Results of TCL scans D. Mirarchi, M. Deile, S. Redaelli, B. Salvachua, Collimation Working Group, 22 nd February 2016

Introduction End-of-Fill studies performed the 18/9/15 (Fill 4384) Scan of TCL5 and 6 around CMS, for both beams Evaluation of physics debris absorption performance as a function of TCLs aperture Inputs for 2016 settings of TCLs and XRPs 22/02/16CWG, Daniele Mirarchi2

Measurement procedure 3.TCL6 opened in steps of 1  from 25  to 30 , and 2  from 30  to 40 , every 2min 4.TCL5 closed in steps of 2  from 35  to 15 , every 2min (with TCL6 at 40  1min shift between movements in the two beams, to minimise crosstalk 22/02/16CWG, Daniele Mirarchi3 1.Collimation system at 2015 collision settings 2.TCL4 kept at 15 , and TCL5 opened to 35 

Off-line analysis All BLMs from cell 5 to cell 15 (beginning of the ARC) taken into account Beam loss for each step given by mean value in the central minute, and error by the RMS 1.3s running sum used Two main analysis performed: 22/02/16CWG, Daniele Mirarchi4 Recorder losses normalised with respect to measured luminosity at CMS Normalisation w.r.t. CMS luminosity (Useful input for TOTEM on damage level) Further normalisation also to max of losses (Useful input for evaluation of TCL shielding) Time range used

TCL5 scan 22/02/16CWG, Daniele Mirarchi5

Overview of TCL5 scan Shown losses recorded at each step from cell 4 to cell 10 Normalisation also w.r.t. initial losses to have a feeling of the relative variation during the scan 22/02/16CWG, Daniele Mirarchi6 BEAM2BEAM1 gap TCT & TCL4 TCL5 TCL6 Q6 Q7

Overview of TCL5 scan Shown losses recorded at each step from cell 4 to cell 10 Normalisation also w.r.t. initial losses to have a feeling of the relative variation during the scan 22/02/16CWG, Daniele Mirarchi7 BEAM2BEAM1 gap TCT & TCL4 TCL5 TCL6 Q6 Q7

Overview of TCL5 scan Shown losses recorded at each step from cell 4 to cell 10 Normalisation also w.r.t. initial losses to have a feeling of the relative variation during the scan Main observation while closing TCL5: Visible asymmetry between B1 and B2, not yet clear. 22/02/16CWG, Daniele Mirarchi8 BEAM2BEAM1 gap TCT & TCL4 TCL5 TCL6 Q6 Q7 No effect from cell 9 onward Significant increase of losses in cell 5 Significant decrease of losses in cell 6 Modest decrease of losses in cell 7 and 8

Summary of TCL5 scan Average performed for BLMs on the same element, details for each element in the next From 35  to 15  : Increase of a factor ~ 8 and ~ 3 at TCL5 and Q5 Decrease of a factor ~ 5 and ~ 3 at TCL6 and Q6 Decrease of a factor ~ 1.5 at Q7 Decrease of a factor ~ 2.5 at Q8, from 23  Increase of a factor ~ 5 and ~ 2 at TCL5 and Q5 Decrease of a factor ~ 5 and ~ 3 on TCL6 and Q6 Small impact on Q7 and Q8 (factor ~ 1.5 and ~ 1.2) 22/02/16CWG, Daniele Mirarchi9 BEAM1BEAM2 Norm. Lumi. Norm. max

Loss on Q5 during TCL5 scan Highest absolute losses and variations at the entrance of the element. Smallest absolute losses and variations in the middle of the element. 22/02/16CWG, Daniele Mirarchi10 Norm. Lumi. Norm. max BEAM1BEAM2

Loss on Q6 during TCL5 scan 22/02/16CWG, Daniele Mirarchi11 Norm. Lumi. Norm. max BEAM1BEAM2 Very similar to Q5, but of course the trend is the opposite Loss behaviour at the exit of Q6 for B2 differ significantly from B1, very similar to entrance of Q7 (next)

Loss on Q7 during TCL5 scan 22/02/16CWG, Daniele Mirarchi12 Norm. Lumi. Norm. max BEAM1BEAM2 Difference between reductions at entrance and exit of the element starts to increase Also the difference between the two beams becomes more significant

Loss on Q8 during TCL5 scan Very different loss behaviour between entrance and exit of Q8 22/02/16CWG, Daniele Mirarchi13 Norm. Lumi. Norm. max BEAM1BEAM2 Losses at the exit of the element are for the first time higher than at the entrance Significant difference between the two beams

Loss on XRP during TCL5 scan Significantly different level of absolute losses in the two beams Interesting pattern in both beams at XRP.C & D showing a ”balancing” of the two main loss contribution. 22/02/16CWG, Daniele Mirarchi14 Norm. Lumi. Norm. max BEAM1BEAM2 Possible explanation: loss increase until ~ 19  (B1) due to larger exposition to the physics debris, and than decreases due to the reduced showering due to the TCL itself because of the reduced debris intercepted.

