2. Chromaticity dependence of the vertical effective impedance in the PS Chromaticity dependence of the vertical effective impedance in the PS S. Persichelli N. Biancacci, M. Migliorati, B. Salvant, G. Sterbini, S. Gilardoni, E. Metral, N. Wang MSWG meeting 19-06-2015

3. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

4. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

5. PS impedance model  Includes contribution of:  Indirect space charge  Resistive wall  Kickers  Cavities  Vacuum (flanges, valves, pumps, bellows)  Wire scanner  Elements installed in LS1 (dummy septum, longitudinal damper, stripline pickup)  All the impedances are weighted by the β function of the PS lattice  Impedance model computed at different energies (1.4, 2, 7, 13, 25 GeV) (Nicolo’)  Access at /afs/cern.ch/project/impedance/PS_impedance_database  PS Impedance webpage: http://impedance.web.cern.ch/impedance/ 5

6. Total impedance model (2 GeV) Effective transverse impedance is defined as the impedance weighted by the transverse bunch power spectrum! 6

7. Total impedance model (25 GeV) 7

8. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

9. How do we measure the transverse impedance The impedance is always considered total! 9

10. Tune measurements in the PS Coherent betatron tune: the number of betatron oscillations per turn of the bunch center of mass Coherent betatron tune: the number of betatron oscillations per turn of the bunch center of mass Chirp signal is used to kick the beam (single bunch) Chirp signal is used to kick the beam (single bunch) The transverse position of the bunch centroid is acquired every turn by a BPM A diode detector converts the modulation of the BPM pulses, related to beam oscillations, into a signal (AF range). FFT 10

11. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

12. Measurements of the transverse impedance (2012) Aim of 2012 tune shift measurement: assess the effective impedance budget at injection and extraction energy 12

13. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

14.  Tune shift measurements revealed an decrease of vertical impedance of 2 MΩ/m from 2012  No major changing for the impedance budget after LS1  We run few tests to try to repoduce this measurement  Change of excitation (chirp, kick)  Variation of bunch length  Orbit correction  Last test: try to measure the tune shift with different vertical chromaticity set on the machine working point Tune shift measurements at 25 GeV (2014) 2/9/2014 3/9/2014 14

15. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

16. Working point and chromaticity in the PS 16

17. Measurements of the transverse impedance (2014) at different energies with chromaticity  3 energies considered  For each energy, the impedance corresponding to different chromaticities is computed from tune shift measurement.  The impedance is increasing with chromaticity! 17

18. Measurements of the transverse impedance (2014) at zero chromaticity 25 GeV 7 GeV 13 GeV 18

19. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

20. Tune shift measurement at 2GeV (2014)  Measurement at 2 GeV revealed the same increasing trend with chromaticity  The tune measurement has not a good quality has for the other energies considered  The zero chromaticity value does not correspond to the value predicted by the model!   Need to repeat the measurement in 2015! 20

21.  Measurement at 2 GeV starting from March 2015.  Large spread between tunes acquired at the same intensity.  Machine strongly coupled on the two planes.  Tune signal not symmetric respect with the direction of chirp excitation: the impedance calculated from tune shift is different if we excite the tune in the range 0.2-0.3 or 0.7-0.8.  The impedance vs chromaticity trend of 2014 can’t be reproduced.  Impedance calculated from tune shift at different chromaticities are different every day. Issues with tune shift measurement at 2 GeV (2015) The measurement at 2 GeV is affected by the contribution of an “hidden player” of the machine that does not allow to measure the right tune! 21

22. Chirp excitation range  Tune signal not symmetric respect with the direction of chirp excitation. The impedance calculated from tune shift is different if we excite the tune in the range 0.2-0.3 or 0.7-0.8 22

23. Improvements of the tune shift measurement technique at 2GeV (2015) TOF LHC INDIV 23

24. Effect on machine linear coupling Current set on the skeq quadrupoles: +0.35 A – 0.35 A Current set on the skeq quadrupoles (optimum): +0.39 A – 0.39 A Fully coupled machine: -0.30 A + 0.30 A 24

