1. LHC Updates on the LHC Wire Scanner Application --- Transverse Emittance Blow-up during the LHC Ramp Verena Kain, Maria Kuhn 1 11/12/2013

2. LHC Outline PART 1 oUpdates on the LHC wire scanner application − Requirements from last meeting − First version of the new GUI − The new philosophy PART 2 oEmittance blow-up during the LHC ramp − Transverse emittance measurements in 2012 − Possible sources of emittance blow-up during the LHC ramp 2 11/12/2013

3. LHC PART 1: Updates on the LHC Wire Scanner Application 3 11/12/2013 oRequirements from last meeting oFirst version of the new GUI oThe new philosophy

4. LHC Requirements from Last Meeting (1) oCreate LSA parameter for nominal settings − Load to frontend with sequencer − Monitor on application oInjection sequencer sets circulating + next injected bunch pattern for each new injection oAutomatically use optics for resident beam process − Display used optics name − Use measured optics if available in DB for beam process oCan launch scans for all 4 scanners in one go − Application looks after scheduling Framework already provides possibility to work with several scanners Framework already provides possibility to work with several scanners 11/12/2013 4

5. LHC Requirements from Last Meeting (2) oAverage emittance of all bunches for log book oEmittance and integral of absolute of residuals per bunch as bar graph oAutomatic logging of emittance results after each scan − Also logging optics ID oCan retrieve profiles from logging and refit …fitting is not included yet Working on data sources …fitting is not included yet Working on data sources 11/12/2013 5

6. LHC Requirements from Last Meeting (3) oLaunch Multiple Scans − Display emittance/beam sigma versus time (also subscribe to energy and  *, optics ID) − Display mean versus time − Or…average over multiple scans …framework foresees this already …framework foresees this already 11/12/2013 6

7. LHC GUI – Mockup…..from Last Meeting 11/12/2013 7

8. LHC First Version of the New GUI Choose your acquisition mode: logging/hardware; single/multi Result for one or more scanners …scroll pane Result for one or more scanners …scroll pane Bunch-bunch result Profile for one bunch Configure scanners Configure multi acquisition (# scans per time unit) Configure logging access Default values for everything Configure scanners Configure multi acquisition (# scans per time unit) Configure logging access Default values for everything in/out 11/12/2013 8

9. LHC The New Philosophy oApplication works with objects WireScanner − Status − Beam − Plane − … − Scans oObject Scan − Timestamp − Bunch-by-bunch Profile data in/out, position − Optics ID − Energy  Optics and energy not on application level defined − Increased flexibility for online analysis of several scans e.g. through the ramp or through the squeeze 11/12/2013 9

10. LHC PART 2: Transverse Emittance Blow-up during the LHC Ramp 10 11/12/2013 oTransverse emittance measurements in 2012 oPossible sources of emittance blow-up during the LHC ramp

11. LHC Emittance Growth during the LHC Cycle oTotal average emittance blow-up during the cycle for 50 ns physics beams in 2012 ~ 0.7 – 1  m − Calculated from wire scans at injection and peak luminosity oTransverse emittances are mainly growing during the injection plateau and the ramp − Contribution of the ramp: ~ 20 % blow-up depending on the beam and the plane 11 11/12/2013 Sources of emittance growth during injection are intra beam scattering (IBS) and noise

12. LHC 11/12/2013 The LHC Ramp – A Closer Look oEnergy ramp from 450 GeV to 4 TeV in 2012 (13 min) oCAVEAT: Measurements during the ramp only possible with wire scanners only low intensity fills! measurement precision not verified (see later) oCloser look at beam 2 horizontal (Fill 3217) −  functions from k-modulation (linear interpolation between injection and flattop values) 12 Blow-up ~ 20 % (0.3  m) Similar for other MD fills Absolute blow-up is independent of initial emittance!

13. LHC Puzzling Results oIt seems the emittance evolution during the ramp is different for all planes. Why do we sometimes see decreasing emittances? 13 11/12/2013 Emittance blow-up during the ramp: Larger in the horizontal plane (15 – 30 %) than in the vertical plane (~ 5 %).

14. LHC Wire Scanners during the Ramp oHave to change voltage and filter settings of wire scanners during the ramp − This influences the measured beam sizes possibly due to photomultiplier saturation [1] − Resulting in large uncertainties up to ~ 0.5  m at injection and ~ 0.8  m at 4 TeV 14 11/12/2013 Measurement at 450 GeV But still cannot explain different emittance evolution for different planes because all wire scanners settings are changed similarly Leads to additional error on beam size!

15. LHC 2012 Test Cycles – Beam 1 Horizontal 15 11/12/2013 Emittance growth stops at around 2.5 TeV – shrinking emittances are puzzling 12 bunches/batch 6 bunches/batch

16. LHC 2012 Test Cycles – Beam 2 Horizontal 16 11/12/2013 Steeper slope of emittance growth during ramp starts only at around 1 TeV – before about the same growth as during injection plateau (IBS).

