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UFOs in the LHC

UFOs in the LHC. Evian Workshop 2011 Tobias Baer December, 13 th 2011.

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UFOs in the LHC

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  1. UFOs in the LHC • Evian Workshop 2011 Tobias Baer December, 13th 2011 Acknowledgements: G. Arduini, W. Bartmann, M. Barnes, C. Bracco, F. Cerutti, B. Dehning, L. Ducimetiere, A. Ferrari, M. Ferro-Luzzi, N. Fuster Martinez, N. Garrel, A. Gerardin, B. Goddard, E.B. Holzer, S. Jackson, M. Jimenez, V. Kain, A. Lechner, V. Mertens, M. Misiowiec, R. Moron Ballester, E. Nebot, L. Norderhaug Drosdal, A. Nordt, S. Redaelli, J. Uythoven, B. Velghe, V. Vlachoudis, J. Wenninger, C. Zamantzas, F. Zimmermann, …

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  4. UFOs in the LHC • Since July 2010, 35 fast loss events led to a beam dump.18 in 2010, 17 in 2011.Over the two years: 13 around MKIs. 6 dumps by experiments. 1 at 450 GeV. • Typical characteristics: • Loss duration: about 10 turns • Oftenunconventionallosslocations (e.g. in thearc) • The events are believed to be due to (Unidentified) Falling Objects (UFOs). Spatialand temporal lossprofileof UFO on 23.08.2010

  5. Below Threshold UFOs • In 2011: 16,000 candidate UFOs below dump threshold found. • Measured distribution of BLM signal is consistent with measured dust distribution in SM12/Bat113.Linear dependency of UFO signal on particle volume shown by N. Fuster et al., IPAC’11, MOPS017. 4513 arc UFOs (≥cell 12) at 3.5 TeVwith signal RS01 > 1∙10-3Gy/s. courtesy of J. M. Jimenez

  6. Spatial UFO Distribution • UFOs occur all around the machine. • Many UFOs around MKIs. • Some locations (especially right of Pt. 3) with increased number of UFOs:25R3 B2: 144 UFOs 19R3 B1: 126 UFOs. 28R7 B2: 118 UFOs. From MC: Probability to observe for one beam in one cell at least 40 events < 10-6. (3164 events in B2, 360 arc cells) Pt.2 Pt.3 Pt.4 Pt.5 Pt.6 Pt.7 Pt.8 MKI MKI 7784 candidate UFOs at 3.5 TeV. Signal RS04 > 2∙10-4Gy/s. Red: Signal RS01 > 1∙10-2Gy/s. Gray areas around IRs are excluded from UFO detection

  7. UFO rate 2011 • Decreaseof UFO rate from ≈10 UFOs/hourto ≈2 UFOs/hour. TS #2 (09. – 13.05.2011) TS #3 (04. – 08.07.2011) 5242 candidate arc UFOs (≥ cell 12) during stable beams between 14.04. and 31.10.2011. Fills with at least 1 hour stable beams are considered. Signal RS04 > 2∙10-4Gy/s. 1380 bunches TS #4 (29.08 – 02.09.2011) 25ns, 60b

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  9. Layout of MKI Region

  10. MKI UFOs • 11 dumps due to MKI UFOs in 2011.10 dumps at MKI.D5L2. 8 dumps at 3.5 TeV. 2 dumps during stable beams. • In total 2340 UFOs around MKIs 847 in Pt.2 and 1493 in Pt.8. • Most events within 30min after the last injection. Many events within a few hundred ms after MKI pulse. • First event 3ms after MKI pulse. Compared to 62ms for free fall from aperture. Could be explained by negatively charged particles.(F. Zimmermann at LIBD, 29th Nov. 2011) 1236 UFOs around MKIs for fills lasting at least 3 hours after last injection.

  11. FLUKA Simulations • UFO location must be in MKIs (ornearbyupstreamof MKIs). • At 3.5 TeV: 4·1011inelasticnuclearinteractionsper Gy atBLM after MKI.D5L2. • Minimum particleradiusof 40µm neededtoexplainUFO event on 16.07.2011 14:09:18.(T.Baer at LIBD, 29th Nov. 2011) A. Lechner and the FLUKA team

  12. Macroparticlesin MKIs • MKI#5 (removedfromLHC in winter TS 2010/11) was openedandinspectedformacroparticlesincludingenergy-dispersiveX-rayspectroscopy. • Reference measurements:clean roomair: 100 particles on filternewceramictube: 10‘000 particles on filter • 5‘000‘000 particles on filterfound in MKI#5 inspection. • Typicalmacroparticlediameter: 1-100µm. • Most particlesareAl2O3 (material ofceramictube). 100µm 10µm Al O courtesy of A. Gerardin, N. Garrel • EDMS: 1162034

