UFOs in the LHC Tobias Baer LBOC June
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 June, 14 th 2011 LHC Beam Operation Committee 1
Content June, 14 th 2011 1. UFO Dumps 2. Below Threshold UFOs 3. UFOs at MKIs 4. Outlook LHC Beam Operation Committee 2
Content June, 14 th 2011 1. UFO Dumps 2. Below Threshold UFOs 3. UFOs at MKIs 4. Outlook LHC Beam Operation Committee 3
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 Ge. V. (6. 6. 2011) June, 14 th 2011 LHC Beam Operation Committee 4
Content June, 14 th 2011 1. UFO Dumps 2. Below Threshold UFOs 3. UFOs at MKIs 4. Outlook LHC Beam Operation Committee 5
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 40 m are above 1 E-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 (RS 05) > 2∙ 10 -4 Gy/s (≈ 2 ‰ of threshold). 74 events remain of subset, of which 71 are clear UFOs (96%) and 3 are ambiguous cases. June, 14 th 2011 LHC Beam Operation Committee 6
nominal threshold 7 Te. V Events Below Threshold 628 candidate UFOs at 3. 5 Te. V. Signal RS 05 > 5∙ 10 -4 Gy/s. “threshold” = lowest threshold in standard arc cell. Most events are much below threshold. June, 14 th 2011 LHC Beam Operation Committee 7
Spatial UFO Distribution 3. 5 Te. V 450 Ge. V 1096 candidate UFOs. Signal RS 05 > 5∙ 10 -4 Gy/s. 591 candidate UFOs. Signal RS 05 > 5∙ 10 -4 Gy/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. Mainly UFOs around MKIs gray areas around IRs are excluded from UFO detection. June, 14 th 2011 LHC Beam Operation Committee 8
UFO Rate in 2011 1092 b 144 bpi 1092 b 108 bpi 36 bpi 72 bpi 108 bpi 228 b 480 b 768 b 912 b 768 b 72 bpi 624 b 72 bpi 480 b 72 bpi 336 b 72 bpi 480 b 36 bpi 336 b 36 bpi 228 b 36 bpi 1904 candidate UFOs during stable beams. Signal RS 05 > 2∙ 10 -4 Gy/s. Data scaled with 1. 76 (detection efficiency from reference data) On average: 10 UFOs/hour June, 14 th 2011 LHC Beam Operation Committee 9
Peak Signal courtesy of E. Nebot • No clear dependency of peak loss on intensity. Dec. 2010) (cf. E. B. Holzer at Evian • No clear dependency of peak loss on bunch intensity. June, 14 th 2011 LHC Beam Operation Committee 10
Loss Duration • Tloss: Given by fitting single function (Gaussian up to t=Tloss, 1/t afterwards) to data. • Loss duration: duration UFOs have the tendency to become faster with increasing intensity. Dec. 2010) (cf. E. B. Holzer at Evian courtesy of E. Nebot June, 14 th 2011 LHC Beam Operation Committee 11
Peak Signal vs Loss Duration courtesy of E. Nebot June, 14 th 2011 Tendency that harder UFOs are faster. LHC Beam Operation Committee 12
Content June, 14 th 2011 1. UFO Dumps 2. Below Threshold UFOs 3. UFOs at MKIs 4. Outlook LHC Beam Operation Committee 13
Beam dump on 6. 6. 2011 TCT MKIs UFO at MKI in Pt. 2, at 450 Ge. V. June, 14 th 2011 LHC Beam Operation Committee 14
Beam dump 06. 2011 • From fit to losses (BLMEI. 05 L 2. B 1 E 10_MKI. D 5 L 2. B 1): • 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 86 th LMC) June, 14 th 2011 LHC Beam Operation Committee 15
Peak Losses 336 candidate UFOs at 450 Ge. V. Signal RS 01 > 2∙ 10 -4 Gy/s. + 1 event with 3. 5 Gy/s (dump 06. 2011) Peak loss for MKI UFOs at 450 Ge. V Threshold (RS 1 = 2. 3 Gy/s) June, 14 th 2011 LHC Beam Operation Committee 16
UFOs around Injection Region • 679 UFOs around the MKIs caused 9 beam dumps. Most of the UFOs around the MKIs occur before going to stable beams. June, 14 th 2011 LHC Beam Operation Committee 17
MKI UFOs During Scrubbing • Typical scenario for MKI UFOs during scrubbing: Loss spikes occur in first few minutes after an injection and go away then. 2 hours June, 14 th 2011 LHC Beam Operation Committee 18
UFOs at MKIs per fill Flashover Fill 1721: 21 MKI UFOs in Pt. 8 2 MKI UFOs in Pt. 2 Flashover of MKI D Pt. 8 before Fill 1721 (vacuum valves moved in). June, 14 th 2011 LHC Beam Operation Committee 19
Correlation with Vacuum Despite a large vacuum spike, there is no clear correlation with UFOs June, 14 th 2011 LHC Beam Operation Committee 20
UFOs at MKIs • 08. 04. – 05. in total 460 fast loss events around MKIs. (104 around MKI in IP 2, 336 around MKI in IP 8). Distribution of first BLM which sees the loss: Beam direction Right of IP 8 Left of IP 2 June, 14 th 2011 LHC Beam Operation Committee 21
