UFOs in the LHC Evian Workshop 2011 Tobias

UFOs in the LHC Evian Workshop 2011 Tobias Baer December, 13 th 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, … December 13 th 2011 Evian Workshop 2011 1

Content 1. Introduction, Observations and Correlations 2. MKI UFO Studies 3. Extrapolation for 2012 and beyond 4. Outlook and Summary December 13 th 2011 Evian Workshop 2011 2

Content 1. Introduction, Observations and Correlations 2. MKI UFO Studies 3. Extrapolation for 2012 and beyond 4. Outlook and Summary December 13 th 2011 Evian Workshop 2011 3

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 Ge. V. • Typical characteristics: • Loss duration: about 10 turns • Often unconventional loss locations (e. g. in the arc) • The events are believed to be due to (Unidentified) Falling Objects (UFOs). December 13 th 2011 Spatial and temporal loss profile of UFO on 23. 08. 2010 Evian Workshop 2011 4

Below Threshold UFOs 4513 arc UFOs (≥cell 12) at 3. 5 Te. V with signal RS 01 > 1∙ 10 -3 Gy/s. courtesy of J. M. Jimenez December 13 th 2011 Evian Workshop 2011 5

Spatial UFO Distribution • UFOs occur all around the machine. • Many UFOs around MKIs. Pt. 2 Pt. 3 Pt. 4 Pt. 5 Pt. 6 Pt. 7 Pt. 8 MKI • Some locations (especially right of Pt. 3) with increased number of UFOs: 25 R 3 B 2: 144 UFOs 19 R 3 B 1: 126 UFOs. 28 R 7 B 2: 118 UFOs. From MC: Probability to observe for one beam in one cell at least 40 events < 10 -6. (3164 events in B 2, 360 arc cells) December 13 th 2011 Evian Workshop 2011 7784 candidate UFOs at 3. 5 Te. V. Signal RS 04 > 2∙ 10 -4 Gy/s. Red: Signal RS 01 > 1∙ 10 -2 Gy/s. Gray areas around IRs are excluded from UFO detection 6

UFO rate 2011 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 RS 04 > 2∙ 10 -4 Gy/s. 1380 bunches TS #4 (29. 08 – 02. 09. 2011) 25 ns, 60 b Decrease of UFO rate from ≈10 UFOs/hour to ≈2 UFOs/hour. December 13 th 2011 Evian Workshop 2011 7

Content 1. Introduction, Observations and Correlations 2. MKI UFO Studies 3. Extrapolation for 2012 and beyond 4. Outlook and Summary December 13 th 2011 Evian Workshop 2011 8

Layout of MKI Region December 13 th 2011 Evian Workshop 2011 9

MKI UFOs • 11 dumps due to MKI UFOs in 2011. 10 dumps at MKI. D 5 L 2. 8 dumps at 3. 5 Te. V. 2 dumps during stable beams. 1236 UFOs around MKIs for fills lasting at least 3 hours after last injection. • In total 2340 UFOs around MKIs 847 in Pt. 2 and 1493 in Pt. 8. • Most events within 30 min after the last injection. Many events within a few hundred ms after MKI pulse. • First event 3 ms after MKI pulse. Compared to 62 ms for free fall from aperture. Could be explained by negatively charged particles. (F. Zimmermann at LIBD, 29 th Nov. 2011) December 13 th 2011 Evian Workshop 2011 10

FLUKA Simulations • UFO location must be in MKIs (or nearby upstream of MKIs). • At 3. 5 Te. V: 4· 1011 inelastic nuclear interactions per Gy at BLM after MKI. D 5 L 2. • Minimum particle radius of 40µm needed to explain UFO event on 16. 07. 2011 14: 09: 18. (T. Baer at LIBD, 29 th Nov. 2011) December 13 th 2011 A. Lechner and the FLUKA team Evian Workshop 2011 11

Macroparticles in MKIs • MKI#5 (removed from LHC in winter TS 2010/11) was opened and inspected for macroparticles including energy-dispersive X-ray spectroscopy. 100µm • Reference measurements: clean room air: 100 particles on filter new ceramic tube: 10‘ 000 particles on filter 10µm • 5‘ 000 particles on filter found in MKI#5 inspection. • Typical macroparticle diameter: 1 -100µm. • Most particles are Al 2 O 3 (material of ceramic tube). December 13 th 2011 courtesy of A. Gerardin, N. Garrel EDMS: 1162034 Evian Workshop 2011 Al O 12

