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LIBD MeetingNovember 29th 2011 1
MKI UFOs
LIBD MeetingTobias BaerNovember, 29th 2011
Acknowledgements: M. Barnes, C. Bracco, N. Garrel, B. Goddard, S. Jackson, V. Mertens, M. Misiowiec, E. Nebot, A. Nordt, J. Uythoven, J. Wenninger, C. Zamantzas, F. Zimmermann, …
LIBD MeetingNovember 29th 2011 2
Content
1. Lead MKI UFOs
2. Update on MKI UFO MD results
3. UFO size estimates
4. IPAC Abstract
LIBD MeetingNovember 29th 2011 3
Content
1. Lead MKI UFOs
2. Update on MKI UFO MD results
3. UFO size estimates
4. IPAC Abstract
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Lead MKI UFOs
MKI UFO at MKI.D5R8.10 % of threshold at MQML.10L8.Losses are not localized as for protons.
Highest loss is in the dispersion suppressor downstream of the IR (due to ion fragmentation).
Horizontal dispersion
MKI (UFO location)
MQML.10L8 (highest loss)
IP8
TCTH
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Content
1. Lead MKI UFOs
2. Update on MKI UFO MD results
3. UFO size estimates
4. IPAC Abstract
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Delay of UFO events
In total 57 UFO events44 at MKIs in Pt.8 (41 pulses)13 at MKIs in Pt.2 (35 pulses)
The distribution looks similar for the MKIs in Pt. 2 and Pt. 8.
The first clear events occured 10.2ms after pulsing the MKIs.UFO detection in first ≈20ms is limited by transient losses during MKI pulse.
zoomed
1 event at 1330 ms
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Delay of UFO events
The distribution spreads out over a few hundred ms. The first event was observed about 3ms after MKI pulse (in IQC).
1 event at 1330 ms
zoomedUFOs in IQCuntil 11.08.2011
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UFO Location
In Pt. 2 most UFOs occur at MKI.D5L2. In Pt. 8 the distribution is more equal.
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Content
1. Lead MKI UFOs
2. Update on MKI UFO MD results
3. UFO size estimates
4. IPAC Abstract
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Macro Particle Size
F. Zimmermann at LMC 109
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Macro Particle Size
• From FLUKA simulations:4.07·1011 interactions per Gy atBLMEI.05L2.B1E10_MKI.D5L2.B1at 3.5 TeV.
• Peak loss of 8.45 Gy/s corresponds to 3.44·1012 interactions/s.
• With (r << σ) UFO event on 16.07.2011 14:09:18I=1.02·1014 protons, E=3.5 TeV, with ԑn=2.5µm·rad, βx=158.5m, βy=29.5m, σx=325µm, σy=140µm.
Material Resulting mass (A) Radius of spherical object
Al (l=39.7cm, ρ=2700kg/m3) 5.53·1017 43µm
Al2O3 (l=24.8cm, ρ=3970kg/m3) 5.08·1017 37µm
Particle mass
Nuclear interaction length
Radius of large UFOs must
be at least ≈40µm.
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Content
1. Lead MKI UFOs
2. Update on MKI UFO MD results
3. UFO size estimates
4. IPAC Abstract
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IPAC Abstract
UFOs in the LHCT. Baer, M. Barnes, N. Fuster Martinez (U. Valencia), N. Garrel, B. Goddard,E.B. Holzer, A. Lechner, V. Mertens, E. Nebot del Busto, A. Nordt, J. Uythoven,J. Wenninger, F. Zimmermann, …
One of the major known limitations for nominal operation of the Large Hadron Collider is so called UFOs (Unidentified Falling Objects). UFOs are thought to be micrometer to millimeter sized dust particles which lead to fast beam losses, with a duration of the order of 10 turns, when they interact with the beam. The first UFO events were observed in July 2010 and they have caused 35 protection beam dumps since then. In 2011, the diagnostics for such events were significantly improved, dedicated experiments and measurements in the LHC and in the laboratory were made and complemented by simulations and theoretical studies. This allows estimates of the properties, dynamics and production mechanisms of the dust particles. The state of knowledge, extrapolations to nominal LHC parameters and mitigation strategies are presented.