Content June, 14 th 2011 1. UFO Dumps 2. Below Threshold UFOs 3. UFOs at MKIs 4. Outlook LHC Beam Operation Committee 22
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. June, 14 2011 LHC Beam Operation Committee • th 23
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 Te. V. UFO rate constant at 10 UFOs/hour at 3. 5 Te. V. • Many UFOs around injection kicker magnets During scrubbing: increased UFO rate after each injection. Increased UFO rate after MKI Flashover. • Next steps: UFO MD, MD Improve the diagnostics, better understanding of quench limits, learn from simulations. June, 14 th 2011 LHC Beam Operation Committee 24
Thank you for your Attention Further information: • T. Baer, “UFOs in the LHC”, Joint DESY and University of Hamburg Accelerator Physics Seminar, May 2011. Tobias Baer CERN BE/OP Tobias. Baer@cern. ch Office: +41 22 76 75379 June, 14 th 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. LHC Beam Operation Committee 25
Backup slides June, 14 th 2011 LHC Beam Operation Committee 26
UFOs in 2010 • 18 beam dumps due to UFOs. • 113 UFOs below threshold found in logging database. (E. Nebot) (03. 08. 2010 - 28. 10. 2010) J. Wenninger (since 07. 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) June, 14 th 2011 LHC Beam Operation Committee 27
Event Rate • 113 events below threshold found in 2010. (E. Nebot) • UFO rate: rate proportional to beam intensity. courtesy of E. Nebot June, 14 th 2011 LHC Beam Operation Committee 28
Calibration of Tloss courtesy of E. Nebot June, 14 th 2011 Correlation of Tloss and width of Gaussian fitted to post mortem turn-by-turn data. LHC Beam Operation Committee 29
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. June, 14 th 2011 LHC Beam Operation Committee 30
UFO Algorithm 1. Losses (RS 4) of at least two BLMs within 40 m are above 1 E-4 Gy/s. 2. A BLM is not taken into account if It is at a TCT It is in IP 3, IP 6 or IP 7 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. June, 14 th 2011 LHC Beam Operation Committee 31
LHC UFO Buster LHC Console Manager -> Fixed Displays -> BLM -> UFO Buster June, 14 th 2011 LHC Beam Operation Committee 32
UFO Detection • For 2010: 113 UFOs below threshold found in logging database. Nebot) • 5000 UFOs below threshold found so far. Most events are much below threshold. 4905 candidate UFOs at 3. 5 Te. V. nominal arc threshold 7 Te. V • For 2011: Online UFO detection by UFO Buster. Detects UFOs in BLM concentrator data (1 Hz). (E. “threshold” = lowest threshold in standard arc cell. June, 14 th 2011 LHC Beam Operation Committee 33
Dump on 01. 05. 2011 Dump of BLMQI. 04 L 2. B 1 E 20_MQY on RS 3, 4 and 5 Dump of BLMQI. 04 L 2. B 1 E 20_MQY on 320µs, 640µs and LHC Beam Operation Committee June, 14 th 2011 34
Dump on 01. 05. 2011 • From fit to losses (BLMEI. 05 L 2. B 1 E 10_MKI. D 5 L 2. B 1): Amplitude: 0. 63 Gy/s Width: 0. 29 ms June, 14 th 2011 LHC Beam Operation Committee 35
Correlation with Vacuum June, 14 th 2011 LHC Beam Operation Committee 36
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 of F. Zimmermann June, 14 th 2011 LHC Beam Operation Committee 37
Correlation with Wire Scanner courtesy of M. Sapinski (cf. Chamonix 2011) From wire scans: linear dependency of BLM signal on beam energy June, 14 th 2011 LHC Beam Operation Committee 38
Layout of MKI Region June, 14 th 2011 LHC Beam Operation Committee 39
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. courtesy of • From FLUKA simulations: size ≈ 1 μm. J. Wenninger (cf. MPP 25. 03. 2011) (cf. M. Sapinski, F. Zimmermann at Chamonix 2011) June, 14 th 2011 LHC Beam Operation Committee 40
UFO Speed • UFO speed: vu: UFO speed, σb: transverse beam size, σu: UFO size, σT: temporal width of loss. • From free fall: 22 mm free fall εnorm = 2. 5 µm·rad β = 150 m The UFO speed corresponds to the expected speed for a free fall from the aperture. June, 14 th 2011 LHC Beam Operation Committee 41
Known Dust Particle Sources • Distributed ion pumps (PF-AR, HERA). • Electrical Discharges (PF-AR). • Movable Devices. • Particles frozen or condensated at cold elements. (ANKA) June, 14 th 2011 LHC Beam Operation Committee 42
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