  13. UFO Model Al2O3 fragment of vacuum chamber. Size: 1-100µm. • Implemented in dustparticledynamicsmodel, whichpredicts (amongothers): • Loss duration of a few ms. • Losses become faster for larger beam intensities. Detaching stimulated by vibration, electrical field during MKI pulse and/or electrical beam potential. ceramictube e- Potentially charged by electron cloud e- Metal strips for image currents e- Interaction with beam leads to positive charging of UFO. Particle could be repelled by beam 19mm Beam courtesy of F. Zimmermann, N. FusterIPAC’11: MOPS017 Beam losses from inelastic nuclear interaction. Beam loss rate as a functionof time for different macroparticlemasses. Beam intensity: 1.6·1014protons.

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  15. 25ns Operation • Heavy UFO activityduring 25ns MDs (450 GeV). In 9.1/13.3 (B1/B2) hourswithat least 1·1013protons per beam:159 MKI UFOs.22 arc UFOs. normal rate < 0.5 UFOs/hour. (E. Nebot, IPAC‘11, TUPC136) • UFO cascadeobserved in 30L3 B2 (450 GeV) 12 UFOs at same locationwithin 20 seconds.

  16. Energy Dependency • UFO amplitude:At7TeV about3 timeshigherthanat3.5TeV (fromwirescans).Complementary FLUKA results will be available for Chamonix. • BLM thresholds: Arc thresholds at 7TeV are about a factor 5 smaller than at 3.5TeV. • UFO rate: Noenergydependencywouldbeconsistentwithobservations. BLM 1 Wirescanduringramp BLM 2 BLM 3 courtesy of E. NebotIPAC’11: TUPC136

  17. Energy Extrapolation • From 2011 data: 81 UFO beam dumpsbyarc UFOs(≥ cell 12) for 7TeV, 3 dumpsfor 4TeV.(comparedto 2 dumpsat3.5TeV). • Assumesidenticalrunningconditionsas 2011. Not included: marginbetween BLM thresholdsandactualquenchlimit,25ns bunchspacing,intensityincrease,beam size, scrubbing, MKI UFOs. Expectednumberof UFO related beam dumpsfromeventsbetween 14.04. and 31.10.2011. Expectedscalingof BLM signal/thresholdwithenergy.

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  19. Plans andSuggestionsfor 2012 • Betterlocalizationofarc UFOs byinstallationof additional mobile monitors in onearccell. 80µs time resolution in studybuffer. • FLUKA simulationsforarc UFOs.Underway, firstresultsexpectedfor Chamonix. • Betterunderstandingofquenchlimit:Increase BLM thresholdsfor UFO type lossesto probe quenchlimit.Wirescannerquenchtest. • Study impact on 25ns operation.25ns high intensity(> 1000 bunches) beam forseveralhoursat flat top. • MKI UFO MD.Study MKI asymmetry, particledynamics, 25ns, e-cloudcorrelation. • Developmitigationstrategyfor MKIs.E.g. different cleaningofceramictubes, new design ofinnerstructure.

  20. Summary • 17 beam dumps due to UFOs in 2011 (18 in 2010).Due to large-scale increases/optimization of the BLM thresholds and UFO scrubbing, the impact of UFOs could be mitigated in the second half of 2011. • 16’000 candidate UFOs below threshold detectedEvent rate for arc UFOs decreased by a factor 5 throughout 2011. • In 2011 large effort to understand UFOs, especially at MKIs.Improved diagnostics, MDs, lab measurements, FLUKA simulations, theoretical studies. • For 2012: No sign that the situation should become much worse. • After LS1: Aggressive scaling with energy observed/expected. Studies in 2012 needed for better understanding, extrapolation and mitigation.

  21. Thank you • for your Attention • Tobias Baer • CERN BE/OP • Tobias.Baer@cern.ch • Office: +41 22 76 75379 • Further information: • T. Baer et al., “UFOs in the LHC”, IPAC’11, TUPC137. • E. Nebot et al., “Analysis of Fast Losses in the LHC with the BLM System”, IPAC’11, TUPC136. • N. Fuster et al., “Simulation Studies of Macroparticles Falling into the LHC Proton Beam”, IPAC’11, MOPS017. • R. Ballester, “Vibration Analysis on an LHC Kicker Prototype for UFOs Investigation”, EDMS Report No. 1153686. • A. Gerardin et al., “EDS Analyses of Filters used for UFO Sampling”, EDMS Report No: 1162034.