17. LHC Beam and Machine Parameters to Investigate oBeam profiles: should be Gaussian oBeam intensity oBunch length and longitudinal emittances oTune and beam lifetime oBBQ amplitudes oTransverse damper gain oDispersion oSnapback oCoupling oIBS oNoise oOptics oChromaticity o… 17 11/12/2013

18. LHC Beam and Machine Parameters to Investigate oBeam profiles: should be Gaussian oBeam intensity oBunch length and longitudinal emittances oTune and beam lifetime oBBQ amplitudes oTransverse damper gain oDispersion oSnapback oCoupling – could cause emittance growth in the vertical planes oIBS oNoise oOptics oChromaticity o… 18 11/12/2013 50 Hz noise and IBS cause emittance growth at the injection plateau

19. LHC The To Do List oFull IBS simulation through the ramp with MADX and CTE − To be compared to measurements oChromaticity measurements in 2012 oRe-analysis of 2012 beta functions measurements during the ramp oInfluence of optics correction functions through the ramp oEffect of transverse damping time − Pilot beam measurements? oEstimates of 50 Hz noise on emittance growth during the ramp − Use AC dipole model oTune spectra during the ramp oLongitudinal blow-up o(Vacuum) o… 19 11/12/2013

20. LHC Preliminary IBS Simulation Results oSimulations through the ramp are performed with MADX oIBS in the horizontal plane not negligible during the ramp 20 11/12/2013 For B2H and sometimes B1H the emittance growth at the start of the ramp is essentially IBS.

21. LHC Post LS1 Goals oWire scanner calibration − Including photomultiplier saturation curves oPilot beam measurements − To evaluate emittance growth in absence of transverse damper oAlternative transverse beam size measurement methods − Possibly Beam Gas Vertex detector (BGV) 21 11/12/2013 Thank you for your attention!

22. LHC Literature [1] M. Kuhn, " Emittance Preservation at the LHC, " Master Thesis, University of Hamburg/CERN, Geneva, Switzerland 2013. [2]O. S. Bruening, P. Collier, P. Lebrun, et al., " LHC Design Report - The LHC Main Ring, vol. 1., " CERN, 2004. [3]R. Steinhagen, "Real-Time Beam Control at the LHC," in Proceedings of 2011 Particle Accelerator Conferences, (New York, New York, USA), pp. 1399-1403, March 2011. [4]A. Langner, R. Calaga, R. Miyamoto, et al., "Optics Measurement in the LHC Close to the Half Integer Tune Resonance," CERN-ATS-Note-2011- 095 TECH, December 2011. 22 11/12/2013

23. LHC Back-up 23 11/12/2013

24. LHC Transverse Beam Profiles oTransverse profiles through the LHC cycle − Measured with wire scanners − Fitted the core of the profiles at 80 % intensity cut 24 11/12/2013 Transverse profiles through the entire LHC cycle are Gaussian! Very small error on the beam size from the Gauss fit

25. LHC Transverse Beam Profiles oTransverse profiles through the LHC cycle − Measured with wire scanners − Fitted the core of the profiles at 80 % intensity cut 25 11/12/2013

26. LHC Beam Intensity oBunch intensity stays almost constant during ramp − Has no influence on emittance evolution during the ramp 26 11/12/2013 Beam intensity measured with Fast Beam Current Transformer (FBCT) [2]

27. LHC 11/12/2013 Longitudinal Emittance during Ramp oBunch lengths are kept constant during the LHC ramp with targeted longitudinal blow-up − The blow-up is on during the entire ramp − The longitudinal RF blow-up during the LHC ramp is the same for both beams Except for the frequency: slightly higher for beam 2 than for beam 1 oLongitudinal emittance evolution cannot explain blow-up (decrease) in the transverse planes during the ramp 27

28. LHC Tune and Beam Lifetime for Fill 3217 28 11/12/2013 No visible peaks in tune signal Lifetimes: no indication for instabilities Beam 1 Beam 2 Energy Beam 1H Beam 1V Beam 2H Beam 2V Energy No hint from tune signal or beam lifetime for emittance growth during the ramp

29. LHC BBQ Amplitudes for Fill 3217 oBeam oscillation amplitudes increase after reducing the transverse damper gain at the start of the ramp − Measured with the LHC Base Band Tune (BBQ) monitors [3] − Reduction of transverse damper gain for sufficient tune signal during the ramp 29 11/12/2013 Large amplitudes at the of ramp for B2H – explanation for continuing blow-up at 4 TeV? Reduction of transverse damper gain No large beam oscillation amplitudes during the ramp – cannot explain emittance growth! Beam 1(H) Beam 1(V) Beam 2(H) Beam 2(V) Energy