TCL6 scan 22/02/16CWG, Daniele Mirarchi15

Overview of TCL6 scan 22/02/16CWG, Daniele Mirarchi16 Shown losses recorded at each step from cell 4 to cell 10 Normalisation also w.r.t. initial losses to have a feeling of the relative variation during the scan BEAM2BEAM1 gap TCT & TCL4 TCL5 TCL6 Q8 Q7 Q9 Q8

Overview of TCL6 scan 22/02/16CWG, Daniele Mirarchi17 Shown losses recorded at each step from cell 4 to cell 10 Normalisation also w.r.t. initial losses to have a feeling of the relative variation during the scan BEAM2BEAM1 gap TCT & TCL4 TCL5 TCL6 Q8 Q7 Q9 Q8

Overview of TCL6 scan Visible asymmetry between B1 and B2, not yet clear. 22/02/16CWG, Daniele Mirarchi18 Shown losses recorded at each step from cell 4 to cell 10 Normalisation also w.r.t. initial losses to have a feeling of the relative variation during the scan BEAM2BEAM1 gap TCT & TCL4 TCL5 TCL6 Q8 Q7 Q9 Q8 Main observation while opening TCL6: Increase of losses only between MBA-MBB in cell 9 (B2) Modest increase of losses at MBA and MBB in cell 8 (B1) Increase of losses at Q8 (B1)

Summary of TCL6 scan Very modest effect on losses at TCL6, Q6 and Q7 Relatively linear decrease of a factor ~2 on Q8 Very modest effect on all the elements 22/02/16CWG, Daniele Mirarchi19 Average performed for BLMs on the same element, details for each element in the next BEAM1BEAM2 Norm. Lumi. Norm. max From 42  to 26  : Much less interesting scan due to the large minimum gap of the scan

Loss on Q8 during TCL6 scan 22/02/16CWG, Daniele Mirarchi20 Norm. Lumi. Norm. max BEAM1BEAM2 Largest loss excursions observed, same analysis for the other elements in backup (reductions <20%) Significant difference between the two beams

Loss on XRP during TCL6 scan Significantly different level of absolute losses in the two beams Interesting decrease of losses observed only on XRP.B (closest to TCL6) probably do to reduced backscattering from TCL6 22/02/16CWG, Daniele Mirarchi21 Norm. Lumi. Norm. max BEAM1BEAM2

Why these differences between beams and TCLs? 22/02/16CWG, Daniele Mirarchi22

Why this asymmetry of losses? Checked single pass (starting from IP5) and periodic dispersion, plus orbit: 22/02/16CWG, Daniele Mirarchi23 Q7Q9 Q8 TCL4 TCL5 TCL6 Q7Q9 Q8 TCL4 TCL5 TCL6 Single pass dispersionPeriodic dispersion Single pass dispersion identical for both beams: asymmetry not explained Periodic dispersion shows that off-momentum particles undergoing multi-turn are shifted toward the centre of the beam pipe Such particles should be lost in IR3 Still hard to explain the asymmetry observed Reference system of Beam 2: used Beam 4 in MADX (right-hand)

Q7Q9 Q8 TCL4 TCL5 TCL6 Main optics difference TCL5-TCL6 Checked the phase advance w.r.t. IP5: 22/02/16CWG, Daniele Mirarchi24 Different phase advance of TCL5 ( ~ 90deg) and TCL6 ( ~ 163deg) from IP5 gives an indication on the different efficiency in angular cut performed (for same setting in  ) on physics debris Using:  Considering protons scattered at 0 betatron amplitude and both TCLs at 15 , the angular cut performed is: 1.2  rad and 0.3  rad by TCL6 and TCL5, respectively  Equivalent cut in angle w.r.t. TCL5 at 15  achieved with TCL6 at 4.5  Just rough numbers to give an idea

Conclusions Scans of TCL5 and 6 around CMS, for both beams in collisions carried out as EoF (fill 4384) Significant increase of losses in cell 5 Significant decrease of losses in cell 6 Modest decrease of losses in cell 7 and 8 No effect from cell 9 onward Visible asymmetry between B1 and B2, not yet clear. Interesting pattern present in both beam at XRP.C & D that shows the ”balancing” of the two main loss contribution. Increase of losses only between MBA-MBB in cell 9 for B2 Modest increase of losses on MBA, MBB and MQ in cell 8 for B1 Visible asymmetry between B1 and B2, not yet clear. Interesting decrease of losses observed only on XRP.B (closest to TCL6) probably do to reduced backscattering from TCL6 Important to repeat these scans in 2016, also with deeper insertion of TCL6 22/02/16CWG, Daniele Mirarchi25 Main empirical results obtained with scans of TCL5 from 35  to 15  : Scans of TCL6 from 25  to 42  :