ufos observations, statistics and extrapolations

Evian Workshop 2012December, 19th 2012 1

UFOsO b s e r va t i o n s , S t a t i s t i c s a n d E x t ra p o l a t i o n s

Evian Workshop 2012Tobias BaerDecember, 19th 2012

Acknowledgements: V. Baglin, M.J. Barnes, S. Bart Pedersen, F. Cerutti, F. Day, B. Dehning, L. Ducimetière, E. Effinger, A. Ferrari, N. Fuster Martinez, N. Garrel, A. Gerardin, B. Goddard, E. Griesmayer, M. Hempel, E.B. Holzer, S. Jackson,

M.J. Jimenez, V. Kain, A. Lechner, V. Mertens, M. Misiowiec, R. Morón Ballester, E. Nebot del Busto, A. Nordt, M. Sapinski, R. Schmidt, J. Uythoven, V. Vlachoudis, J. Wenninger, C. Zamantzas, F. Zimmermann, …


Content

1. UFO Observations and Statistics

2. MKI UFO Observations

3. Extrapolation for after LS1

4. Mitigation Strategies and Outlook


Content






In 2012: 20 beam dumps due to (Un)identified Falling Objects.

2011: 17 dumps, 2010: 18 dumps.14 dumps at 4TeV, 3 during ramp,

3 at 450GeV.8 dumps by MKI UFOs, 4 by UFOs around collimators during movement (TCL.5L5.B2, TCSG.4L6.B2)4 by ALICE Ufinos.

≈ 17,000 candidate UFOs below BLM thresholds found in 2012

2011: about 16,000 candidate UFOs.

Introduction

Diamond BLM in IR7

Spatial and temporal loss profile ofUFO at BSRT.B2 on 27.08.2012 at 4TeV.

B1B2

UFO location

200mPt. 4


Loss Duration

BLM Study Buffer provides for all BLMs temporal loss profile with 80µs resolution (350ms buffer length).

Average temporal width of 4TeV arc UFOs has maximum at about 80µs.

May become faster with smaller emittance at higher energies.

683 arc (≥ cell 12) UFO events at 4TeV with 1374/1380 50ns bunches. Signal RS04 > 2∙10-4 Gy/s. Peak loss (fit) > 1∙10-3 Gy/s. Only datasets with R² ≥ 0.97. Data is corrected for BLM time response.

Risetime: 212µs

Falltime: 92µs


2011: Decrease from ≈10 UFOs/hour to ≈2 UFOs/hour.2012: Initially, about 2.5 times higher UFO rate than in

October 2011. UFO rate decreases since then.Up to 10 times increased UFO rate with 25ns.

Arc UFO Rate

9966 arc UFOs (≥ cell 12) in 393 fills during stable beams between 14.04.2011 and 6.12.2012. Fills with at least 1 hour stable beams are considered. 25ns fills at 4TeV are also considered. Up to 5 consecutive fills with the same number of bunches are grouped. Signal RS04 > 2∙10-4 Gy/s. In 2012 only UFOs with Signal RS3/Signal RS2 0.45 to correct for algorithm changes.


Content






MKI UFOs• In 2012: 8 dumps by MKI UFOs (5 at 4TeV).

2011: 11 dumps by MKI UFOs (2010: 2)2012: 6 dumps from MKI.D5L2 (since 2010:

17).

• During MKI inspection in 2011 many macro particles were found, which are believed to originate from Al2O3 ceramic tube.

Typical macro particle diameter: 1-100µm.

• Temporal distribution:Mainly within 30min after last injection.

Many events within a few hundred ms after MKI pulse. (T. Baer et al., CERN-ATS-Note-2012-018

MD)

• Positive correlation between MKI UFO rate and pressure in MKI tank at 450 GeV.

(T. Baer et al., CMAC #6)

0 2 4 6 8 10Energy (keV)

0

20

40

60

cps

C

O

Al

AuAu

Al

O

A. Gerardin, N. GarrelEDMS: 1162034

1024 MKI UFOs until 6.12.2012. in 1374b/1380b physics fills with at least 3 hours after the last injection. Signal RS04 > 2∙10-4 Gy/s.


