lhc lhc emittance measurements and preservation lboc meeting july 28, 2015 maria kuhn – july 28,...
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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.
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Outlineo Accuracy of LHC emittance measurements with wire scanners
− Wire scanner calibration
• Orbit bumps
• Photomultiplier saturation studies
− LHC optics measurements
o Wire scanner intensity thresholds
o Emittance growth during the LHC cycle
− Injection plateau and IBS
− BSRT measurements
− Comparison with emittance from luminosity
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LHC WIRE SCANNER CALIBRATION
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Orbit Bump Calibration (1)o Using 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 %
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B2V1 ~ slope difference + 3 %
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Orbit Bump Calibration (2)o Summary of results:
o Mostly emittances are overestimated by LHC wire scanners
− Exception: B1V2
o Best would be to correct the calibration factor on the front-end
− Would need another measurement to check reproducibility of results
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Wire Scanner Error on position Error on emittance
B1H2 + 3.6 % + 7.2 %B1V2 - 2.6 % - 5.2 %B2H1 + 4.5 % + 9 %B2V1 + 3.3 % + 6.6 %
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Photomultiplier Saturation Studies Run 1
o Photomultiplier (PM) gain and filter can have a strong influence on measured beam size
− See measurements of 2012
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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!
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Photomultiplier Saturation Studies Run 2
o Studies 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
o Studies at 6.5 TeV more difficult – very small range of settings
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6.5 TeV
450 GeV
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PM Saturation Studies @ 450 GeV
o Beam 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
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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.
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Resumé Wire Scanner Accuracyo Possibly “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
o No PM saturation effects with single bunches
− PM saturation might have to be revised for trains
o Fairly 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
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OPTICS MEASUREMENTS
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LHC Optics Measurementso Can use results from optics measurements with the turn-by-turn
phase advance method and k-modulation for:
o Outstanding 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!
o Current maximum beta beat is 10 % at the wire scanners
− Adds another maximum uncertainty on emittance of 10 %
o Currently still using nominal beta functions in the plots
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IR4 IP1/2/5/8
Injection Ramp Flattop After Squeeze b*
K-modulation xTurn-by-turn x x
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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
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Want precision emittance measurements;Need most accurate optics measurements.
A. Langner
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Motivation: More K-Modulation Measurements
o Recent k-modulation measurement in the LHC (23. July)
− IP1 at 3 m b*
− Pilot bunch without tune chirp
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Very promising results, measurement error on tune oscillation in sub-percent level!
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WIRE SCANNER INTENSITY LIMITS
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Wire Scanner Intensity LimitsLimits so far:
o Maximum 2.7 x 1013 protons per beam at 450 GeV
− Corresponds to ~ 240 nominal bunches
o Maximum 2.3 x 1011 protons per beam at 6.5 TeV
− Corresponds to ~ 2 nominal bunches
o New Limit: maximum 1.6 x 1012 protons per beam at 6.5 TeV
− Corresponds to ~ 10 - 14 nominal bunches
− To be implemented soon
o Run 2: rely even more on an operational BSRT
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EMITTANCE GROWTH DURING THE CYCLE
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squeeze
Emittance Evolution during the Cycle
o Require: measured beta function through the entire cycle
o Fill 3954 (July 4, 2015)
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Partly unphysical emittance evolution!
From Run 1 experience:optics
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Emittance Growth in Numbers: Fill 3954
o Average emittance of 4 scans
o SPS emittance at extraction: H = 2.16 mm, V = 2.0 mm
o Caveat: nominal beta functions!
− Adding 10 % uncertainty on b and 10 % uncertainty on wire scanner position measurement
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Fill 3954, Bunch 1 Injection Collision De [mm] /De e [%]
B1H e [mm] 2.66 3.18 0.09 20 ± 20B1V e [mm] 2.37 2.79 0.14 16 ± 20B2H e [mm] 2.16 2.23 0.04 6 ± 20B2V e [mm] 2.84 3.08 -0.06 -7 ± 20
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Emittance Growth vs. IBS – Beam 2
o IBS simulations with MADX IBS module
− Including: dispersion, radiation effects, measured bunch length through cycle, measured initial intensity and emittance
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Bunch 2
Bunch 1
IBS could fit evolution in horizontal plane.
Need optics through the ramp for vertical plane.
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Emittance Growth vs. IBS – Beam 1
o Beam 1 horizontal grows more strongly than IBS suggests
o Origin of growth in the vertical plane?
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Bunch 1
Bunch 2
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Measurements Reproducible? (1)
o Fill 3809 (June 1, 2015):
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Measurements Reproducible? (2)
o Fill 3939 (June 30, 2015):
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Measurements Reproducible? (3)
o A more recent Fill 4039 (July 24, 2015):
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Measurements Reproducible? (4)
o A more recent Fill 4040 (July 24, 2015):
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BSRT Measurements at 450 GeVo Example Fill 3808, June 1, 2015
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BSRT measurement
Wire scanner measurement
6 nominal bunches with different beam sizes.
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BSRT Measurements at 450 GeVo A more recent Fill 4034 (July 22, 2015):
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BSRT and wire scanner measure large growth in the vertical planes.
