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Update on ALICE background and TDI pressure

Update on ALICE background and TDI pressure . A. Alici (INFN), A. Di Mauro (CERN) LBS #40, 17/09/2012. Introduction.

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Update on ALICE background and TDI pressure

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  1. Update on ALICE background and TDI pressure A. Alici (INFN), A. Di Mauro (CERN) LBS #40, 17/09/2012

  2. Introduction • Since July 27 a new injection sequence (fill B1 and B2 up to ~1.0E14 p, then pause B2 and complete B1) has been adopted to mitigate vacuum degradation in TDI.4L2. This choice was driven by the observation that: • above ~ 1E14 p in both beams the pressure increases until the opening of the jaws at the end of B1 injection; • the larger the P increase during injection the longer the recovery time is. • That injection procedure allowed to minimize the pressure spikes observed in TDI at the end of injection; it worked in a large fraction of the fills. However, since ~ Aug 12 (after the increase of bunch charge) a new behavior of TDI pressure has been observed: the decrease after the initial spike is suddenly followed by a large pressure bump which can last several hours. • Since Sept 4 the separated injection of first B1 followed by B2 is under test to minimize the duration of B1 injection. • As a reminder, ALICE cannot ramp up most of gaseous detectors when the TDI P is larger than ~ 3E-8 mbar, corresponding to bkgd contamination up to 50% (depending on luminosity); ideal operating conditions would be P < 7E-9 mbar LBS#40

  3. TDI P overview in August step in beam intensity LBS#40

  4. TDI P overview in August step in beam intensity 3E-8 Monotonous decrease after initial spike Bump following decrease LBS#40

  5. TDI P overview in August 3E-8 Large P bump , most of fill duration TDI P > 3E-8 mbar LBS#40

  6. FILL 2984 before RAMP Last injections of B1 delayed, some P increase LBS#40

  7. FILL 2984 P bump after initial decrease: 6 h lost LBS#40

  8. FILL 2991 before RAMP Another example of not perfect “modified injection” LBS#40

  9. FILL 2991 P bump after initial decrease: 4 h lost LBS#40

  10. FILL 2992 before RAMP A nice injection example, P ~ 3E-8 mbar LBS#40

  11. FILL 2992 Very limited P bump LBS#40

  12. FILL 2997 before RAMP Last injections of B1 delayed, some P increase LBS#40

  13. FILL 2997 Large P bump: 6 h, no data taking at all LBS#40

  14. FILL 3002 before RAMP A good example of modified injection, P ~ 3E-8 mbar LBS#40

  15. FILL 3002 Very limited P bump As in FILL 2992, if P after injection is below 3E-8 mbar the P bump does not exceed this value LBS#40

  16. FILL 3009 before RAMP When injecting only B1 P stays below ~ 2 E-8 mbar -> test B1 and B2 separated injections LBS#40

  17. TDI P overview in September Since 04/09: B1 injected before B2 3E-8 TDI P almost always below 3E-8 mbar, shorter recovery time but exceptions are always possible LBS#40

  18. FILL 3027 before RAMP LBS#40

  19. FILL 3027 Start data taking at SB declaration !! LBS#40

  20. FILL 3032 before RAMP LBS#40

  21. FILL 3032 LBS#40

  22. TDI P “cumulative” effect How to explain the exceptions…. FILL 3035 FILL 3034 FILL 3036 When interval between subsequent fills is short, TDI P cannot recover and adds to next fill P LBS#40

  23. FILL 3035 before ramp 6E-8! P already above 1E-8 mbar Some hesitations during B1 injection LBS#40

  24. FILL 3036 before ramp 5E-8! P already at ~2E-8 mbar Nice injection but… LBS#40

  25. FILL 3071 before ramp P starts increasing when both beams are above 1e14 p LBS#40

  26. FILL 3071 LBS#40

  27. Overall vacuum in August TDI ID800 VGPB.120 VGPB.623 Left LSS2 Right LSS2, good vacuum condition VGPB.623 ID800 VGPB.120 After polarity reversal ID800 vacuum improved a lot LBS#40

  28. Overall vacuum in September TDI ID800 VGPB.120 VGPB.623 Left LSS2 Right LSS2, good vacuum condition VGPB.623 ID800 VGPB.120 LBS#40

  29. L-side vacuum FILL 2981 FILL 2976 TDI drives pressure in close sections (ID800, VGPB.120) LBS#40

  30. L-side vacuum FILL 2984 FILL 2983 TDI drives pressure in close sections (ID800, VGPB.120) LBS#40

  31. TDI Position Sensors: LVDT • One LVDT on each side of the support bar allows to detect deformation Beam 900 mm 2200 mm 900 mm DOWN UP Jaw 2 1 2 1 Motor Motor From C. Bracco’s slides at MPP, 14/09/12 LBS#40