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Thank you for your Attention
Tobias BaerCERN BE/[email protected]: +41 22 76 75379
Further information:• T. Baer, “UFO update”, Mini-Chamonix Workshop, July 2011.
• R. Ballester, “Vibration analysis on an LHC kicker prototype for UFOs investigation”, EDMS Report No. 1153686, August 2011.
• M. Sapinski, “Is the BLM system ready to go to higher intensities?”, Workshop on LHC Performance, Chamonix, Jan. 2011.
• F. Zimmermann, “Interaction of macro-particles with the LHC proton beam”, IPAC’10.
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Backup slides
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Study buffer provides information about temporal and spatial distribution as well as amplitude of UFOs after MKI pulse.
UFO at 09:54:28
11.2s2.56ms resolution
Losses of unbuched
beam at TDI
UFOs
beam
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Temporal Loss pattern
Temporal loss pattern of the MKI UFO at 24.11.2011 13:58:38 at three different BLMs left and right of IP8.
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Content
UFO Dumps 2010/2011
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UFOs in the LHC
• Since July 2010, 35 fast loss events led to a beam dump.
18 in 2010, 17 in 2011.13 around MKIs.6 dumps by experiments.1 at 450 GeV.
• 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). Spatial and temporal loss profile of UFO on 23.08.2010
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Beam dump on 29.05.2011
Dump on running sum 1-6.
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Beam dump 29.05.2011
• From fit to losses (BLMQI.28L8.B1E10_MQ):
• Amplitude: 2.4 Gy/s(Threshold: 2.1 Gy/s)
• Temporal Width: 97 µsresulting speed of transiting dust particle = 3.6 m/s.(assuming ϵn=2.5µm·rad)
(also cf. J. Wenninger at MPP March 2011)
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Content
UFO Observations and Studies
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• 2010: Logged BLM data was analyzed and 113 sub-threshold UFO events were found. (E. Nebot)
• For 2011: Online UFO detection in 1Hz BLM data.
• Over 10000 candidate UFOsbelow threshold found.
Most events are muchbelow threshold.
• Between 2010 and 2011,UFO related beam dumpswere reduced by increasingthe BLM thresholds for losseson ms scale by a factor 5.
UFOs Below Dump Threshold
∝𝐱−𝟏 .𝟎𝟎
Distribution of arc UFOs.
2780 arc UFOs (≥cell 12) at 3.5 TeV with signal RS05 > 2∙10-4 Gy/s.
∝ 𝒙−𝟏 .𝟎𝟎
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Spatial UFO Distribution
3.5 TeV3686 candidate UFOs.
Signal RS05 > 2∙10-4 Gy/s.Red: Signal RS01 > 1∙10-2 Gy/s.
UFOs occur all around the machine.
Many UFOs around injection kicker magnets (MKIs).
450 GeV486 candidate UFOs.
Signal RS05 > 2∙10-4 Gy/s.
Mainly UFOs around MKIs
gray areas around IRs are excluded from UFO detection.
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On average 6.0 UFOs/hour.No intensity dependency for above a few hundred bunches.
UFO rate
5238 candidate UFOs in cell 12 or larger during stable beams. Fills with at
least 1 hour stable beams are considered.
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Intrafill UFO rate
The UFO rate stays constant during a fill.
3375 candidate arc UFOs (cell 12) during stable beams in 31 fills with at least 10 hours stable beams.
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• Ufo amplitude: At 7 TeV about 3 times higher than at 3.5TeV. (from wire scans). (E. Nebot, IPAC 2011)
• BLM thresholds: Arc thresholds at7 TeV are about a factor 5 smallerthan at 3.5 TeV.