Decrease from about 8 MKI UFOs per fill with 1380b in 2011 to about 2 MKI UFOs per fill.No increased activity for 25ns 4TeV fills (with intermediate intensities).

MKI UFO rate

2375 MKI UFOs in fills with stable beams and at least 3 hours at flattop energy between 14.04.2011 and 6.12.2012. Additionally, 25ns fills with 4TeV are considered. Up to 4 consecutive fills with same number of bunches are grouped. Signal RS04 > 2∙10-4 Gy/s. In 2012 only UFOs with Signal RS3/Signal RS2 0.45 to correct for algorithm changes.


Most MKI UFOs occur at MKI.D5L2. UFO activity at MKI.D5R8 (replaced during TS#3: improved cleaning,

reduced electrical field) after TS#3 (72 ±11)% lower. In the other IR8 MKIs, UFO activity decreased by (32 ±12)%.

MKI UFO Distribution

145/52 UFOs around MKIs in IR2 in 159/77 fills with stable beams and at least 1000 bunches before/after TS#3. Signal in RS4>5·10-4.

Beam 1 Beam 2

194/52 UFOs around MKIs in IR2 in 159/77 50ns fills with stable beams and at least 1000 bunches before/after TS#3. Signal in RS4>5·10-4. Slightly different BLM positions since TS#3 may slightly perturb the analysis.

- 32% -72%

replaced in TS#3


Content






25ns Observations

Observations from 2012 operation with 25ns:• During high intensity fills at 4TeV about 5-10 times increased arc

UFO activity.Particularly high arc UFO rate in first fills (3427-3429).

• Between 13.12.2012 and 17.12.2012: 10 UFOs above 10% of BLM dump threshold.Largest UFO 67% of BLM dump threshold.

• During 450GeV scrubbing run: In total 221 MKI UFOs in 13 fills with > 1014 protons ≈ 17 MKI UFOs per fill.

For 50ns ≈2 MKI UFOs per fill.

• No increased MKI UFO rate in 25ns 4TeV fills.


Quench Margin 2012

Largest arc UFO in 2012: 0.67mGy at BLM 2 (5.10.2012 06:19:41).

Assume that UFO occurred at Pos #2 (i.e. close to the MQ):

From FLUKA simulations (for 3.5 TeV): ≈1.3·108 inelastic interactions needed to explain BLM signal.

(A. Lechner at QTSWG, 04.05.2012)

Peak energy density in MB.C: ≈3.9 mJ/cm³.

Simulations by A. Lechner and the FLUKA team


Quench Margin at 7TeV

For UFO at Pos #1 with ≈1.3·108 inelastic interactions:

at 3.5TeV: ≈7.8 mJ/cm³.at 7.0TeV: ≈32.5 mJ/cm³.

For 3.5TeV: About a factor 4 below QP3 quench margin.

For 7TeV: About a factor 10 - 20 (QP3/Note44) above quench

margin. FLUKA simulations for UFO at Pos #1.

x 4.2

Simulations by A. Lechner and the FLUKA team

QP3

Note44ZERODEE

M. S

apin

ski

QP3

Note44ZERODEE

M. S

apin

ski


Extrapolation to 7 TeV:BLM signal/threshold (based on Note44) is for arc UFOs about 20 times larger than at 3.5 TeV.

Based on 2012 arc UFOs:91 UFO related beam dumps.(based on 2011: 112 dumps)

Additionally, 21 beam dumps by MKI UFOs (2012 data, full cycle). (based on 2011: 27 dumps)

Additionally (not considered): UFOs around IRs until cell 11, at collimators/movable devices and Ufinos in experiments.

Energy Extrapolation

Based on the applied threshold table from 10.12.2012. For MKI UFOs, only the BLMs at Q4 and D2 are considered. The energy scaling applies only to events at flat top, but (for MKI UFOs) the full cycle is taken into account for the extrapolation. Apart from the beam energy, identical running conditions as in 2011/2012 are assumed. In particular not not included are: margin between BLM thresholds and actual quench limit, 25ns bunch spacing, intensity increase, beam size, scrubbing for arc UFOs, deconditioning after LS1.