UFO Model • Implemented in dust particle dynamics model, which predicts (among others): Loss duration of. Detaching a few ms. stimulated by vibration, electrical field Losses become faster for larger during MKI pulse and/or electrical beam potential. beam intensities. Al 2 O 3 fragment of vacuum chamber. Size: 1 -100µm. Interaction with beam Potentially charged leads to positive charging by electron cloud of UFO. Particle could be repelled by beam courtesy of F. Zimmermann, N. Fuster IPAC’ 11: MOPS 017 Beam loss rate as a function of time for different macroparticle masses. Beam intensity: 1. 6· 1014 protons. December 13 th 2011 Evian Workshop 2011 ceramic tube e- e- e 19 mm Metal strips for image currents Beam losses from inelastic nuclear interaction. 13

Content 1. Introduction, Observations and Correlations 2. MKI UFO Studies 3. Extrapolation for 2012 and beyond 4. Outlook and Summary December 13 th 2011 Evian Workshop 2011 14

25 ns Operation • Heavy UFO activity during 25 ns MDs (450 Ge. V). In 9. 1/13. 3 (B 1/B 2) hours with at least 1· 1013 protons per beam: 159 MKI UFOs. 22 arc UFOs. normal rate < 0. 5 UFOs/hour. TUPC 136) (E. Nebot, IPAC‘ 11, • UFO cascade observed in 30 L 3 B 2 (450 Ge. V) 12 UFOs at same location within 20 seconds. December 13 th 2011 Evian Workshop 2011 15

Energy Dependency • UFO amplitude: At 7 Te. V about 3 times higher than at 3. 5 Te. V (from wire scans). Complementary FLUKA results will be available for Chamonix. BLM 1 • BLM thresholds: Arc thresholds at 7 Te. V are about a factor 5 smaller than at 3. 5 Te. V. • UFO rate: No energy dependency would be consistent with observations. December 13 th 2011 Evian Workshop 2011 BLM 2 BLM 3 Wire scan during ramp courtesy of E. Nebot IPAC’ 11: TUPC 136 16

Energy Extrapolation From 2011 data: 81 UFO beam dumps by arc UFOs (≥ cell 12) for 7 Te. V, 3 dumps for 4 Te. V. (compared to 2 dumps at 3. 5 Te. V). Expected number of UFO related beam dumps from events between 14. 04. and 31. 10. 2011. Expected scaling of BLM signal/threshold with energy. • Assumes identical running conditions as 2011. Not included: margin between BLM thresholds and actual quench limit, 25 ns bunch spacing, intensity increase, beam size, scrubbing, MKI UFOs. December 13 th 2011 Evian Workshop 2011 17

Content 1. Introduction, Observations and Correlations 2. MKI UFO Studies 3. Extrapolation for 2012 and beyond 4. Outlook and Summary December 13 th 2011 Evian Workshop 2011 18

Plans and Suggestions for 2012 • Better localization of arc UFOs by installation of additional mobile monitors in one arc cell. 80µs time resolution in study buffer. • FLUKA simulations for arc UFOs. Underway, first results expected for Chamonix. • Better understanding of quench limit: limit Increase BLM thresholds for UFO type losses to probe quench limit. Wire scanner quench test. • Study impact on 25 ns operation. 25 ns high intensity (> 1000 bunches) beam for several hours at flat top. • MKI UFO MD. Study MKI asymmetry, particle dynamics, 25 ns, e-cloud correlation. • Develop mitigation strategy for MKIs. E. g. different cleaning of ceramic tubes, new design of inner structure. December 13 th 2011 Evian Workshop 2011 19

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 detected • In 2011 large effort to understand UFOs, especially at MKIs. Event rate for arc UFOs decreased by a factor 5 throughout 2011. Improved diagnostics, MDs, lab measurements, FLUKA simulations, theoretical studies. • For 2012: No sign that the situation should become much worse. • After LS 1: Aggressive scaling with energy observed/expected. Studies in 2012 needed for better understanding, extrapolation and mitigation. December 13 th 2011 Evian Workshop 2011 20

Thank you for your Attention Further information: • T. Baer et al. , “UFOs in the LHC”, IPAC’ 11, TUPC 137. • E. Nebot et al. , “Analysis of Fast Losses in the LHC with the BLM System”, IPAC’ 11, TUPC 136. Tobias Baer CERN BE/OP Tobias. Baer@cern. ch Office: +41 22 76 75379 December 13 th 2011 • N. Fuster et al. , “Simulation Studies of Macroparticles Falling into the LHC Proton Beam”, IPAC’ 11, MOPS 017. • 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. Evian Workshop 2011 21