• UFO rate: No energy dependency would be competative with observations. (E. Nebot, IPAC 2011)
• From 2011 data: 82 UFO beam dumps by arc UFOs for 7 TeV(compared to 2 actual dumps at 3.5 TeV).
Energy Dependency
Wire scan during ramp
E. N
ebot
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The measured distribution of dust particles in SM12/Bat113 would explain the UFO distribution.
UFOs and Dust Particle Distribution
3670 arc UFOs (>cell 12) at 3.5 TeV with signal RS01 > 1∙10-3 Gy/s.
∝ 𝒙−𝟎.𝟗𝟐 ∝ 𝒙−𝟎.𝟗𝟕
courtesy of J. M. Jimenez
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Dynamics of Dust Particles
From simulations:
• Dust particle will be positively ionized and be repelled from the beam.
• Loss duration of a few ms.
• Losses become faster for larger beam intensities.
courtesy of F. Zimmermann
4.6 10∙ 13 protons3.5 TeV
2.3 10∙ 12 protonsround Al Object
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Loss Duration
UFOs have the tendency to become faster with increasing intensity.
(cf. E.B. Holzer at Evian Dec. 2010)
courtesy ofE. Nebot
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Event Rate 2010
• 113 events below threshold found in 2010. (E. Nebot)
• UFO rate: proportional tobeam intensity.
courtesy ofE. Nebot
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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 10000 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∙ -4 Gy/s (≈ 2 ‰ of
threshold).74 events remain of subset, of which 71 are clear UFOs (96%) and 3 are
ambiguous cases.
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Weighted Spatial UFO Distribution
The weighted spatial distribution isdominated by a few large amplitude UFOs.
28L8around
WS/BSRT
MKIs 5875 candidate UFOs at 3.5 TeV. Gray areas around IRs are excluded from UFO
detection.
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Normalized UFO rate
2194 candidate UFOs during stable beams in fills with at least 1 hour stable beams.Signal RS05 > 2∙10-4 Gy/s. Data scaled with 1.76 (detection efficiency from reference data)
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Peak Signal
• 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.
courtesy ofE. Nebot
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UFO rate vs Bunch Intensity
No dependency of UFO rate on buch intensity.
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Peak Signal vs Loss Duration
Tendency that harder UFOs are faster.courtesy of
E. Nebot
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Loss Duration
Tloss: Given by fitting single function (Gaussian up to t=Tloss, 1/t afterwards) to data.
• )
courtesy ofE. Nebot
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Calibration of Tloss
Correlation of Tloss and width of Gaussian fitted topost mortem turn-by-turn data.courtesy of
E. Nebot
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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)
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UFO Speed
• UFO speed:
• From free fall:
The UFO speed corresponds to the expected speed for a free fall from the aperture.
T
b
T
UbUv
22
vu: UFO speed, σb: transverse beam size, σu: UFO size,
σT: temporal width of loss.
22 m
m f
ree
fall
εnorm = 2.5 µm·radβ = 150 m
sm
U hgv 63.02
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Content
UFOs around MKIs
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• 13 beam dumps due to UFOs around the injection kicker magnets (MKIs)
10 dumps at MKI.D5L2
• In total ≈1500 UFOs around MKIs 614 in Pt.2 and 874 in Pt.8
Most events within 30minafter the last injection.
MKI UFOs
479 candidate UFOs around injection regions for fills lasting at least 3 hours after last injection.
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Layout of MKI Region
MKI.D MKI.C MKI.B MKI.A
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UFOs at MKIs
• In Pt.2 most MKI UFOs start at the BLM after MKI.D5L2.• In Pt.8 less UFOs start at the MKI.A5R8.
Left of IP2
Beam direction
174 candidate UFOs around MKI in Pt.2. Signal RS01 > 1∙10-3 Gy/s.
Right of IP8
Beam direction
270 candidate UFOs around MKI in Pt.8. Signal RS01 > 1∙10-3 Gy/s.
