LHC LHC Emittance Measurements and Preservation LBOC Meeting July 28, 2015 Maria Kuhn – July 28, 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.

LHC Outline oAccuracy of LHC emittance measurements with wire scanners − Wire scanner calibration Orbit bumps Photomultiplier saturation studies − LHC optics measurements oWire scanner intensity thresholds oEmittance growth during the LHC cycle − Injection plateau and IBS − BSRT measurements − Comparison with emittance from luminosity 2 M. Kuhn - 28/07/2015

LHC LHC WIRE SCANNER CALIBRATION 3 M. Kuhn - 28/07/2015

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 - 28/07/2015 B2V1 ~ slope difference + 3 %

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 - 28/07/2015 Wire ScannerError on positionError on emittance B1H %+ 7.2 % B1V %- 5.2 % B2H %+ 9 % B2V %+ 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 M. Kuhn - 28/07/2015 PM saturation studies at 4 TeV in 2012.PM saturation studies at 450 GeV in Observed strong gain dependence at 450 GeV and 4 TeV during Run 1!

LHC Photomultiplier Saturation Studies Run 2 oStudies at 450 GeV with 6 bunches of different emittances: − Systematically changing gain and filter of PMs 2500 < profile amplitudes < 7500 (no ADC saturation) − Example scanner B2H1, other planes look similar oStudies at 6.5 TeV more difficult – very small range of settings 7 M. Kuhn - 28/07/ TeV 450 GeV

LHC PM Saturation 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 8 M. Kuhn - 28/07/2015 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.

LHC Resumé 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 % emittance measurement error oNo PM saturation effects with single bunches − PM saturation might have to be revised for trains 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 4 wire scans to get reliable measurement 9 M. Kuhn - 28/07/2015

LHC OPTICS MEASUREMENTS 10 M. Kuhn - 28/07/2015

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! oCurrent maximum beta beat is 10 % at the wire scanners − Adds another maximum uncertainty on emittance of 10 % oCurrently still using nominal beta functions in the plots 11 M. Kuhn - 28/07/2015 IR4IP1/2/5/8 InjectionRampFlattopAfter Squeeze ** K-modulation x Turn-by-turn xx

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 12 M. Kuhn - 28/07/2015 Want precision emittance measurements; Need most accurate optics measurements. A. Langner

LHC Motivation: More K-Modulation Measurements oRecent k-modulation measurement in the LHC (23. July) − IP1 at 3 m  * − Pilot bunch without tune chirp 13 M. Kuhn - 28/07/2015 Very promising results, measurement error on tune oscillation in sub- percent level!

LHC WIRE SCANNER INTENSITY LIMITS 14 M. Kuhn - 28/07/2015

LHC Wire Scanner Intensity Limits Limits so far: oMaximum 2.7 x protons per beam at 450 GeV − Corresponds to ~ 240 nominal bunches oMaximum 2.3 x protons per beam at 6.5 TeV − Corresponds to ~ 2 nominal bunches oNew Limit: maximum 1.6 x protons per beam at 6.5 TeV − Corresponds to ~ nominal bunches − To be implemented soon oRun 2: rely even more on an operational BSRT 15 M. Kuhn - 28/07/2015

LHC EMITTANCE GROWTH DURING THE CYCLE 16 M. Kuhn - 28/07/2015

LHC squeeze Emittance Evolution during the Cycle oRequire: measured beta function through the entire cycle oFill 3954 (July 4, 2015) 17 M. Kuhn - 28/07/2015 Partly unphysical emittance evolution! From Run 1 experience: optics

LHC Emittance Growth in Numbers: Fill 3954 oAverage emittance of 4 scans oSPS emittance at extraction: H = 2.16  m, V = 2.0  m oCaveat: nominal beta functions! − Adding 10 % uncertainty on  and 10 % uncertainty on wire scanner position measurement 18 M. Kuhn - 28/07/2015 Fill 3954, Bunch 1InjectionCollision  [  m]  [  ] B1H  [  m] ± 20 B1V  [  m] ± 20 B2H  [  m] ± 20 B2V  [  m] ± 20

LHC Emittance Growth vs. IBS – Beam 2 oIBS simulations with MADX IBS module − Including: dispersion, radiation effects, measured bunch length through cycle, measured initial intensity and emittance 19 M. Kuhn - 28/07/2015 Bunch 2 Bunch 1 IBS could fit evolution in horizontal plane. Need optics through the ramp for vertical plane.

LHC Emittance Growth vs. IBS – Beam 1 oBeam 1 horizontal grows more strongly than IBS suggests oOrigin of growth in the vertical plane? 20 M. Kuhn - 28/07/2015 Bunch 1 Bunch 2

LHC Measurements Reproducible? (1) oFill 3809 (June 1, 2015): 21 M. Kuhn - 28/07/2015

LHC Measurements Reproducible? (2) oFill 3939 (June 30, 2015): 22 M. Kuhn - 28/07/2015

LHC Measurements Reproducible? (3) oA more recent Fill 4039 (July 24, 2015): 23 M. Kuhn - 28/07/2015

LHC Measurements Reproducible? (4) oA more recent Fill 4040 (July 24, 2015): 24 M. Kuhn - 28/07/2015

LHC BSRT Measurements at 450 GeV oExample Fill 3808, June 1, M. Kuhn - 28/07/2015 BSRT measurement Wire scanner measurement 6 nominal bunches with different beam sizes.

LHC BSRT Measurements at 450 GeV oA more recent Fill 4034 (July 22, 2015): 26 M. Kuhn - 28/07/2015 BSRT and wire scanner measure large growth in the vertical planes. BSRT smaller scatter than wire scanner.

