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

2. 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

3. 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

4. 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

5. 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

6. Orbit Bump Calibration Beam 1
Beam 1 orbit bumps on May 14, 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

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

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

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

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

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

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

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

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

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

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

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

36. 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