1. LHC First LHC Emittance Measurements at 6.5 TeV Emittance Meeting August 26, 2015 Maria Kuhn – August 26, 2015 Many thanks to G. Baud, E. Bravin, B. Dehning, J. Emery, A. Guerrero, V. Kain, A. Langner, Y. Papaphilippou, E. Piselli, R. Tomas, G. Trad, and J. Wenninger,...

2. LHC Outline oAccuracy of LHC emittance measurements with wire scanners − Wire scanner calibration Orbit bumps Photomultiplier saturation studies Major constraints: wire scanner intensity limits oLHC optics measurements oEmittance growth during the LHC cycle − Injection plateau and IBS − Ramp to 6.5 TeV −  * squeeze − BSRT measurements − Comparison with emittance from luminosity 2 M. Kuhn - 14/08/2015

3. LHC LHC WIRE SCANNER CALIBRATION 3 M. Kuhn - 14/08/2015

4. LHC Orbit Bump Calibration (1) oUsing local orbit bumps to verify the wire position measurement calibration of the wire scanners − Orbit measured with BPMs and extrapolated to wire scanner − Not energy dependent − 2015 results comparable to 2012 calibration results − If reproducible should change calibration factor in front-end − Also important for BSRT cross calibration  overestimating B2V emittances by ~ 6 % 4 M. Kuhn - 14/08/2015 B2V1 ~ slope difference + 3 %

5. LHC Orbit Bump Calibration (2) oSummary of results: oMostly emittances are overestimated by LHC wire scanners − Exception: B1V2 oBest would be to correct the calibration factor on the front-end − Would need another measurement to check reproducibility of results 5 M. Kuhn - 14/08/2015 Wire ScannerError on positionError on emittance B1H2 + 3.6 %+ 7.2 % B1V2 - 2.6 %- 5.2 % B2H1 + 4.5 %+ 9 % B2V1 + 3.3 %+ 6.6 %

6. LHC Photomultiplier Saturation Studies Run 1 oPhotomultiplier (PM) gain and filter can have a strong influence on measured beam size − See measurements of 2012 6 M. Kuhn - 14/08/2015 PM saturation studies at 4 TeV in 2012.PM saturation studies at 450 GeV in 2012. Observed strong gain dependence at 450 GeV and 4 TeV during Run 1!

7. LHC Photomultiplier Saturation Studies Run 2 oStudies at 450 GeV with 6 bunches of different emittances: − Systematically changing gain and filter of PMs − Example scanner B2V1, other planes look similar oStudies at 6.5 TeV more difficult – very small range of settings − Due to a lot of light at higher energies 7 M. Kuhn - 14/08/2015 6.5 TeV 450 GeV

8. LHC PM Saturation Studies @ 450 GeV oBeam sizes grow at 450 GeV. Effect needs to be removed: − Exponential fit of scans with reference settings to take out effect of growth at injection plateau 8 M. Kuhn - 14/08/2015

9. LHC PM Saturation Studies @ 450 GeV oBeam sizes grow at 450 GeV. Effect needs to be removed: − Exponential fit of scans with reference settings to take out effect of growth at injection plateau − Average beam sizes per PM setting (combination of filter and gain)  Beam size minus growth from exponential fit 9 M. Kuhn - 14/08/2015 No dependence on gain or filter at 450 GeV! Changes during LS1: One broken PM has been replaced and power supply schematics have been upgraded. Also reduced PM gain dependency on intensity.

10. LHC Résumé Wire Scanner Accuracy oPossibly “small” calibration error on position measurement  Hence beam size measurement error of about - 3 to + 5 % depending on scanner − Results in 5 - 10 % emittance measurement error oNo PM saturation effects with single bunches − PM saturation might have to be revisited for trains − Further investigations / verification of optimum working point in the laboratory foreseen oFairly large statistical fluctuations of scan-to-scan emittance measurements at high energy − Limited precision on wire position measurement results in 10 – 20 % beam size spread from scan to scan − Recipe: average emittance over 3 wire scans to get reliable measurement 10 M. Kuhn - 14/08/2015

