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UFOs in the LHC

UFOs in the LHC. Tobias Baer LBOC June, 14 th 2011. Acknowledgements : N. Garrel , B. Goddard, E. B. Holzer, S. Jackson, M. Misiowiec , E. Nebot, A. Nordt, J. Uythoven, J. Wenninger, C. Zamantzas. Content. Content. UFO Dumps. 18 beam dumps due to UFOs in 2010.

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UFOs in the LHC

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  1. UFOs in the LHC • Tobias Baer • LBOC June, 14th 2011 Acknowledgements: N. Garrel, B. Goddard, E.B. Holzer, S. Jackson, M. Misiowiec, E. Nebot, A. Nordt, J. Uythoven, J. Wenninger, C. Zamantzas

  2. Content

  3. Content

  4. UFO Dumps • 18 beam dumps due to UFOs in 2010. • UFOs are fast beam losses (loss duration some 10 turns) • UFOs occur often at unconventional loss locations (e.g. in the arc) • 11 beam dumps due to UFOs in 2011. • 8 in injection region (2010: 2) • 1 dump at 450 GeV. (6.6.2011)

  5. Content

  6. UFOs Detection in 2011 • 2010: 113 UFOs below threshold found in logging database. (E. Nebot) • 2011: Online UFO detection from live BLM data.Losses (RS 4) of two BLMs in 40m are above 1E-4 Gy/s.RS 2 / RS 1 > 0.55 (UFO average : 0.89). RS 3 / RS 2 > 0.45 (UFO average: 0.79). • Over 8000 triggers so far. • From subset of about 300 manually verified triggers: About 65% are UFOs, 15% ambiguous cases, 20% are false triggers. • For most analysis additional cut. E.g.: Only flat top UFOs, loss of UFO BLM (RS05) > 2∙10-4Gy/s (≈ 2 ‰ of threshold). 74 events remain of subset, of which 71 are clear UFOs (96%) and 3 are ambiguous cases.

  7. Events Below Threshold • “threshold” = lowest threshold in standard arc cell. • Most events are much below threshold. 628 candidate UFOs at 3.5 TeV. Signal RS05 > 5∙10-4Gy/s. nominal threshold 7 TeV

  8. Spatial UFO Distribution 3.5 TeV1096 candidate UFOs. Signal RS05 > 5∙10-4Gy/s. 450 GeV591 candidate UFOs. Signal RS05 > 5∙10-4Gy/s. The UFOs are distributed all around the machine. About 7% of all UFOs are around the MKIs. 53 candidate UFOs at MKI for Beam 2. gray areas around IRs are excluded from UFO detection. Mainly UFOs around MKIs

  9. UFO Rate in 2011 • On average: 10 UFOs/hour 1904 candidate UFOs during stable beams. Signal RS05 > 2∙10-4Gy/s. Data scaled with 1.76 (detection efficiency from reference data) 1092b 144 bpi 1092b 108 bpi 768b 72 bpi 480b 72 bpi 228 b 36 bpi 768b 72 bpi 336b 72 bpi 336b 72 bpi 480b 36 bpi 336b 36 bpi 228 b 36 bpi 480b 36 bpi 480b 72 bpi 624b 72 bpi 768b 108 bpi 912b 108 bpi

  10. Peak Signal courtesy ofE. Nebot • No clear dependency of peak loss on intensity. (cf. E.B. Holzer at Evian Dec. 2010) • No clear dependency of peak loss on bunch intensity.

  11. Loss Duration • Tloss: Given by fitting single function (Gaussian up to t=Tloss, 1/t afterwards) to data. • Loss duration: UFOs have the tendency to become faster with increasing intensity. (cf. E.B. Holzer at Evian Dec. 2010) courtesy ofE. Nebot

  12. Peak Signal vs Loss Duration • Tendency that harder UFOs are faster. courtesy ofE. Nebot

  13. Content

  14. Beam dump on 6.6.2011 • UFO at MKI in Pt. 2, at 450 GeV. TCT MKIs

  15. Beam dump 06.06.2011 • From fit to losses (BLMEI.05L2.B1E10_MKI.D5L2.B1): • Amplitude: 7.73 Gy/s (Threshold: 2.3 Gy/s) • Width: 0.77 ms resulting speed of transiting dust particle = 0.47 m/s.(assuming ϵn=2.2µm·rad) (cf. T. Baer 86th LMC)

  16. Peak Losses • Peak loss for MKI UFOs at 450 GeV. • Threshold (RS1 = 2.3 Gy/s) 336 candidate UFOs at 450 GeV. Signal RS01 > 2∙10-4Gy/s. + 1 event with 3.5Gy/s (dump 06.06.2011)

  17. UFOs around Injection Region • 679 UFOs around the MKIs caused 9 beam dumps. • Most of the UFOs around the MKIs occur before going tostable beams.

  18. MKI UFOs DuringScrubbing • Typicalscenariofor MKI UFOs duringscrubbing: Loss spikes occur in first few minutes after an injection and go away then. 2 hours

  19. UFOs at MKIs per fill • Flashover of MKI D Pt.8 before Fill 1721 (vacuum valves moved in). Fill 1721: 21 MKI UFOs in Pt.8 2 MKI UFOs in Pt.2 Flashover

  20. Correlation with Vacuum • Despite a large vacuum spike, there is no clear correlation with UFOs

  21. UFOs at MKIs • 08.04. – 05.05. in total 460fast loss events around MKIs. (104 around MKI in IP2, 336 around MKI in IP8). • Distribution of first BLM which sees the loss: Beam direction Beam direction Right of IP8 Left of IP2

  22. Content

  23. Next Steps • Improve diagnostics. Acquisition of BLM Study Buffer for UFO events. Successful test during technical stop. • Better localization of MKI UFOs. Additional BLMs during next Technical Stop. • MD on MKI UFOs. • Better understanding of Quench Limit. • Additional Simulations (F. Zimmermann, Y. Levinsen) • Mitigation: Further increase of BLM thresholds...But: For higher energies thresholds need to be decreased.