LHC BSRT Measurements at 6.5 TeV oStable beams Fill 3996 − July 14, 2015 − 476 bunches − ~ 3.5 hours in collision − Average emittance growth from BSRT and ATLAS/CMS luminosity 27 M. Kuhn - 28/07/2015 ATLAS CMS

LHC 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 % oPreliminary: ATLAS and wire scanner results agree within errors! − Better than during Run 1 − Need measured optics for final comparison 28 M. Kuhn - 28/07/2015 Fill 3954, Bunch 1InjectionCollisionGrowth Wire Scanner  [  m] 2.51 ± ± % WS with meas.  [  m] 2.75 ± % ATLAS  [  m] 2.97 ± % ATLAS corrected 2.65 ± % CMS  [  m] 4.01 ± % CMS corrected 3.67 ± %

LHC Comparison SPS – LHC - Luminosity oConvoluted emittance (H + V) of SPS wire scans at 450 GeV oEmittance per plane of LHC wire scans at 450 GeV − Lacking scans in the LHC! oConvoluted emittance from ATLAS and CMS luminosity 29 M. Kuhn - 28/07/2015 Results seem to indicate less growth through the cycle than in 2012.

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 30 M. Kuhn - 28/07/2015

LHC A Propos Tails (1) oBeam profile measured with wire scanner at injection 31 M. Kuhn - 28/07/2015

LHC A Propos Tails (2) oBeam profile measured with wire scanner at injection 32 M. Kuhn - 28/07/2015 Not possible at 6.5 TeV due to less points

LHC Summary oGood progress with understanding the wire scanner emittance measurements − In general seem to be in a better shape than during Run 1 − More optics measurements are required And upload into DB oFor some fills the emittances seem to be growing in all planes through the cycle and mainly during injection plateau and ramp oOrigins: − IBS − ? oWith the still not fully calibrated luminosity data: better agreement between wire scans and emittance from luminosity oLuminosity measurements (ATLAS) over the last weeks indicate small growth through the cycle 33 M. Kuhn - 28/07/2015

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  * measurements oRepeat orbit bump scans – to check reproducibility oUnderstand additional sources of growth! oLHC OP please don’t forget to do wire scans at injection in all planes. Thank you! 34 M. Kuhn - 28/07/2015

LHC APPENDIX 35 M. Kuhn - 28/07/2015

LHC Emittance Growth in Numbers oAverage emittance of 4 scans oSPS emittance at extraction: H = 2.16  m, V = 2.0  m oCaveat: nominal beta functions! 36 M. Kuhn - 28/07/2015 Fill 3954, Bunch 1 Injec- tion RampSqueeze Colli- sions Total B1H  [  m]  [  m] 0.09 (3 %)0.58 (21 %)-0.29 (- 8 %)0.52 (20 %) B1V  [  m]  [  m] 0.14 (6 %) 0.03 (1 %)0.39 (16 %) B2H  [  m]  [  m] 0.04 (2 %)0.03 (1 %)0.06 (3 %)0.14 (6 %) B2V  [  m]  [  m] (-2 %)0.49 (18 %)-0.61 (-19 %)-0.20 (-7 %)

LHC Emittance Growth vs. IBS – Beam 1 oIBS Simulations Fill 3954 beam 1 with larger initial emittances 37 M. Kuhn - 28/07/2015 Bunch 2 Bunch 1

LHC Emittance Blow-up during the Ramp 38 M. Kuhn - 28/07/2015 Small emittance blow-up at the end of the ramp in B1H and B2V. Preliminary! Missing measured beta functions. Fill 3954, Bunch 1 Ramp B1H  [  m]  [  m] 0.58 (21 %) B1V  [  m]  [  m] 0.14 (6 %) B2H  [  m]  [  m] 0.03 (1 %) B2V  [  m]  [  m] 0.49 (18 %)

LHC Emittances during the Squeeze 39 M. Kuhn - 28/07/2015

LHC Average Emittance during the Squeeze 40 M. Kuhn - 28/07/2015 Fill 3954, Bunch 1 Squeeze B1H  [  m]  [  m] (- 8 %) B1V  [  m]  [  m] 0.03 (1 %) B2H  [  m]  [  m] 0.06 (3 %) B2V  [  m]  [  m] (-19 %)

LHC Comparison SPS – LHC - Luminosity oConvoluted emittance (H + V) of SPS wire scans at 450 GeV oEmittance per plane of LHC wire scans at 450 GeV − Lacking scans in the LHC! oConvoluted emittance from ATLAS and CMS luminosity 41 M. Kuhn - 28/07/2015 With corrected luminosity – indicates very little growth. Preliminary, to be followed up after luminosity calibration.

LHC Emittance from Luminosity ATLAS (Witold): oCurrently logged luminosity uses a very rough calibration based on a quick scan performed on 28 May oThe central value of the luminosity that we publish currently is now known to be low by 10%. Once we fix this (during the MD), using a better scan taken on June 10, the new L scale will have a systematic uncertainty of around +- 10%. oIn other words, for the data up to the MD of 20 July, the L scale is off by ( ) %. The data recorded after July 20 will have the best calibration we know (even if still pretty rough) and will have an associated uncertainty around +- 10%. CMS (David Stickland ) oWe are completing the analysis at this moment. We expect that our currently published Lumi and Lumi/bx is about 10% low and we would assign a 10% uncertainty on the luminosity after correction by the 10% shift 42 M. Kuhn - 28/07/2015