Content






MKI UFO Mitigations

Improvements of all MKIs:

• NEG coating of interconnects, by-pass-tubes and BI equipmentMitigation of electron-cloud.

Improved vacuum in MKI.

• Improved cleaning procedureReduced initial dust contamination.Additional cleaning after insertion of metal wires.

• Up to 24 screen conductors on all MKIsReduced electric field during MKI pulse.

• Coating of ceramic tube (under investigation, max. 1 MKI).Reduced SEY and surface charging.Two options under consideration: carbon and Cr2O3. (cp. EDMS Doc. No.

1235378)


Arc UFO Mitigations

• Increase BLM thresholds towards the quench limit.

• UFO scrubbing.

• Optimized BLM distribution for better protection against arc UFOs.

(M. Sapinski at MPP, 12.10.2012)

• ADT fast-losses quench test.Better understanding of quench

margin.

-> see presentation by Eduardo

A. Lechner


Summary• 20 beam dumps due to UFOs in 2012.

• Temporal width typically 50-200µs.May be too fast for active protection with smaller emittance at higher

energy.

• Arc UFO rate at beginning of 2012 ≈2.5 times higher than in October 2011. Arc (and MKI) UFO rate decreases since then.

• Energy extrapolation to 7 TeV: 2011 arc and MKI UFOs would have caused 139 beam dumps.2012 arc and MKI UFOs would have caused 112 beam dumps.

• About 5-10 times increased UFO activity with 25ns.

• Mitigations: For MKI UFOs, different mitigations are in preparation. Observations with

improved MKI.D5R8 look promising.

For Arc UFOs, optimized BLM distribution allows a better UFO protection.


Thank you for your Attention

Tobias BaerCERN BE/[email protected]

Further information:• E. Nebot del Busto et al., “Detection of Unidentified Falling Objects at the

LHC”, HB2012, TUO1C04.

• T. Baer et al., “UFOs in the LHC: Observations, Studies and Extrapolations”, IPAC’12, THPPP086.

• B. Goddard et al., “Transient Beam Losses in the LHC Injection Kickers from Micron Scale Dust Particles”, IPAC’12, TUPPR092.

• A. Lechner et al., “FLUKA Simulations of UFO-Induced Losses in the LHC Arc“, Quench Test Strategy Working Group.

• T. Baer et al., “UFOs in the LHC after LS1”, Chamonix Workshop 2012.

• T. Baer et al., “UFOs in the LHC”, IPAC’11, TUPC137.

• N. Fuster et al., “Simulation Studies of Macroparticles Falling into the LHC Proton Beam”, IPAC’11, MOPS017.


Content

Backup slides


• Distribution in 2011 and 2012 is very similar.

• In 2012 larger fraction of MKI UFOs.

• Some arc cells with significantly increased number of UFOs:

19R3 B1, 25R3 B2, BSRT B2, 31L7 B2, 28R7 B2, 28L8 B1…

No direct correlation with sector 34 repairs identified.

Spatial UFO Distribution

MKI

MKIAdditional BLMs in cell 19R3

2011: 7409 UFOs at 3.5 TeV.2012: 6922 UFOs at 4TeV until 6.12.2012.Signal RS04 > 2∙10-4 Gy/s.Gray areas around IRs are excluded from the analysis.

BSRT

407

332


UFOs in cell 19R3

• Additional BLMs in cell 19R3 to determine UFO location.

19R3 19R3

19R319R3

19R3

UFOs with different spatial loss pattern were observed in cell 19R3, suggesting that the UFOs originate from various position across the cell.

cp also A. Lechner et al., Quench Test Strategy Working Group, May 2012


No significant change of UFO rate throughout a fill.

Intrafill UFO rate

4952 arc UFOs (cell 12) between 14.04.2011 and 6.12.2012 during stable beams in 114 fills with at least 10 hours stable beams. Signal RS04 > 2∙10-4 Gy/s.


• 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.