  24. Summary • 11 UFO related beam dumps in 2011 so far (18 in 2010). • Over 5000 UFOs below dump threshold detected in 2011 so far.Most events at 3.5 TeV. UFO rate constant at 10 UFOs/hour at 3.5 TeV. • Many UFOs around injection kicker magnetsDuring scrubbing: increased UFO rate after each injection. Increased UFO rate after MKI Flashover. • Next steps: UFO MD, Improve the diagnostics, better understanding of quench limits, learn from simulations.

  25. Thank you • for your Attention • Tobias Baer • CERN BE/OP • Tobias.Baer@cern.ch • Office: +41 22 76 75379 • Further information: • T. Baer, “UFOs in the LHC”, Joint DESY and University of Hamburg Accelerator Physics Seminar, May 2011. • J. Wenninger, “Analysis attempt of dump UFOs”, LHC Machine Protection Panel, Geneva, March 2011. • M. Sapinski, “Is the BLM system ready to go to higher intensities?”, Workshop on LHC Performance, Chamonix, Jan. 2011. • E.B. Holzer, “Losses away from collimators: statistics and extrapolation”, LHC Beam Operation Workshop, Evian, Dec. 2010.

  26. Backup slides

  27. UFOs in 2010 • 18 beam dumps due to UFOs. (since 07.07.2010) • 113 UFOs below threshold found in logging database. (E. Nebot)(03.08.2010 - 28.10.2010) • UFO rate proportional to intensity. • No dependency of peak signal on intensity. (cf. E.B. Holzer at Evian Dec. 2010) • Loss duration has tendency to become faster with higher intensity. (cf. E.B. Holzer at Evian Dec. 2010) J. Wenninger

  28. Event Rate • 113 events below threshold found in 2010. (E. Nebot) • UFO rate: proportional tobeam intensity. courtesy ofE. Nebot

  29. Calibration of Tloss • Correlation of Tloss and width of Gaussian fitted topost mortem turn-by-turn data. courtesy ofE. Nebot

  30. Fast Loss Event Rate • After the increase of the BLM Threshold by a factor of 3 there were about 4.1 times less beam dumps due to fast loss events.

  31. UFO Algorithm • Losses (RS 4) of at least two BLMs within 40m are above 1E-4 Gy/s. • A BLM is not taken into account if It is at a TCT It is in IP3, IP6 or IP7 RS 2 / RS 1 > 0.55 (UFO average : 0.89).RS 3 / RS 2 > 0.45 (UFO average: 0.79). 3. The acquisition is skipped for a few seconds after injection warning and beam wire scan timing event.

  32. LHC UFO Buster • LHC Console Manager -> Fixed Displays -> BLM -> UFO Buster

  33. UFO Detection • For 2010: 113 UFOs below threshold found in logging database. (E. Nebot) • For 2011: Online UFO detection by UFO Buster. Detects UFOs in BLM concentrator data (1Hz). • 5000 UFOs below threshold found so far. • Most events are much below threshold. nominal arc threshold 7 TeV 4905 candidate UFOs at 3.5 TeV. “threshold” = lowest threshold in standard arc cell.

  34. Dump on 01.05.2011 • Dump of BLMQI.04L2.B1E20_MQY on RS 3, 4 and 5 • Dump of BLMQI.04L2.B1E20_MQY on 320µs, 640µs and 2.5ms integration time

  35. Dump on 01.05.2011 • From fit tolosses (BLMEI.05L2.B1E10_MKI.D5L2.B1): Amplitude: 0.63 Gy/s Width: 0.29 ms

  36. Correlation with Vacuum

  37. Dynamics of Dust Particles • From simulations: • Dust particle will be positively ionized and be repelled from the beam. Beam intensity: 2.3∙1012 protons, Al object. • Loss duration of a few ms. Losses become shorter for larger beam intensities. courtesy ofF. Zimmermann

  38. CorrelationwithWire Scanner • Fromwirescans: linear dependencyof BLM signal on beam energy courtesy ofM. Sapinski(cf. Chamonix 2011)

  39. Layout of MKI Region

  40. UFO size • Two extreme cases: • UFO much larger than beam: the beam is imaging the UFO. • UFO much smaller than beam: the UFO is imaging the beam. Most UFO shapes are Gaussian, thus most UFOs are expected to be smaller than the beam. • From FLUKA simulations: size ≈ 1 μm. (cf. M. Sapinski, F. Zimmermann at Chamonix 2011) courtesy ofJ. Wenninger(cf. MPP 25.03.2011)

  41. UFO Speed • UFO speed: • From free fall: • The UFO speed corresponds to the expected speed for a free fall from the aperture. εnorm = 2.5 µm·rad β = 150 m 22 mm free fall vu: UFO speed, σb: transverse beam size, σu: UFO size,σT: temporal width of loss.

  42. Known Dust Particle Sources • Distributed ion pumps (PF-AR, HERA). • Electrical Discharges (PF-AR). • Movable Devices. • Particles frozen or condensated at cold elements. (ANKA)

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