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  23. 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.

  24. UFO rate vsBunchIntensity • Nodependencyof UFO rate on buch intensity.

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

  26. Intrafill UFO rate • The UFO rate stays constant during a fill. 3185 arc UFOs (cell 12) between 14.04. and 31.10.2011 during stable beams in 47 fills with at least 10 hours stable beams. Signal RS04 > 2∙10-4Gy/s.

  27. Number of MKI UFOs • On average: 8.9 MKI UFOs per fill(3.4 at MKI.L2 and 5.5 at MKI.R8). MKI UFO storms in Pt. 2 1664 UFOs around injection kicker magnets between 14.04. and 31.10.2011 in Pt. 2 and Pt.8 for fills reaching stable beams with >100 bunches. After MKI flashover

  28. Number of MKI UFOs • Duringthe UFO storms in July 2011 there was an increasednumberof UFOs with large signal. The causeis still not understood. MKI UFO storms in Pt. 2 1664 UFOs around injection kicker magnets between 14.04. and 31.10.2011 in Pt. 2 and Pt.8 for fills reaching stable beams with >100 bunches. After MKI flashover

  29. Vacuum Valve Movement • No correlation with closure of vacuum valves. orange: Several valves closed, blue: VVGST.193.5L2 and VVGST.3.5L2 closed, green: status unknown for several valves. VVGST.101.5L2.B VVGST.101.5L2.R VVGST.136.5L2.B VVGST.136.5L2.R VVGST.140.5L2.B VVGST.140.5L2.R VVGST.175.5L2.B VVGST.175.5L2.R VVGST.193.5L2.B VVGST.21.5L2.B VVGST.21.5L2.R VVGST.3.5L2.B VVGST.56.5L2.B VVGST.56.5L2.R VVGST.61.5L2.B VVGST.61.5L2.R VVGST.96.5L2.B VVGST.96.5L2.R VVGST.101.5L2.B VVGST.101.5L2.R VVGST.136.5L2.B VVGST.136.5L2.R VVGST.140.5L2.B VVGST.140.5L2.R VVGST.175.5L2.B VVGST.175.5L2.R VVGST.193.5L2.B VVGST.21.5L2.B VVGST.21.5L2.R VVGST.3.5L2.B VVGST.56.5L2.B VVGST.56.5L2.R VVGST.61.5L2.B VVGST.61.5L2.R VVGST.96.5L2.B VVGST.96.5L2.R MKI Beam 1 152 candidate UFOs around injection regions in Pt. 2 for fills reaching stable beams. Signal RS01 > 1∙10-2Gy/s. VVGST.101.5L2.B VVGST.101.5L2.R VVGST.140.5L2.B VVGST.140.5L2.R VVGST.175.5L2.B VVGST.175.5L2.R VVGST.193.5L2.B VVGST.21.5L2.B VVGST.21.5L2.R VVGST.3.5L2.B VVGST.56.5L2.B VVGST.56.5L2.R VVGST.61.5L2.B VVGST.61.5L2.R VVGST.96.5L2.B VVGST.96.5L2.R VVGST.101.5L2.B VVGST.101.5L2.R VVGST.136.5L2.B VVGST.136.5L2.R VVGST.140.5L2.R VVGST.175.5L2.B VVGST.175.5L2.R

  30. MacroParticle Size • From FLUKA simulations:4.07·1011interactions per Gy atBLMEI.05L2.B1E10_MKI.D5L2.B1 at 3.5 TeV. • Peak lossof 8.45 Gy/s correspondsto 3.44·1012interactions/s. • With (r << σ) Radius of large UFOs must beat least ≈40µm. UFO event on 16.07.2011 14:09:18 Particlemass I=1.02·1014protons, E=3.5 TeV, with ԑn=2.5µm·rad, βx=158.5m, βy=29.5m, σx=325µm, σy=140µm. Nuclearinteractionlength

  31. Vibration Measurements • Measurements carried out on spare MKI with kicker pulsing at full voltage under vacuum using accelerometers and laser vibrometers. • Many issues of electrical noise and spurious vibration (e.g. pumps) • When the kickers fire, a mechanical vibration in 60-300 Hz range is measured. The amplitudes are but very small (≈10 nm). courtesy of R. Moron Ballester, S. RedaelliEDMS: 1153686

  32. Lead MKI UFOs • MKI UFO at MKI.D5R8. • 10 % of threshold at MQML.10L8.Losses are not as localized as for protons. • Highest loss is in the dispersion suppressor downstream of the IR (due to ion fragmentation). IP8 MQML.10L8 (highestloss) MKI (UFO location) TCTH Horizontal dispersion

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