BSRT smaller scatter than wire scanner.
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BSRT Measurements at 6.5 TeVo Stable beams Fill 3996
− July 14, 2015
− 476 bunches
− ~ 3.5 hours in collision
− Average emittance growth from BSRT and ATLAS/CMS luminosity
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ATLAS
CMS
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Emittance from Luminosityo Comparison 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 %
o Preliminary: ATLAS and wire scanner results agree within errors!
− Better than during Run 1
− Need measured optics for final comparison
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Fill 3954, Bunch 1 Injection Collision GrowthWire Scanner e [mm] 2.51 ± 0.09 2.82 ± 0.18 0.31 12 %WS with meas. b e [mm] 2.75 ± 0.20 0.24 10 %ATLAS e [mm] 2.97 ± 0.36 0.46 19 %ATLAS corrected 2.65 ± 0.32 0.14 6 %CMS e [mm] 4.01 ± 0.47 1.5 64 %CMS corrected 3.67 ± 0.43 1.16 46 %
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Comparison SPS – LHC - Luminosity
o Convoluted emittance (H + V) of SPS wire scans at 450 GeV
o Emittance per plane of LHC wire scans at 450 GeV
− Lacking scans in the LHC!
o Convoluted emittance from ATLAS and CMS luminosity
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Results seem to indicate less growth through the cycle than in 2012.
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o Overall average transverse normalized emittance blow-up through the LHC cycle:
− ~ 0.4 – 0.9 mm from injection into the LHC to start of collision (convoluted e) for the first injected batch of 144 bunches per beam
Reminder: 2012 Emittance Blow-up
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A Propos Tails (1)o Beam profile measured with wire scanner at injection
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A Propos Tails (2)o Beam profile measured with wire scanner at injection
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Not possible at 6.5 TeV due to less points
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Summaryo Good 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
o For some fills the emittances seem to be growing in all planes through the cycle and mainly during injection plateau and ramp
o Origins:
− IBS
− ?
o With the still not fully calibrated luminosity data: better agreement between wire scans and emittance from luminosity
o Luminosity measurements (ATLAS) over the last weeks indicate small growth through the cycle
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To Doo Optics 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
o b* measurements
o Repeat orbit bump scans – to check reproducibility
o Understand additional sources of growth!
o LHC OP please don’t forget to do wire scans at injection in all planes.
Thank you!
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APPENDIX
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Emittance Growth in Numberso Average emittance of 4 scans
o SPS emittance at extraction: H = 2.16 mm, V = 2.0 mm
o Caveat: nominal beta functions!
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Fill 3954, Bunch 1
Injec-tion Ramp Squeeze
Colli-sions Total
B1H e [mm] 2.66 2.75 3.33 3.47 3.18 3.18
De [mm] 0.09 (3 %)
0.58 (21 %) -0.29 (- 8 %)
0.52 (20 %)
B1V e [mm] 2.37 2.51 2.65 2.73 2.76 2.79
De [mm] 0.14 (6 %) 0.14 (6 %) 0.03 (1 %)
0.39 (16 %)
B2H e [mm] 2.16 2.20 2.23 2.24 2.29 2.23
De [mm] 0.04 (2 %) 0.03 (1 %) 0.06 (3 %) 0.14 (6 %)
B2V e [mm] 2.84 2.78 3.27 3.26 2.64 3.08
De [mm]
-0.06 (-2 %)
0.49 (18 %) -0.61 (-19 %)
-0.20 (-7 %)
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Emittance Growth vs. IBS – Beam 1
o IBS Simulations Fill 3954 beam 1 with larger initial emittances
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Bunch 2
Bunch 1
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Emittance Blow-up during the Ramp
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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 e [mm] 2.75 3.33De [mm] 0.58 (21 %)
B1V e [mm] 2.51 2.65De [mm] 0.14 (6 %)
B2H e [mm]2.20 2.23
De [mm] 0.03 (1 %)
B2V e [mm]2.78 3.27
De [mm] 0.49 (18 %)
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Emittances during the Squeeze
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Average Emittance during the Squeeze
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Fill 3954, Bunch 1 Squeeze
B1H e [mm] 3.47 3.18De [mm] -0.29 (- 8 %)
B1V e [mm] 2.73 2.76De [mm] 0.03 (1 %)
B2H e [mm] 2.24 2.29De [mm] 0.06 (3 %)
B2V e [mm] 3.26 2.64De [mm]
-0.61 (-19 %)
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Comparison SPS – LHC - Luminosity
o Convoluted emittance (H + V) of SPS wire scans at 450 GeV
o Emittance per plane of LHC wire scans at 450 GeV
− Lacking scans in the LHC!
o Convoluted emittance from ATLAS and CMS luminosity
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With corrected luminosity – indicates very little growth. Preliminary, to be followed up after luminosity calibration.
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Emittance from LuminosityATLAS (Witold):
o Currently logged luminosity uses a very rough calibration based on a quick scan performed on 28 May 2015.
o The 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%.
o In other words, for the data up to the MD of 20 July, the L scale is off by (-10 +- 10) %. 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 )
o We 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
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