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, 11.04.2011 Thanks also to J. Wenninger, A. Masi + STI team Collimation Working Group 11.04.2011

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

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

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

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 26.-28.02.2011 (Injection) and 06.-11.03.2011 (3.5 TeV) Daniel Wollmann

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

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

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

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

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

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

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

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

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

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

“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

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

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