30. LHC Dispersion oDispersion at the wire scanners is in the order of a few  m − Negligible compared to measured beam size − Not the reason for emittance blow-up during the ramp 30 11/12/2013  D 450 GeV 600 – 1000  m 0.1 m3.0 x 10 -4 4 TeV 200 – 400  m 0.2 – 0.3 m at 7 TeV1.3 x 10 -4 measured with wire scanners in 2012 for nominal LHC optics at location of wire scanners for 2012 LHC parameters

31. LHC Snapback oExample: Fill 2722 oTune trims during the ramp: oSnapback cannot explain continuous emittance growth during the ramp 31 11/12/2013 Beam 1H Beam 1V Beam 2H Beam 2V Energy Snapback is over at the very beginning of the ramp (~ 500 GeV)

32. LHC oEmittance growth in the vertical plane always smaller than in the horizontal plane oAcceptable coupling for normal LHC operation ~ 0.002 − For this fill beam 1 shows large coupling during the entire ramp − Beam 2 has strongly coupled planes at injection oCoupling could be an explanation for emittance growth in the vertical planes Coupling for Fill 3217 32 11/12/2013 threshold

33. LHC Optics Measurements oThe beta functions were measured through the ramp in 2012 − With turn-by-turn phase advance method at discrete energies at 1.3, 2.3, 3.0 TeV for beam 1 and at 1.3, 2.0, 2.6, 3.6 TeV for beam 2 − Large uncertainties because of not optimal phase advance between the BPMs and problems with the algorithm oMeasured beta functions through the ramp could therefore not be used for emittance determination − Used linear interpolation between injection and flattop values oDuring LS1: improvements of the algorithm − Expect re-calculated beta values through the ramp in December 33 11/12/2013

34. LHC Optics Corrections during Ramp oGlobal and local beta beat correction for both beams during the ramp: oIs there a visible effect on emittance growth during the ramp? − Caveat: global correction started in 2012 but there is also measurable emittance growth in 2011 34 11/12/2013 At 250 s = 1065 GeV during the LHC ramp the global beta beat for both beams is switched off.

35. LHC Optics Corrections during Ramp – B1 oIn general, emittance growth during the ramp in the horizontal plane stops ~ 2.5 TeV − emittances in the vertical are starting to shrink ~ 1.5 TeV 35 11/12/2013 Fill 2722: 2 x 12 nominal 50 ns bunches For some fills emittance growth in both planes of beam 1 is changing at ~ 1 TeV! But it is not clear, whether this evolution is correlated to optics corrections.

36. LHC Optics Corrections during Ramp – B2 oIn general, the slope of emittance growth of beam 2 horizontal becomes steeper at around 1 TeV during the LHC ramp − Is there a correlation to beta beat? 36 11/12/2013 Fill 3014: 2 x 6 nominal 50 ns bunches Emittances in the horizontal plane are growing more and in the vertical plane are shrinking at ~ 1 TeV!

37. LHC Summary Part 2 oMain unresolved emittance growth issue during the LHC cycle: source of blow-up during the ramp oEmittance growth during the ramp − Larger in the horizontal plane (15 – 30 %) than in the vertical plane (~ 5 %) − Causes are unclear oPuzzling results: − Beam 1 horizontal: growth stops at ~ 2.5 TeV − Beam 2 horizontal: continuously grows through ramp, sometimes even still on flattop growth steeper slope after > 1 TeV, before probably essentially IBS − No common pattern of emittance blow-up during the ramp in the different planes Sometimes even decreasing emittances (especially in B1H, B1V and B2V) 37 11/12/2013

38. LHC Conclusion Part 2 (1) oPossible sources that can be excluded − Non Gaussian profiles, intensity losses, longitudinal emittance evolution, tune, beam lifetime, reduced transverse damper gain, dispersion oPuzzling results: − Independent of initial emittance same absolute emittance growth Indication of problem’s origin - noise? But higher transverse damper gain does not help And no clear indication from beam oscillation amplitudes oHow trustable are transverse profile monitors (wire scanners)? − Wire scanner photomultiplier saturation during the ramp − But asymmetry cannot be explained by changing wire scanner settings − Measurements in ATLAS, CMS and LHCb suggest even more emittance blow-up during the LHC cycle 38 11/12/2013

39. LHC Conclusion Part 2 (2) oSpeculating growth in vertical plane comes from coupling oIBS contributes to growth during ramp in the horizontal plane − IBS growth rate decreases only very slowly with energy, negligible only from ~ 2 - 3 TeV (depending on initial emittance) − BUT: IBS cannot explain growth during ramp - growth rate is larger during ramp than at injection oMeasurement of beta functions through the ramp could help to understand the problems oOptics corrections through the ramp influence emittance evolution during the ramp: beta beat is switched off at 1065 GeV in the ramp − For beam 2 horizontal that could explain the steeper emittance growth starting at the same time − All other planes indicate no correlation to beta beat or show shrinking emittances at that time 39 11/12/2013