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MKI UFO MD
21 pulses of MKIs, 43 UFO type loss pattern observed.In 17 cases: UFO type loss pattern within the second of MKI pulse.
In 2 cases: UFO recorded by BLM injection capture buffer.
TDI 4R8
MKI D 5R8
UFOKicker pulse
beam
Spatial loss pattern Temporal loss pattern
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UFO Dynamics
• From fit to losses (MKI-D):
• Amplitude: 1.8·10-2 Gy/s(Threshold: 11.6 Gy/s)
• Temporal Width: 160 µs
• Time delay to kicker pulse: 7.6 ms• resulting acceleration (constant
particle acceleration): 658 m/s²• resulting speed during interaction
with beam: 5.0 m/s
• UFO type loss signal observed after many normal injections.
7.6ms
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Beam dump on 6.6.2011
UFO at MKI in Pt. 2, at 450 GeV.Small loss signal at Q5 (backscattering?).
MKIs
TCT
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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 msresulting speed of transiting dust particle = 0.47 m/s.(assuming ϵn=2.2µm·rad)
(Brennan Goddard)
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MKI UFOs During Scrubbing
• Typical scenario for MKI UFOs during scrubbing: The MKI UFO rate is increased for about 10 minutes after each injection.
2 hours
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Number of MKI UFOs
On average: 9.4 MKI UFOs per fill (5.4 at MKI.L2 and 3.9 at MKI.R8).
After MKI flashover
1042 candidate UFOs around injection regions in Pt. 2 and Pt.8 for fills reaching stable beams with >200 bunches.MKI UFO
storms in Pt. 2
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Number of Large MKI UFOs B1
The large number of strong MKI UFOs in Pt. 2 disappeared in the fills after the technical stop.
MKI Beam 1160 candidate UFOs around injection regions in Pt. 2 for fills reaching stable
beams with >200 bunches.Signal RS01 > 1∙10-2 Gy/s.
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MKI UFO Storms
• Fill 1898 (26th June): 15 UFOs MKI B1, 7 UFOs MKI B2.• 14 UFOs at MKI B1 within 40 min.• Highest UFO: 34% of Threshold at TCTH.4L2 (RS1, RS2) at 3.5 TeV.
• Fill 1900 (27th June): 32 UFOs MKI B1, 5 UFOs MKI B2.• 17 UFOs at MKI B1 within 6 min.• Highest UFO: 65% of Threshold at MQY.04L2 (RS6) at 3.5 TeV.
• Fill 1901 (28th June): 41 UFOs MKI B1, 12 UFOs MKI B2.• 16 UFOs at MKI B1 in 2:20 min.• Mostly at 450 GeV (12 min. at 450 GeV after last injection).• Highest UFO: 63% of Threshold at TCTH.4L2 (RS8) at 450 GeV.
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Number of large MKI UFOs B2
The number of large MKI UFOs in Pt. 8 did not increase.
MKI Beam 270 candidate UFOs around injection
regions in Pt. 8 for fills reaching stable beams. Signal RS01 > 1∙10-2 Gy/s.
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Vacuum Valve Movement
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.BVVGST.101.5L2.RVVGST.136.5L2.BVVGST.136.5L2.RVVGST.140.5L2.RVVGST.175.5L2.BVVGST.175.5L2.R
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.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 1152 candidate UFOs around injection regions in Pt. 2 for fills reaching stable
beams. Signal RS01 > 1∙10-2 Gy/s.
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UFO Location
• Sometimes BLMs upstream of the BLM with the highest have only slighly smaller losses.
• Analyzing first BLM above minsignal (as defined in plot)
BLMQI.05R8.B1I10_MQY
minsignal = 75% of difference in log scale.
UFO BLM
First BLM to see UFO
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UFOs at MKIs
• 08.04. – 05.05. in total 460 fast loss events around MKIs. (104 around MKI in IP2, 336 around MKI in IP8).