Backup slides December 13 th 2011 Evian Workshop 2011 22

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. December 13 th 2011 Evian Workshop 2011 23

UFO rate vs Bunch Intensity No dependency of UFO rate on buch intensity. December 13 th 2011 Evian Workshop 2011 24

Peak Signal vs Loss Duration courtesy of E. Nebot December 13 th 2011 Tendency that harder UFOs are faster. Evian Workshop 2011 25

Intrafill UFO rate The UFO rate stays constant during a fill. December 13 th 2011 Evian Workshop 2011 26

Number of MKI UFOs 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 On average: 8. 9 MKI UFOs per fill (3. 4 at MKI. L 2 and 5. 5 at MKI. R 8). December 13 th 2011 Evian Workshop 2011 27

Number of MKI UFOs 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 During the UFO storms in July 2011 there was an increased number of UFOs with large signal. The cause is still not understood. December 13 th 2011 Evian Workshop 2011 28

Vacuum Valve Movement VVGST. 101. 5 L 2. B VVGST. 101. 5 L 2. R VVGST. 136. 5 L 2. B VVGST. 136. 5 L 2. R VVGST. 140. 5 L 2. R VVGST. 175. 5 L 2. B VVGST. 175. 5 L 2. R VVGST. 101. 5 L 2. B VVGST. 101. 5 L 2. R VVGST. 140. 5 L 2. B VVGST. 140. 5 L 2. R VVGST. 175. 5 L 2. B VVGST. 175. 5 L 2. R VVGST. 193. 5 L 2. B VVGST. 21. 5 L 2. R VVGST. 3. 5 L 2. B VVGST. 56. 5 L 2. R VVGST. 61. 5 L 2. B VVGST. 61. 5 L 2. R VVGST. 96. 5 L 2. B VVGST. 96. 5 L 2. R MKI Beam 1 152 candidate UFOs around injection regions in Pt. 2 for fills reaching stable beams. Signal RS 01 > 1∙ 10 -2 Gy/s. VVGST. 101. 5 L 2. B VVGST. 101. 5 L 2. R VVGST. 136. 5 L 2. B VVGST. 136. 5 L 2. R VVGST. 140. 5 L 2. B VVGST. 140. 5 L 2. R VVGST. 175. 5 L 2. B VVGST. 175. 5 L 2. R VVGST. 193. 5 L 2. B VVGST. 21. 5 L 2. R VVGST. 3. 5 L 2. B VVGST. 56. 5 L 2. R VVGST. 61. 5 L 2. B VVGST. 61. 5 L 2. R VVGST. 96. 5 L 2. B VVGST. 96. 5 L 2. R No correlation with closure of vacuum valves. orange: orange Several valves closed, blue: blue VVGST. 193. 5 L 2 and VVGST. 3. 5 L 2 closed, green: green status unknown for several valves. December 13 th 2011 Evian Workshop 2011 29

Macro Particle Size t s u m s O F U e g r a l f o. s m u µ i 0 d 4 a R Particle mass t least ≈ UFO event on 16. 07. 2011 14: 09: 18 be a I=1. 02· 1014 protons, E=3. 5 Te. V, with ԑn=2. 5µm·rad, βx=158. 5 m, βy=29. 5 m, σx=325µm, σy=140µm. Nuclear interaction length Material Resulting mass (A) Radius of spherical object Al (l=39. 7 cm, ρ=2700 kg/m 3) 5. 53· 1017 43µm Al 2 O 3 (l=24. 8 cm, ρ=3970 kg/m 3) 5. 08· 1017 37µm December 13 th 2011 Evian Workshop 2011 30

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). nm courtesy of R. Moron Ballester, S. Redaelli EDMS: 1153686 December 13 th 2011 Evian Workshop 2011 31

Lead MKI UFOs IP 8 MQML. 10 L 8 (highest loss) MKI UFO at MKI. D 5 R 8. TCTH MKI (UFO location) 10 % of threshold at MQML. 10 L 8. Losses are not as localized as for protons. Highest loss is in the dispersion suppressor downstream of the IR (due to ion fragmentation). Horizontal dispersion December 13 th 2011 Evian Workshop 2011 32