration
• Futureconfiguration
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Instability thresholds at450GeV for 72 bunches
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Instability thresholds at 450 GeV for 72 b, 2 RF
• Comparaison nowand after upgrade.
• TWC800 at 10%.
• HL-LHC intensitygoal included.
• Referencemeasurement.
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Instability threshold - Currentsituation
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