LHC Wire Scanner Calibration Emittance Meeting June 10, 2015 LHC Wire Scanner Calibration Maria Kuhn – June 10, 2015

Motivation Goal for LHC commissioning: operational emittance measurement tools at end of first two months with beam Measure optics Results will be presented in a later meeting For today‘s plots nominal beta functions are used! Obtain optimum wire scanner working point Orbit bump calibration and photomultiplier saturation studies Operational BSRT Cross-calibration with wire scanners Quantify emittance growth through the LHC cycle Puzzle: emittance from wire scans vs emittance from lumi not conclusive!! M. Kuhn - 10/06/2015

Reminder LHC Commissioning Plan We were able to profit from 2 months LHC commissioning  Almost completed commissioning of emittance measurement devices! LHC commissioning period is extended Van der Meer scans are postponed to after the scrubbing run! Beginning of July! Measurements during collisions and with LHCb SMOG are already in the planning June 10th M. Kuhn - 10/06/2015

Tasks during LHC Commissioning Task for Wire Scanner Commissioning Injection energy Flattop energy Confirm BLM thresholds:  find wire scan limits ~ 30 min Orbit bump calibration:  validate calibration of all eight wire scanners ~ 80 min Qualify photo-multiplier saturation:  find optimum wire scanner working points ~ 180 min Finished all of these tasks during LHC commissioning phase Only for the 4 operational wire scanners: B1H2, B1V2, B2H1, B2V1 We will keep using these scanners only (if possible) M. Kuhn - 10/06/2015

Wire Scanner Intensity Limits Confirmed thresholds: Maximum 144 bunches at 450 GeV Corresponds to the 1st 50 ns bunch batch in the LHC Maximum 2.3 x 1011 protons at 6.5 TeV Corresponds to ~ 2 nominal bunches During scans at 6.5 TeV with ~ 2.3 x 1011 protons per beam we saw more than 30 % losses  Rely even more on a working BSRT 100 times loss/threshold 30 % E. Piselli M. Kuhn - 10/06/2015

Orbit Bump Calibration Beam 1 Beam 1 orbit bumps on May 14, 2015 and June 1, 2015 Wire scanner (and BSRT in parallel) 450 GeV and 6.5 TeV Calibrated scanners: B1H2 and B1V2 Calibration for BSRT B1V not completed! Here we take average of in and out scan – is that feasable? Uncertainties on position measurement: B1H = 2 % B1V = 7 % preliminary preliminary M. Kuhn - 10/06/2015

Orbit Bump Calibration Beam 2 Beam 2 orbit bumps on April 24, 2015 Wire scanner and BSRT in parallel 450 GeV and 6.5 TeV Calibrated scanners: B2H1 and B2V1 Uncertainties on position measurement: B2H = 0 % B2V = 4 % Uncertainties in the vertical planes are larger To be verified...see later slides preliminary preliminary M. Kuhn - 10/06/2015

Photomultiplier Saturation at 450 GeV Scanned through all possible gain and filter combinations Always scanned with reference settings in between Goal: find optimum wire scanner working point Injected 6 bunches and blew up to different emittances Exponential fit of scans with reference settings to take out effect of growth at injection plateau: Max spread ~ 0.5 mm Does not depend on beam size. ~ 3 hours at injection plateau M. Kuhn - 10/06/2015

Photomultiplier Saturation at 450 GeV Measurement spread for each high voltage setting For 2500 < profile amplitudes < 7500 (no ADC saturation) Emittance spread per HV setting ≤ 0.5 mm for all planes Does not depend on chosen filter or gain, or beam size Smallest spread at highest voltage  No influence of photomultiplier settings on measured emittance! M. Kuhn - 10/06/2015

Photomultiplier Saturation at 6.5 TeV The photomultipliers accumulate a lot of light at 6.5 TeV Only possible gain and filter settings and flattop: Filter ≤ 0.1 % and gain = 1000 V – 1200 V At ~ 1000 V the photomultipliers might enter the non-linear regime Possible solutions: Exchange a filter for an even higher filter (0.2 %  0.02 %)  Saw no improvement Shield photomultipliers  Move location of photomultipliers To be discussed Filter No filter 20 % 10 % 2 % 1 % 0.02 % 0.1 % No transmission M. Kuhn - 10/06/2015

Emittances during the LHC Cycle Large emittance spread at 6.5 TeV! Looks worse for beam 2. Fill 3809 (June 1, 2015), ~ 1 x 1011 ppb, nominal optics, average in/out scan M. Kuhn - 10/06/2015

Measurement Precision Large scan to scan emittance spread Larger at 6.5 TeV than at 450 GeV – start to get noisier during the ramp already Independent of absolute emittance Difficult to tell emittance at 6.5 TeV Very similar for all planes – but seems worse for beam 2 Cannot be explained by wire scanner calibration Verified with orbit bumps and PM saturation studies Cannot be explained by machine settings or beam quality Orbit, tune, coupling, etc. are all set up correctly No intensity losses etc. Calibration of the BSRT with the wire scanners at 6.5 TeV will be very difficult with this large measurement uncertainty! M. Kuhn - 10/06/2015