25. Tune shift measurement at 2GeV (2015) with LCH_INDIV beam and no coupling  Measurement at 2 GeV revealed the increasing trend with chromaticity  The tune measurement has a good quality!  The zero chromaticity impedance correspond to the value predicted by the model for the 4 energies considered! 25

26. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

27. 25 GeV 7 GeV 13 GeV 2 GeV Summary at zero chromaticity 27

28. Comparison between impedance model and effective impedance at zero chromaticity  Measurement and simulation are in excellent agreements (almost 100%) at 2 and 25 GeV!  At 7 and 13 GeV measurement and simulation are in very good agreement (70-80%)  Coupling is decreasing with the beam energy: measurement at 7 GeV were probably affected! The transverse impedance model of the PS is fully validated by simulation and beam based measurement! 28

29. The indirect space charge contribution 2 GeV 7 GeV 13 GeV 25 GeV 29

30. Agenda  Overview of the PS impedance model  How to measure the effective impedance in the PS  Tune shift measurement in 2012 at 1.4 and 25 GeV  Tune shift measurement in 2014 at 25 GeV  Impedance vs chromaticity measurement in 2014  Tune shift measurement in 2014-2015 at 2 GeV  Impedance model validation with measurement  Conclusions

31. Conclusions The imaginary part of the vertical effective impedance of the PS has been computed measuring the tune shift with intensity at different energies and zero chromaticity. The transverse impedance model of the PS has been validated at four different energies with simulations and analytical methods. The computed and the measured impedance model are in excellent agreement. Tune shift measurement revealed that the impedance increases with chromaticity for all the energies considered. The tune measurement is very sensitive to machine coupling, especially at low energies. Tune measurements are reproducible working with a not coupled machine and a LHC INDIV beam from the PSB

32. Publications Journals and proceedings :  M. Migliorati, S. Persichelli et al., Beam-wall interaction in the CERN Proton Synchrotron for the LHC upgrade, Phys. Rev. ST Accel. Beams 16, 031001, 2013.  S. Persichelli, Trapped modes in a dummy extraction septum for CERN Proton Synchrotron, Il Nuovo Cimento Vol. 37 C, N. 4, July 2014.  N. Biancacci, S. Persichelli et al., Beam Coupling Impedance Localizing Technique Validation and Measurements in CERN Machines, Proc. of IPAC13, 2013.  S. Persichelli et al., The Proton Synchrotron Transverse impedance model, Proc. of IPAC14, 2014.  S. Persichelli et al., Impedance Studies of the Dummy Septum for CERN PS Multi- turn Extraction, Proc. of IPAC14, 2014.  S. Persichelli, M. Migliorati et al, Impedance Studies for the PS Finemet Loaded Longitudinal Damper, Proc. of IPAC14, 2014.  S. Persichelli, M. Migliorati, Beam coupling impedance simulation and RF measurements of a passive extraction septum for particle absorbing in the CERN proton synchrotron, Atti della XX RiNEm 2014.  S. Persichelli, N. Biancacci et al., Chromaticity Dependence of the Transverse Effectivie Impedance in the CERN Proton Synchrotron, Proc. of IPAC15, 2015.  H. Damerau, M. Migliorati, S. Persichelli et al., Evaluation of the broadband longitudinal impedance of the CERN PS, CERN-ATS-Note-2012-064 MD, 2012.  S. Persichelli, M. Paoluzzi et al., Finemet cavity impedance studies, CERN-ACC- NOTE-2013-0033, 2013.

34. How to build an impedance model Get to know the machine elements: Shape of the beam pipe Cavities for acceleration Magnets Beam instrumentations… Get to know the machine elements: Shape of the beam pipe Cavities for acceleration Magnets Beam instrumentations… Perform beam based measurements of the global machine impedance Perform beam based measurements of the global machine impedance Perform simulations/ calculation/ measurements of the impedance contributors Sum of the contributions to obtain the total impedance The impedance model is built YES NO Are they in agreement? ! !

35. Total impedance model (2 GeV)

37. Total impedance model (25 GeV)