1. Collimation qualification during the first weeks of the 2011 run
D. Wollmann
R. Assmann, R. Bruce, F. Burkart, M. Cauchi,
D. Deboy, S. Redaelli, A. Rossi, G. Valentino,
Collimation Working Group,
Thanks also to
J. Wenninger,
A. Masi + STI team
Collimation Working Group

2. Outline Beam based setup and qualification of the collimation system
Collimation Settings 2011
Cleaning inefficiencies 2011 (Inj., Collision)
Hierarchy problems at Injection after Technical Stop and Power cut
What happened?
Hypothesis for meta stable loss maps in B1h after power cut
Conclusion
Daniel Wollmann

3. LHC Collimators 44/43 collimators per beam installed in the LHC ring
for multi-turn cleaning, passive protection, injection and dump protection
Advanced Collimator fixed status display (available in the CCC and online)
Modifications to the previous version of E. Veyrune done by G. Valentino  G. Valentino
Daniel Wollmann

4. Beam based setup and qualification of collimation system
Centre collimator jaws around beam  G. Valentino
Determine local beam size at collimators  G. Valentino
Set up system with agreed collimator settings for 2011 (1.5m/10m/1.5m/3m)
Check cleaning efficiency
β-tron losses by crossing a third integer tune resonance (B1-h, B1-v, B2-h, B2-v)
Momentum losses by changing the RF frequency (± 1000 Hz, B1+B2). 1000Hz to make sure that full beam is lost with off-momentum error. Could use smaller.
Daniel Wollmann

5. Collimator Settings Injection optics Squeezed optics Energy [GeV] 450
3500
Primary cut IR7 (H, V, S) [σ]
5.7
Secondary cut IR7 (H, V, S) [σ]
6.7
8.8
Quaternary cut IR7 (H, V) [σ]
10.0
17.7
Primary cut IR3 (H) [σ]
8.0 12
Secondary cut IR3 (H) [σ]
9.3
15.6
Quaternary cut IR3 (H, V) [σ]
17.6
Tertiary cut exp. (H, V) [σ] 13 26
11.8/26/11.8/11.8
TCSG/TCDQ IR6 (H) [σ]
7/8
9.3/9.8
Collimators are driven by functions during the ramp, squeeze and collapsing the separation bumps.
Beam based setups performed (Injection) and (3.5 TeV)
Daniel Wollmann

6. Cleaning inefficiency at Collision since June 2010
Leakage during betatron losses into Q8 of IR7 DS
< 6.1e-4
2011
Daniel Wollmann

7. Cleaning inefficiency at 450 GeV since May 2010
Sudden increase in B1h after TS
Leakage during betatron losses into cold aperture
< 1e-3
2011
Daniel Wollmann

8. What Happened State 1: before TS, all fine, no abnormal observations.
During TS: Realignment of three collimators with large angles (see LMC report from 9.3.). Completely uncorrelated with hierarchy.
Affected collimators: TCSG.A5L3.B2, TCLA.A7R7.B1, TCTH.4L2.B1
State 2: Saturday after TS (only change: solenoids off)
abnormal collimation at 450 GeV for beam 1 horizontal
Fixed by re-setup of skew collimators on Sunday, all normal again
Sunday evening: Power cut. Lost UPS. Need to reset collimation references.
State 3: Tuesday, 03:50 – again abnormal collimation B1 H
State 4: Tuesday, 04:29 – back to normal after re-driving collimators and correcting the orbit.
Daniel Wollmann

9. How it Should Look Like: B1H at injection, So. Afternoon
IR7
Qualification for new settings in B1
IR6
IR3
TCTH L8: < 4e-5
Daniel Wollmann

10. How it Should Look Like (IR7/8): B1H at injection, So. Afternoon
TCSG.D5L7: ~0.026
Skew
Hierarchy OK after re-setup of the 8 skew collimators in IR7 of B1
TCTH L8: ~ 3.2e-5
DS < 2e-4
Daniel Wollmann

11. Problem: B1H at injection, Tue Morning
IR7 hierarchy
TCLAs: ~4e-3
TCTH L8: ~ 8.4e-3
Qualification for new settings in B1
Daniel Wollmann

12. Zoom IR7-IR8 Problem: B1H injection, Tue Morning
TCSGs: ~0.7
Skew
TCTH L8: ~ 8.4e-3
factor 260 times higher losses into IR8!
DS < 6e-5
Daniel Wollmann

13. Why Did We Loose Hierarchy for B1H after TS with Solenoids Off?
A priori unknown. From re-setup:
Collimator centers reproduced within smaller than 80 mm. OK.
Two gaps for skew collimators closed by 13% and 14 %  change of beta beat by 25 – 30%?
Beta beat measurement (Monday morning):
No indication for large beta beat change at injection.
Coupling. Discussed with Massimo, Rogelio, …
coupling can be a source of beam size variation if transverse emittances are not equal.
Rogelio: “I would conclude that coupling is not a likely source of 10% beam size variations under usual conditions (emittances within 20%) because coupling is always well corrected.”
Conclusion: Not understood but fixed.
R. Assmann, D. Wollmann