Comparison with Run 1 Emittances Wire scans during the 2012 LHC cycle Better measurement resolution during the cycle! What could cause the emittance spread at 6.5 TeV in 2015? M. Kuhn - 10/06/2015

Transverse Profiles Run 2 Run 2 6.5 TeV 450 GeV #points to fit at flattop does not change, quality of the profiles looks similar! Run 1 450 GeV Run 1 4 TeV M. Kuhn - 10/06/2015

Combined Profiles at Flattop Energy Trying to overlay profiles at flattop energy to gain accuracy Overlay ~ 10 profiles scanned in ~ 10 min Worked well in Run 1 Difficult in Run 2 Run 1 4 TeV Fill 3809 (June 1, 2015) Run 2 6.5 TeV M. Kuhn - 10/06/2015

Profile Mean Position at 6.5 TeV At 6.5 TeV flattop energy we see large variations of the profile mean position Similar for all planes and independent of beam size In and out scan mean position is not the same! The deviation of mean positions is very large! M. Kuhn - 10/06/2015

Profile Mean Position at 6.5 TeV IN OUT Effect on orbit bump calibration results? OUT IN M. Kuhn - 10/06/2015

Profile Mean Position at 450 GeV Can deviation in mean profile position really have an effect on beam size? 6.5 TeV Same y-scale for injection and flattop energy (also in the other planes). M. Kuhn - 10/06/2015

Residuals Comparison of residuals at 450 GeV and 6.5 TeV All planes look similar, same y-scale Example: B2V1, Fill 3809, June1, 2015 Position [mm] Profile – fit [a.u.] 450 GeV Tales at 450 GeV visible. Otherwise residuals look ok. Position [mm] Profile – fit [a.u.] 6.5 TeV M. Kuhn - 10/06/2015

Average In-Out Scan Is it feasible to average over in and out scan? YES! The difference of in and out scan is added to the error bars. M. Kuhn - 10/06/2015

Average Emittance at 6.5 TeV Average emittance of 4 scans at flattop energy for more accuracy Error from averaging is included in the error bars Before: scan-by-scan emittances After: average emittances Resolution sufficient to measure emittance evolution M. Kuhn - 10/06/2015

Emittances during the Ramp Measured optics during the ramp needed! Fill 3809 (June 1, 2015), ~ 1 x 1011 ppb, nominal optics, average in/out scan M. Kuhn - 10/06/2015

Summary During LHC commissioning we completed: Outstanding: Wire scanner orbit bump calibration at 450 GeV and 6.5 TeV Photomultiplier saturation studies at 450 GeV and 6.5 TeV Emittance measurements during the LHC cycle K-modulation at 450 GeV in point 4 Outstanding: BSRT (cross-) calibration Measurements during collisions – preferably with LHCb SMOG on To cross check absolute emittance measurement K-modulation at 6.5 TeV: point 4 and b* Wire scanner calibration performed only with the 4 operational scanners We will not change systems during TS1 M. Kuhn - 10/06/2015

Conclusion Wire scanner thresholds: 144 bunches per beam at 450 GeV 2.3 x 1011 protons per beam at 6.5 TeV Wire scanner orbit bump calibration shows large uncertainty of position measurement in the vertical planes Preliminary: 4 % error for B1V and 7 % error for B2V We detected no photomultiplier saturation for wire scans of individual bunches For 2500 < profile amplitudes < 7500 Recommend highest possible voltage for small emittance spread Checks to be repeated for 144 bunches if possible Cause of scan to scan emittance spread at higher energies not found yet All fits and profiles look good Solution for now: average several scans for better results M. Kuhn - 10/06/2015

More Plots... M. Kuhn - 10/06/2015

Photomultiplier Saturation at 450 GeV M. Kuhn - 10/06/2015

Fitted Emittance Growth at 450 GeV M. Kuhn - 10/06/2015

Emittance minus Growth M. Kuhn - 10/06/2015

Photomultiplier Saturation at 450 GeV M. Kuhn - 10/06/2015

Photomultiplier Saturation at 6.5 TeV M. Kuhn - 10/06/2015

Residuals at 450 GeV M. Kuhn - 10/06/2015

Residuals at 6.5 TeV M. Kuhn - 10/06/2015

In Out Scans Fill 3809 M. Kuhn - 10/06/2015

Emittances Beam 1 at 6.5 TeV M. Kuhn - 10/06/2015

Emittances Beam 2 at 6.5 TeV M. Kuhn - 10/06/2015

Conclusion Optimal settings for wire scans of individual bunches ( < 6): To be repeated for 144 bunches if possible We detected no photomultiplier saturation Source of noisy scans at higher energies not found yet All fits and profiles are good Wire scanner Injection energy Flattop energy B1H B1V B2H B2V M. Kuhn - 10/06/2015