11. LHC Wire Scanner Intensity Limits Limits so far: oMaximum 2.7 x 10 13 protons per beam at 450 GeV − Corresponds to ~ 240 nominal bunches oUp to now: maximum 2.3 x 10 11 protons per beam at 6.5 TeV − Corresponds to ~ 2 nominal bunches oNew Limit: maximum 1.6 x 10 12 protons per beam at 6.5 TeV − Corresponds to ~ 10 - 14 nominal bunches − To be implemented soon oRun 2: rely even more on an operational synchrotron light monitor (BSRT) 11 M. Kuhn - 14/08/2015

12. LHC OPTICS MEASUREMENTS 12 M. Kuhn - 14/08/2015

13. LHC LHC Optics Measurements oCan use results from optics measurements with the turn-by-turn phase advance method and k-modulation for: oOutstanding measurements: − K-modulation at 6.5 TeV and after the squeeze − Turn-by-turn phase advance measurements at 450 GeV (repeated) and during the ramp! oFor emittance plots: using measured  where possible −  function measurement error < 3 % − Maximum measured beta beat is 5 % at the wire scanners − Linear interpolation during the ramp and squeeze 13 M. Kuhn - 14/08/2015 IR4IP1/2/5/8 InjectionRampFlattopAfter Squeeze ** K-modulation xx Turn-by-turn xx

14. LHC Motivation: More K-Modulation Measurements Comparison of optics measurements with k-modulation and turn-by-turn phase advance method: − Consistent results − Small errors with k-modulation 14 M. Kuhn - 14/08/2015 Want precision emittance measurements; Need most accurate optics measurements. A. Langner

15. LHC  * Measurements oSinusoidal k-modulation in IP1/5 on August 8, 2015 15 M. Kuhn - 14/08/2015 I = 10 A f = 0.01 Hz Measurement error on tune oscillation amplitude in sub- percent level   * meas. uncertainty ≤ 1 %  Beta beat ≤ 1 %  Compatible with turn-by-turn measurements Prelim inary! IP1 [m]IP5 [m] B1B2B1B2  * H 0.810.790.80  H 0.010.0040.0010.01  * V 0.810.79  V 0.01 0.002

16. LHC EMITTANCE GROWTH DURING THE CYCLE 16 M. Kuhn - 14/08/2015

17. LHC squeeze Emittance Evolution during the Cycle oFill 3954 (July 4, 2015) 17 M. Kuhn - 14/08/2015 Partly unphysical emittance evolution! From Run 1 experience: optics

18. LHC Emittance Growth in Numbers: Fill 3954 oAverage emittance of 4 scans oSPS emittance at extraction: H = 2.16  m, V = 2.0  m oAdding additional (pessimistic) 10 % uncertainty on wire scanner position measurement − Result from orbit bump calibration  Measurement error larger than measured emittance growth! 18 M. Kuhn - 14/08/2015 Fill 3954, Bunch 1InjectionCollision  [  m]  [  ] B1H  [  m] 2.66 ± 0.142.95 ± 0.160.29 ± 0.2111 ± 18 B1V  [  m] 2.40 ± 0.112.80 ± 0.130.40 ± 0.1717 ± 17 B2H  [  m] 2.12 ± 0.082.14 ± 0.180.02 ± 0.201 ± 19 B2V  [  m] 2.85 ± 0.073.14 ± 0.320.29 ± 0.3210 ± 21

19. LHC Emittance Growth vs. IBS oIBS simulations with MADX IBS module − Including: dispersion, radiation effects, measured bunch length through cycle, measured initial intensity and emittance 19 B1H grows more strongly than IBS suggests. Origin of growth in B1V? IBS could fit evolution in B2H. Need optics through the ramp for B2V.

20. LHC Cycle: Results Reproducible? 20 M. Kuhn - 14/08/2015 squeeze Emittance evolution looks different for this fill. ‘Shrinking’ emittances during ramp also in beam 1. Large error bars in beam 2. oFill 4186 (August 9, 2015) – wire scanner measurements during ramp (start at 1 TeV) and squeeze

21. LHC 450 GeV: Results Reproducible? 21 M. Kuhn - 14/08/2015 Bunch 2: Horizontal planes grow ~ 0.1  m in 20 min. No blow-up in the vertical planes. oFill 4186 (August 9, 2015) – BSRT measurements at 450 GeV − LHC fully commissioned now Absolute growth   BSRT not calibrated yet Each point: average of several 100 measurements

22. LHC Ramp: Average Emittance Growth oTo better visualize the average growth overlaying all ramps 22 M. Kuhn - 14/08/2015 B1H: ~ 0.1  m blow-up, reproducible fluctuation during the ramp. B1V and B2H no blow-up. B2V: ~ 0.1  m blow-up, large error bars from in-out- scan deviations.

