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Status of the SPS impedance model

Status of the SPS impedance model. C. Zannini, G. Rumolo, B. Salvant Acknowledgments: H. Bartosik , O.Berrig , G. Iadarola, E. M é tral , N. Mounet , V.G. Vaccaro, Jose E. Varela. Overview. Present SPS transverse impedance model Broadband impedance of step transitions

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Status of the SPS impedance model

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  1. Status of the SPS impedance model C. Zannini, G. Rumolo, B. Salvant Acknowledgments: H. Bartosik, O.Berrig, G. Iadarola, E. Métral, N. Mounet, V.G. Vaccaro, Jose E. Varela

  2. Overview • Present SPS transverse impedance model • Broadband impedance of step transitions • Future update of the model • SPS Longitudinal impedance model • Summary

  3. Present SPS transverse impedance model • Elements included in the database: • Realistic model that takes into account the different SPS vacuum chambers weighted by the respective length and beta function. Also the iron in the magnet is taken into account • 19 kickers (CST 3D simulation) • 106 BPHs (CST 3D simulations) • 96 BPVs (CST 3D simulations) • 200 MHz cavities without couplers (CST 3D simulations) • 800 MHz cavities without couplers (CST 3D simulations) • Enamel flanges (CST 3D simulations) Enamel flanges BPV BPH TW 200MHz and 800MHz Beam pipe Kickers

  4. Evolution of the extraction kickers in the SPS

  5. SPS vertical impedance model

  6. SPS horizontalimpedance model

  7. Vertical coherent tune shift 20 % 40 % 60 % Measurements performed in September 2012 80 % 100 % Present SPS impedance model reproduces about 70% of the vertical tune measured in the Q20 Present impedance model reproduces the instability behavior (H. Bartosik, Talk at the SPSU, 12 December 2013)

  8. Stability diagram: Q20 • Two regimes of instability in measurements • Fast instability threshold with linear dependence on εl • Slow instability for intermediate intensity and low εl • Excellent qualitative agreement with HEADTAIL simulations • Slightly lower threshold in simulation (amplitude detuning or space charge?) H. Bartosik measurements HEADTAIL simulations nominal Island of slow instability 4.5x1011p/b @ 0.35 eVs LIU SPS-BD, 12. December 2013

  9. Intra-bunch motion: Q20 (I) • Example for slow instability • Clear indication for mode 1 in measurement • Good agreement with HEADTAIL simulation H. Bartosik measurements HEADTAIL simulations LIU SPS-BD, 12. December 2013

  10. Intra-bunch motion: Q20 (II) H. Bartosik • Example for fast TMC instability • Excellent agreement between measurements and simulation • Travelling wave pattern clearly visible measurements HEADTAIL simulations LIU SPS-BD, 12. December 2013

  11. Horizontal coherent tune shift Measurements performed in February 2013 The kicker impedance model predicts a negative horizontal effective impedance (positive slope of the coherent tune shift) in agreement with the measurements

  12. Overview • Present SPS transverse impedance model • Broadband impedance of step transitions • Future update of the model • SPS Longitudinal impedance model • Summary

  13. Broadband impedance of a step transition • Based on the results of 3D EM simulations, the broadband impedance contribution due to an abrupt transition is independent of the relativistic beta. Therefore, based on the aperture model, the generalized broadband impedance of the PSB transitions has been calculated as: Transverse Impedance C. Zannini, Electromagnetic simulations of CERN accelerator components and experimental applications. PhD thesis, Lausanne, EPFL, 2013. CERN-THESIS-2013-076.

  14. Broadband impedance of step transitions L Weak dependence on L

  15. Broadband impedance of step transitions L2 Weak dependence on L2

  16. Broadband impedance of step transitions The imaginary part of the transverse impedanceisweaklydependent on the cavitylengthbelow 1 GHz For all the SPS cavitylikestructures the first resonating mode iswellabove 1 GHz (r<80 mm) L2 mm

  17. Broadband impedance of step transitions L2

  18. Broadband impedance of step transitions Courtesy of Jose E. Varela

  19. Vertical coherent tune shift 20 % 40 % 60 % 80 % 100 % Step transitions seem to explain almost the totality of the missed tune shift

  20. Pumping ports Impedance reduction campaign: shielding of the pumping ports, lepton cavities etc.) 2000 SPS Pumping port SPS Pumping port shielding

  21. Estimation of the broadband impedance of unshielded transitions between bending magnets and straight sections • 744 step transitions: • 377 MBA-Straight A • 377 MBB-Straight B Imag [ Zy(f=0) ]= 11.8 MΩ/m

  22. Overview • Present SPS transverse impedance model • Broadband impedance of step transitions • Future update of the model • SPS Longitudinal impedance model • Summary

  23. New elements to be added in the model • Simulations are ongoing or must be finalized • Septa • Wire scanner • Non standard elements (special transitions, valves) • Update due to future installations • New wire scanner • New kicker for high bandwidth feedback system • New MSI-V septum

  24. Overview • Present SPS transverse impedance model • Broadband impedance of step transitions • Future update of the model • SPS Longitudinal impedance model • Summary

  25. Status of the SPS longitudinal impedance model • Elements included in the database: • Realistic model that takes into account the different SPS vacuum chambers weighted by the respective length and beta function. Also the iron in the magnet is taken into account • 19 kickers (CST 3D simulation) Wall impedance Kickers

  26. Longitudinal wall impedance Calculation performed with ImpedanceWake2D

  27. Longitudinal impedance

  28. SPS impedance in total • + cavity & kicker impedance BPMs Courtesy H. Timko 200 MHz HOM Flanges Zs (?) LIU-SPS BD Meeting, 24th October 2013

  29. Overview • Present SPS transverse impedance model • Broadband impedance of step transitions • Future update of the model • SPS Longitudinal impedance model • Summary

  30. Summary and next steps • The SPS impedance model (kicker, wall, cavities, BPMs) explains about 70% of the measured vertical coherent tune shift • Transition pieces seem to be able to explainthe remaining 30% • More realistic model of transition pieces • Update of the model including septa and wire scanner • Continuously update of the model according to new installations and modifications

  31. Thank you for your attention

  32. Realistic models: SPS extraction kicker (MKE-L) Serigraphy Seven out of eight SPS extraction kickers have been serigraphed F. Caspers, T. Kroyer, M. Barnes, E. Gaxiola et al.

  33. Realistic models: MKE kicker with serigraphy

  34. Comparing MKE with and without serigraphy f=44 MHz

  35. Comparing MKE with and without serigraphy The peak observed in the MKE with serigraphy is a quarter-wavelength resonance on the finger length

  36. Evolution of the extraction kickers in the SPS: vertical tune shift Kickers play a major role in the SPS total impedance The trend of the vertical effective impedance along the last 10 years is in good agreement with the expected changing of the kicker impedance model

  37. Evolution of the extraction kickers in the SPS: horizontal tune shift Kickers play a major role in the SPS total impedance The trend of the horizontal effective impedance along the last 10 years is in good agreement with the expected changing of the kicker impedance model

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