  32. TDI Position Sensors: LVDT • One LVDT on each side of the support bar allows to detect deformation Beam 900 mm 2200 mm 900 mm Jaw DOWN UP 2 1 2 1 Motor Motor Junction which allows for some expansion without deformation From C. Bracco’s slides at MPP, 14/09/12 LBS#40

  33. FILL 2505 I~ 8.3E13 p, TDI P <1E-8 mbar, LVDT variation ~ 10um LBS#40

  34. FILL 3021 I~ 2.1E14 p, TDI P ~4E-8 mbar, LVDT variation ~ 12um LBS#40

  35. FILL 3036 I~ 2.1E14 p, TDI P ~5E-8 mbar, LVDT variation ~ 13um LBS#40

  36. Offline checks: BkgdvsLumi Run 186003, 01/08/2012 BG/ALL ~ 0.13 (L = 1.6 Hz/cm2) BG/((ALL-BG)*L0/L + BG) ~ 0.2 normalized at L0 = 1Hz/cm2 beam-bkgd side A (Left) beam-bkgd side C (Right) LBS#40

  37. Offline checks: BkgdvsLumi Run 188025, 09/09/2012 BG/ALL ~ 0.53 (L = 0.36 Hz/cm2) BG/((ALL-BG)*L0/L + BG) ~ 0.29 normalized at L0 = 1Hz/cm2 beam-bkgd side A (Left) beam-bkgd side C (Right) LBS#40

  38. Offline checks: BkgdvsLumi Run 188028, 09/09/2012 BG/ALL ~ 0.5 (L = 0.21 Hz/cm2) BG/((ALL-BG)*L0/L + BG) ~ 0.17 normalized at L0 = 1Hz/cm2 beam-bkgd side A (Left) beam-bkgd side C (Right) LBS#40

  39. ALICE luminosity in Jul-Aug ALICE Online Integrated luminosity in 2012 = 2.75 pb-1 recorded luminosity = 1.95 pb-1 (71%) July luminosity issues August new injection procedure since 26/07 31 32 33 34 35 week 35 0.11 pb-1 delivered 0.08 pb-1 recorded e = 72% week 34 0.2 pb-1 delivered 0.15 pb-1 recorded e = 75% week 32 0.08 pb-1 delivered 0.06 pb-1 recorded e = 78% week 33 0.06 pb-1 delivered 0.04 pb-1 recorded e = 58% week 31 0.41 pb-1 delivered 0.21 pb-1 recorded e = 50% LBS#40

  40. ALICE luminosity in Jul-Aug lumi scans again low luminosity, maybe due to abort gap cleaning fill 2929 (8/08) ALICE target luminosity Since the 8th of August and for more than 10 days LHC was not able to deliver to ALICE luminosities higher than 0.6Hz/cm2.The reason: very poor satellite population . LBS#40

  41. Conclusions • Separated injection of B1 and B2 allows to mitigate vacuum degradation in TDI • TDI P large bumps still observed when injection is longer • Correlation with heating (jaws deformation) to be further studied • After ALICE magnets polarity reversal (and increase of crossing angle) P spikes in ID800.R2 disappeared • Incidence of bkgd on quality of data taking is clearly also related to the delivered luminosity LBS#40

  42. BACKUP SLIDES LBS#40

  43. ALICE vacuum layout A C A side 70 m 69.7 m VGPB.623.4L2 VGI.500.4L2 120m C side 70 m 69.7 m VGPB.623.4R2 VGI.500.4R2 120m LBS#40 43

  44. ALICE layout Beam 1 BCM-A 8 sensors z = + 6 m, r = 10 cm Beam 2 BCM C 7 sensors z = -18.5 m, r=10 cm LBS#40 44

  45. The V0 detector ITS V0A rin=8 cm rout=100 cm V0C rin=8 cm rout= 76 cm SPD V0C V0A 340 cm 90 cm Two arrays of scintillator counters (V0A and V0C). Time spectra allow beam-gas events rejection LBS#40 45

  46. V0 timing properties V0A V0C IP beam2 beam1 340cm ~11.3ns 90cm ~3ns V0A+V0C ≈ 14.3ns V0A-V0C ≈ 8.3ns collisions IP beam1 Beam background from beam2 ~-11.3ns ~3ns V0A+V0C ≈ -8.3ns V0A-V0C ≈ -14.3ns Bkgd1 (BGA) Beam background from beam1 IP satellites beam2 ~11.3ns ~-3ns V0A+V0C ≈ 8.3ns V0A-V0C ≈ 14.3ns Bkgd2 (BGC) LBS#40

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