Distribution of first BLM which sees the loss:
Left of IP2 Right of IP8
Beam direction Beam direction
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Correlation with Vacuum
Despite a large vacuum spike, there is no clear correlation with UFOs
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Correlation with Vacuum
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Vacuum Correlation
The pressure spike is seen on all MKI magnets.
BLM MKI.C5L2
Vacuum MKI
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Dust Particles in the LHC
Samples from non-operational and old equipment. But not representative for the LHC…
1mm
Dust particles in Penning gauge from lab.
courtesy ofN. Garrel and
V. Mertens
Dust particles in ceramic test beam tube.
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Vacuum correlation (slow)
The slow vacuum spike is correlated to the last injection.No correlation with UFOs
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UFOs in IQC
Many additional events in IQC data for normal operation.
Loss at Injection Candidate UFO
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Content
MKI UFO MD
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MKI UFO MD
In 17 cases: UFO type loss pattern
21 pulses of MKIs, 43 UFO type loss pattern observed.In 17 cases: UFO type loss pattern within the second of MKI pulse.
Pulses MKI-APulses MKI-D
Losses at MKI-D (green) and MKI-A
(brown)
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UFOs between kicker pulses
The number of UFOs between kicker pulses decreased over time after the last injection with beam.
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MKI UFOs at MKI pulse
The peak loss at the MKI D in the second of the kicker pulse are 1.4 10∙ -2 Gy/s (40µs running sum).
TDI
MKI D
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The peak loss at the MKI D at injection is one order of magnitude smaller (1.4·10-3 Gy/s).
Losses at MKI
Loss at Kicker pulse
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UFO Dynamics
• From fit to losses (MKI-D):
• Amplitude: 3.7·10-3 Gy/s(Threshold: 11.6 Gy/s)
• Temporal Width: 218µsresulting speed of transiting dust particle
= 2.2 m/s.(assuming ϵn=2.5µm·rad)
• Time delay to kicker pulse: 4.3 msresulting acceleration (assuming constant particle acceleration):
2055 m/s²resulting speed during interaction with beam: 8.8 m/s
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Content
Conclusion and Summary
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Known Dust Particle Sources
• Distributed ion pumps (PF-AR, HERA).No ion pumps in LHC arcs.
• Electrical Discharges (PF-AR).
• Movable Devices (LHC).
• Particles frozen to or condensated at cold elements. (ANKA)
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Conclusion
• For 2011: • Arc UFOs: No sign that the situation will become worse. Few
dumps are expected.• MKI UFOs: MKI UFO Storms might be critical (but observed
storms disappeared again). Large effort underway to understand mechanism, in lab and in LHC.
• Beyond 2011:• Observations show an aggressive scaling with beam energy!
Situation could be significantly worse above 3.5TeV. Intermediate energy step would be very helpful for extrapolations to nominal energy.
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Next Steps
• MKI UFO MD (28.08.).• Study MKI/MKQA UFOs with improved diagnostics and better statistics.• Study dust particle dynamics.
• Improve diagnostics (during next TS).• Dedicated turn-by-turn BLM Study Buffer.• Improved BLM data logging.
• FLUKA simulations on MKI UFOs.• Open MKI and search for dust particles.• Dust particle dynamics model.• Better understanding of Quench Limit.
• Mitigation: Further increase of BLM thresholds...But: Do we have enough margin at higher energies?
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Summary and Conclusion
• 17 beam dumps due to UFOs in 2011 so far (18 in 2010).
• Over 10000 candidate UFOs below threshold detected. On average 6.0 UFOs/hour during stable beams in the arcs.Micrometer sized macroparticles are the most plausible explanation.
• Many UFOs around injection kicker magnets.Many MKI UFOs observed directly after kicker pulsing/injection.
• Observations show an aggressive scaling with beam energy! Situation could be significantly worse above 3.5TeV.
Intermediate energy step would be very helpful for extrapolations tonominal energy.
• Large effort underway to understand UFO mechanism.Measurements in LHC, lab measurements, simulations, theories.