23. LHC Squeeze: Emittances Preserved ? oBSRT measurement during the  * squeeze from 11 m to 80 cm 23 M. Kuhn - 14/08/2015 Large error bars in B1H. Very small growth in B1V ~ 0.1  m. Tune change

24. LHC Squeeze: Results Reproducible? oBSRT and wire scanner measurement during the  * squeeze from 11 m to 80 cm 24 M. Kuhn - 14/08/2015 Good agreement between wire scanner and BSRT results.

25. LHC Collisions: Emittance from Luminosity oComparison of emittance from wire scans and luminosity − Fill 3954, one bunch in collision − Average of 4 measurements with similar timestamps − According to experts ATLAS/CMS luminosity low by ~10 %, assume error on luminosity ±10 % 5 % error on (nominal) crossing angle and ±1 cm error on measured bunch length should be added oPreliminary: ATLAS and wire scanner results agree within errors! − Better than during Run 1 25 M. Kuhn - 14/08/2015 Fill 3954, Bunch 1InjectionCollisionGrowth WS  [  m] 2.51 ± 0.102.75 ± 0.200.2410 % ATLAS  [  m] 2.97 ± 0.360.4619 % CMS  [  m] 4.01 ± 0.471.564 %

26. LHC Comparison SPS – LHC - Luminosity oSo far only looked at low intensity beams with 2 bunches oNOW: physics beams with more bunches (50 ns and 25 ns trains) − Convoluted emittance (H + V) of SPS wire scans at 450 GeV − Emittance per plane of LHC wire scans at 450 GeV (lacking scans!) − Convoluted emittance from ATLAS and CMS luminosity 26 M. Kuhn - 14/08/2015 Results seem to indicate less growth through the cycle than in 2012. Total emittance blow-up during the cycle seems to be independent of #bunches. Last collision s for physics: July 20!

27. LHC oOverall average transverse normalized emittance blow-up through the LHC cycle: − ~ 0.4 – 0.9  m from injection into the LHC to start of collision (convoluted  ) for the first injected batch of 144 bunches per beam Reminder: 2012 Emittance Blow-up 27 M. Kuhn - 14/08/2015

28. LHC Summary oGood progress with understanding the wire scanner (and BSRT) emittance measurements − In general seem to be in a better shape than during Run 1 − More optics measurements are required, especially during the ramp oFor some fills the emittances seem to be growing in all planes through the cycle and mainly during injection plateau and ramp − Origins: IBS, … what else? oWith the still not fully calibrated luminosity data: better agreement between wire scans and emittance from ATLAS luminosity oLuminosity measurements (ATLAS) over the last weeks indicate small growth through the cycle 28 M. Kuhn - 14/08/2015

29. LHC To Do oOptics measurements in point 4 − Repeat turn-by-turn phase advance measurements at 450 GeV − Turn-by-turn phase advance measurements during the ramp! − K-modulation at 6.5 TeV and after the squeeze oRepeat orbit bump scans – to check reproducibility oUnderstand additional sources of growth – if there are any − Measure once more during the entire cycle with wire scanners − Possible also compare to LHCb SMOG data and Van der Meer scans (bunch emittance measurements in all planes during collisions) oMore wire scans at injection in all planes during physics filling Thank you for your attention! 29 M. Kuhn - 14/08/2015

30. LHC APPENDIX 30 M. Kuhn - 14/08/2015

31. LHC Bunch Length Measurement oLongitudinal bunch shape not Gaussian at 6.5 TeV − Due to controlled longitudinal RF blow-up at flattop energy oBut LHC bunch length monitor publishes 4  bunch length values based on FWHM algorithm assuming Gaussian profiles  Bunch length error ±1 cm!  “True” emittance from luminosity should be larger by 0.1  m 31 M. Kuhn - 14/08/2015

32. LHC Motivation: More K-Modulation Measurements oRecent k-modulation measurement in the LHC (23. July) − IP1 at 3 m  * − Pilot bunch without tune chirp 32 M. Kuhn - 14/08/2015 Very promising results, measurement error on tune oscillation in sub- percent level!