14. Power Cut: Some Collimators had to be Reset with Positions Sensors
Sunday evening: 2 power cuts on IR7 collimators. UPS power exhausted after 1.5h. Recovery procedure…
Usually, position sensors (LVDT’s) on collimators used for checking, never for setting positions.
Motors and resolvers are initialized with calibration to mechanical stops.
Now we lost this initialization (power + UPS lost).
Full re-calibration too lengthy and would require new beam-based setup afterwards. Solution: use as much as possible resolver history but for some had to use LVDT’s.
Movement of collimator reference.
Collimators
Position update with LVDT or RESOLVER
TCLA.A7L7.B2
Resolver
TCLA.D6L7.B2
TCLA.C6L7.B2
TCP.D6L7.B1
TCP.C6L7.B1
LVDT
TCP.B6L7.B1
TCLA.B6L7.B2
TCSG.A6L7.B1
TCLA.A6L7.B2
TCSG.6L7.B2
TCSG.E5L7.B2
TCSG.D5L7.B2
TCSG.B5L7.B1
TCSG.A5L7.B1
TCSG.B5L7.B2
TCSG.D4L7.B1
TCSG.A4L7.B2
TCSG.B4L7.B1
TCSG.A4L7.B1
TCSG.A4R7.B1
TCSG.A4R7.B2
TCSG.B4R7.B2
TCSG.D4R7.B2
TCSG.B5R7.B1
TCSG.A5R7.B2
TCSG.B5R7.B2
TCSG.D5R7.B1
TCSG.E5R7.B1
TCSG.6R7.B1
TCLA.A6R7.B1
TCSG.A6R7.B2
TCLA.B6R7.B1
TCP.B6R7.B2
TCP.C6R7.B2
TCP.D6R7.B2
TCLA.C6R7.B1
TCLA.D6R7.B1
TCLA.A7R7.B1
A. Masi
R. Assmann, D. Wollmann

15. Effect of Power Cut
A. Masi analysis: average change 19 mm maximum change 102 mm
Independently checked by R. Bruce:
OK but up to 100 mm margin lost:
~0.1 s at 450 GeV (out of 1 s)
0.3 s at 3.5 TeV (out of 2.8 s)
Would be unacceptable for 7 TeV or tight collimator settings at
3.5 TeV.
As we see long power cuts, this requires improvements in the collimator protection against these events.
50 mm
R. Bruce
R. Assmann, D. Wollmann

16. “Bad” and “Good” Loss Map within 1 Hour
03:50: “Bad” loss map for beam 1 horizontal
04:29: “Good” loss map for beam 1 horizontal, after re-driving collimators and orbit correction.
Hypothesis 1: Collimators not correctly positioned for 03:50.
Checked by A. Masi: Difference < 14 mm, but beam 2. beam 1 below 10 mm.
Checked by G. Valentino: Largest difference 4 mm for beam 1.
Hypothesis 2: Coupling.
Checked with loss map but no effect.
Hypothesis 3: Orbit difference.
Nothing beyond ± 150 mm in IR7 visible in orbit plots from Joerg.
However, new issue with filling-pattern dependent BPM readings!  Joerg
Most likely cause of meta-stable loss maps: Orbit changes due to BPM systematics and correction strategy.
R. Assmann, D. Wollmann

17. Visible Orbit Structure in IR7 (with respect to situation during collimation setup for 450 GeV)
Not just an offset (filling pattern systematics in BPM’s) but also some unexplained structure built up since 26.2.
“Good” Lossmap 2
“Bad” Lossmap 1
Courtesy J. Wenninger
R. Assmann, D. Wollmann

18. Conclusion
Local cleaning inefficiency compares well to experiences from 2010
Re-setup of skew collimators in B1-IR7 cured hierarchy problem after TS
Improve collimator system stability against long power cuts.
Propose not to re-setup collimation after the recent power cut:
Significant but still acceptable effects. Not source of the “hierarchy” problem.
Orbit issue must be sorted out first (to what reference do we set up)!
Problem found by chance (measure regularly). If the orbit is corrected to standard reference, we found the last days “good” loss maps (with 1 nominal bunch):
However, new orbit measurement systematics with filling pattern:
Measured orbit change is corrected away  specify maximum size
Then give impact on collimation (efficiency and passive protection)
Orbit correction with many bunches, but then loss map with 1 bunch?
Recovery for 75 ns physics: revisit changes done in skew collimators after TS in IR7.
R. Assmann, D. Wollmann