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

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

LHC Wire Scanner Calibration M. Kuhn - 28/07/2015

Orbit Bump Calibration (1) 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 % B2V1 ~ slope difference + 3 % M. Kuhn - 28/07/2015

Orbit Bump Calibration (2) Summary of results: Mostly emittances are overestimated by LHC wire scanners Exception: B1V2 Best would be to correct the calibration factor on the front-end Would need another measurement to check reproducibility of results 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 % M. Kuhn - 28/07/2015

Photomultiplier Saturation Studies Run 1 Photomultiplier (PM) gain and filter can have a strong influence on measured beam size See measurements of 2012 Observed strong gain dependence at 450 GeV and 4 TeV during Run 1! PM saturation studies at 450 GeV in 2012. PM saturation studies at 4 TeV in 2012. M. Kuhn - 28/07/2015

Photomultiplier Saturation Studies Run 2 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 Studies at 6.5 TeV more difficult – very small range of settings Nominal betas used 6.5 TeV 450 GeV M. Kuhn - 28/07/2015

PM Saturation Studies @ 450 GeV 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 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. M. Kuhn - 28/07/2015

Resumé Wire Scanner Accuracy 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 No PM saturation effects with single bunches PM saturation might have to be revised for trains NEWS: Emiliano et al will further investigate optimum working point in the lab 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 3 wire scans to get reliable measurement M. Kuhn - 28/07/2015

Optics measurements M. Kuhn - 28/07/2015

LHC Optics Measurements Can use results from optics measurements with the turn-by-turn phase advance method and k-modulation for: 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! Now using measured beta functions where possible! Measurement error < 3 % Maximum measured beta beat is 5 % at the wire scanners IR4 IP1/2/5/8 Injection Ramp Flattop After Squeeze b* K-modulation x Turn-by-turn M. Kuhn - 28/07/2015

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

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

Wire scanner Intensity limits M. Kuhn - 28/07/2015

Wire Scanner Intensity Limits Limits so far: Maximum 2.7 x 1013 protons per beam at 450 GeV Corresponds to ~ 240 nominal bunches Maximum 2.3 x 1011 protons per beam at 6.5 TeV Corresponds to ~ 2 nominal bunches New Limit: maximum 1.6 x 1012 protons per beam at 6.5 TeV Corresponds to ~ 10 - 14 nominal bunches To be implemented soon Run 2: rely even more on an operational BSRT M. Kuhn - 28/07/2015

Emittance growth during the cycle M. Kuhn - 28/07/2015

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

Emittance Growth in Numbers: Fill 3954 Average emittance of 4 scans SPS emittance at extraction: H = 2.16 mm, V = 2.0 mm Adding additional 10 % uncertainty on wire scanner position measurement Fill 3954, Bunch 1 Injection Collision De [mm] De/e [%] B1H e [mm] 2.66 ± 0.14 2.95 ± 0.16 0.29 ± 0.21 11 ± 18 B1V 2.40 ± 0.11 2.80 ± 0.13 0.40 ± 0.17 17 ± 17 B2H 2.12 ± 0.08 2.14 ± 0.18 0.02 ± 0.20 1 ± 19 B2V 2.85 ± 0.07 3.14 ± 0.32 0.29 ± 0.32 10 ± 21 M. Kuhn - 28/07/2015

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

Emittance Growth vs. IBS – Beam 1 Beam 1 horizontal grows more strongly than IBS suggests Origin of growth in the vertical plane? Nominal betas used Bunch 1 Bunch 2 M. Kuhn - 28/07/2015

Beam Parameters Fill 3954 M. Kuhn - 28/07/2015

Measurements Reproducible? (1) Fill 3809 (June 1, 2015): With measured beta M. Kuhn - 28/07/2015

Beam Parameters Fill 3809 M. Kuhn - 28/07/2015

Measurements Reproducible? (2) Fill 3939 (June 30, 2015): With measured beta M. Kuhn - 28/07/2015

Bunch length reduction could explain emittance evolution Beam Parameters Fill 3939 Bunch length reduction could explain emittance evolution M. Kuhn - 28/07/2015

Measurements Reproducible? (3) A more recent Fill 4039 (July 24, 2015): With measured beta M. Kuhn - 28/07/2015

Beam Parameters Fill 4039 M. Kuhn - 28/07/2015

Measurements Reproducible? (4) A more recent Fill 4040 (July 24, 2015): With measured beta M. Kuhn - 28/07/2015

Beam Parameters Fill 4040 M. Kuhn - 28/07/2015

Average Absolute Emittance Growth To better visualize the average growth overlaying all ramps B1H: ~ 0.2 mm blow-up, reproducible fluctuation during the ramp. B1V and B2H no blow-up. B2V: ~ 0.2 mm blow-up, large error bars from in-out-scan deviations. M. Kuhn - 28/07/2015

Average Relative Emittance Growth B1H: ~ 10 % blow-up, reproducible fluctuation during the ramp. B1V and B2H no blow-up. B2V: ~ 10 % blow-up, large error bars from in-out-scan deviations. M. Kuhn - 28/07/2015

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

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

BSRT Measurements at 6.5 TeV Stable beams Fill 3996 July 14, 2015 476 bunches ~ 3.5 hours in collision Average emittance growth from BSRT and ATLAS/CMS luminosity ATLAS Measured betas used (tbt) CMS M. Kuhn - 28/07/2015

Emittance from Luminosity 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 % 5 % error on crossing angle and 10 % error on b* should be added Preliminary: ATLAS and wire scanner results agree within errors! Better than during Run 1 Need measured optics for final comparison Fill 3954, Bunch 1 Injection Collision Growth WS e [mm] 2.51 ± 0.10 2.75 ± 0.20 0.24 10 % ATLAS e [mm] 2.97 ± 0.36 0.46 19 % CMS e [mm] 4.01 ± 0.47 1.5 64 % M. Kuhn - 28/07/2015

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

Reminder: 2012 Emittance Blow-up 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 M. Kuhn - 28/07/2015

Summary 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 For some fills the emittances seem to be growing in all planes through the cycle and mainly during injection plateau and ramp Origins: IBS ? With the still not fully calibrated luminosity data: better agreement between wire scans and emittance from luminosity Luminosity measurements (ATLAS) over the last weeks indicate small growth through the cycle M. Kuhn - 28/07/2015

To Do Optics measurements in point 4 b* measurements 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 b* measurements Repeat orbit bump scans – to check reproducibility Understand additional sources of growth! LHC OP please don’t forget to do wire scans at injection in all planes. Thank you! M. Kuhn - 28/07/2015