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Updates on the LHC Wire Scanner Application --- Transverse Emittance Blow-up during the LHC Ramp

Updates on the LHC Wire Scanner Application --- Transverse Emittance Blow-up during the LHC Ramp. Verena Kain, Maria Kuhn. Outline. PART 1 Updates on the LHC wire scanner application Requirements from last meeting First version of the new GUI The new philosophy PART 2

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Updates on the LHC Wire Scanner Application --- Transverse Emittance Blow-up during the LHC Ramp

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

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

  3. PART 1:Updates on the LHC Wire Scanner Application 11/12/2013 • Requirements from last meeting • First version of the new GUI • The new philosophy

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

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

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

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

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

  9. The New Philosophy 11/12/2013 • Application works with objects WireScanner • Status • Beam • Plane • … • Scans • Object 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

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

  11. Emittance Growth during the LHC Cycle • Sources of emittance growth during injection are intra beam scattering (IBS) and noise 11/12/2013 • Total average emittance blow-up during the cycle for 50 ns physics beams in 2012 ~ 0.7 – 1 mm • Calculated from wire scans at injection and peak luminosity • Transverse 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

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

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

  14. Wire Scanners during the Ramp Measurement at 450 GeV Leads to additional error on beam size! • But still cannot explain different emittance evolution for different planes because all wire scanners settings are changed similarly 11/12/2013 • Have 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 mm at injection and ~ 0.8 mm at 4 TeV

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

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

  17. Beam and Machine Parameters to Investigate 11/12/2013 Beam profiles: should be Gaussian Beam intensity Bunch length and longitudinal emittances Tune and beam lifetime BBQ amplitudes Transverse damper gain Dispersion Snapback Coupling IBS Noise Optics Chromaticity …

  18. Beam and Machine Parameters to Investigate 50 Hz noise and IBS cause emittance growth at the injection plateau 11/12/2013 Beam profiles: should be Gaussian Beam intensity Bunch length and longitudinal emittances Tune and beam lifetime BBQ amplitudes Transverse damper gain Dispersion Snapback Coupling – could cause emittance growth in the vertical planes IBS Noise Optics Chromaticity …

  19. The To Do List 11/12/2013 • Full IBS simulation through the ramp with MADX and CTE • To be compared to measurements • Chromaticity measurements in 2012 • Re-analysis of 2012 beta functions measurements during the ramp • Influence of optics correction functions through the ramp • Effect of transverse damping time • Pilot beam measurements? • Estimates of 50 Hz noise on emittance growth during the ramp • Use AC dipole model • Tune spectra during the ramp • Longitudinal blow-up • (Vacuum) • …

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

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

  22. Literature 11/12/2013 [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.

  23. Back-up 11/12/2013

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

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

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

  27. Longitudinal Emittance during Ramp 11/12/2013 • Bunch 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 • Longitudinal emittance evolution cannot explain blow-up (decrease) in the transverse planes during the ramp

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

  29. BBQ Amplitudes for Fill 3217 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 Reduction of transverse damper gain Large amplitudes at the of ramp for B2H – explanation for continuing blow-up at 4 TeV? 11/12/2013 • Beam 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

  30. Dispersion Beam size from dispersion:30 mm 11/12/2013 • Dispersion at the wire scanners is in the order of a few mm • Negligible compared to measured beam size • Not the reason for emittance blow-up during the ramp

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

  32. Coupling for Fill 3217 threshold 11/12/2013 • Emittance growth in the vertical plane always smaller than in the horizontal plane • Acceptable 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 • Coupling could be an explanation for emittance growth in the vertical planes

  33. Optics Measurements 11/12/2013 • The 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 • Measured beta functions through the ramp could therefore not be used for emittance determination • Used linear interpolation between injection and flattop values • During LS1: improvements of the algorithm • Expect re-calculated beta values through the ramp in December

  34. Optics Corrections during Ramp At 250 s = 1065 GeV during the LHC ramp the global beta beat for both beams is switched off. 11/12/2013 • Global and local beta beat correction for both beams during the ramp: • Is 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

  35. Optics Corrections during Ramp – B1 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. Fill 2722: 2 x 12 nominal 50 ns bunches 11/12/2013 • In 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

  36. Optics Corrections during Ramp – B2 Emittances in the horizontal plane are growing more and in the vertical plane are shrinking at ~ 1 TeV! Fill 3014: 2 x 6 nominal 50 ns bunches 11/12/2013 • In 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?

  37. Summary Part 2 11/12/2013 • Main unresolved emittance growth issue during the LHC cycle: source of blow-up during the ramp • Emittance growth during the ramp • Larger in the horizontal plane (15 – 30 %) than in the vertical plane (~ 5 %) • Causes are unclear • Puzzling 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)

  38. Conclusion Part 2 (1) 11/12/2013 • Possible sources that can be excluded • Non Gaussian profiles, intensity losses, longitudinal emittance evolution, tune, beam lifetime, reduced transverse damper gain, dispersion • Puzzling 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 • How 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

  39. Conclusion Part 2 (2) 11/12/2013 • Speculating growth in vertical plane comes from coupling • IBS 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 • Measurement of beta functions through the ramp could help to understand the problems • Optics 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

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