Below Threshold UFOs

courtesy of J. M. Jimenez

∝ 𝒙−𝟎.𝟗𝟕

4513 arc UFOs (≥cell 12) at 3.5 TeV with signal RS01 > 1∙10-3 Gy/s.


Intensity Dependency

For low intensities: UFO rate Intensity,saturates at high intensities.

consistent with previous analysis (cp. E. Nebot, IPAC’11).

500 candidate UFOs during stable beams with a signal in RS04 > 2∙10-4 Gy/s. 28 fills with at least 1 hour in stable beams in the first quarter of 2012 are considered. The beam intensity is computed as the maximum intensity per fill, averaged over both beams.


Falltime becomes faster than risetime for large loss amplitues.

Asymmetry vs. Loss Amplitude

683 arc (≥ cell 12) UFO events at 4TeV with 1374/1380 50ns bunches. Signal RS04 > 2∙10-4 Gy/s. Peak loss (fit) > 1∙10-3 Gy/s. Only datasets with R² ≥ 0.97. Data is corrected for BLM time response.

courtesy of F. Zimmermann, N. Fuster

IPAC’11: MOPS017

Simulated loss rate for different macroparticle masses. Beam intensity: 1.6·1014 protons.

Simulation Measurement


No significant correlation of UFO duration with loss amplitude.

UFO Duration vs. Amplitude

Risetime Falltime


UFO Rate vs. Emittance

UFO rate increases with normalized emittance.

courtesy of F. Day

Emittance from luminosity at start of stable beams.


UFO rate vs Bunch Intensity

No dependency of UFO rate on bunch intensity.

Data for 3336 candidate arc UFOs during stable beams in 2011 and 2012 (until 19.07.2012). Fills with 1374/1380 bunches and at least 1 hour of stable beams are considered. Signal RS04 > 2∙10-4 Gy/s.


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


4TeV Arc UFOs with 25ns

• With 50ns, 1374b: ≈ 1.3 arc UFOs per hour

• 13. – 17.12.2012: 10 UFOs > 10% of BLM dump thresholdLargest UFO: 67% of BLM dump threshold

Fill # bunches Time @ 4TeV [h:m] # arc UFOs UFOs/hour

3425 84 3:21 8 2.38 (±0.84)

3427 156 1:02 7 6.73 (±2.55)

3428 372 2:37 36 13.68 (±2.28)

3429 804 9:49 87 8.85 (±0.95)

3436 804 1:19 8 6.02 (±2.13)

3441 108 2:11 5 2.29 (±1.02)

3442 204 2:31 5 1.98 (±0.88)

3443 396 0:38 3 4.73 (±2.73)

3453 396 8:43 11 1.26 (±0.38)

3457 780 0:28 2 4.17 (±2.95)


Identified/Possible UFO Sources

• Movable Devices (roman pots, collimators).

• Ceramic particles from MKI tube.

• Distributed ion pumps (PF-AR, HERA), not in LHC arc.

• Macro particles frozen or condensated at cold elements.

• Sparking/Electrical Discharges (PF-AR).


UFO Model

Potentially charged by electron cloud

e-e-

e-Interaction with beam leads to positive charging of UFO. Particle could be repelled by beam

Local beam losses due to inelastic nuclear interaction.

ceramic tube

Beam

Metal strips for image currents

Al2O3 fragment of vacuum chamber.Size: 1-100µm.

Detaching stimulated by vibration, electrical field during MKI pulse and/or electrical beam potential.

19mm

• Implemented in dust particle dynamics model, which predicts (among others):

Loss duration of a few ms.Losses become faster for largerbeam intensities.

courtesy of F. Zimmermann, N. Fuster

IPAC’11: MOPS017

Beam loss rate as a function of time for different macroparticle masses. Beam intensity: 1.6·1014 protons.


• UFO amplitude: At 7 TeV about 4 times higher than at 3.5 TeV.

Arc UFO FLUKA Simulations

Courtesy of A. Lechner and the FLUKA team.

x4 At indicated longitudinal position for UFO at 7 TeV.Beam direction: out of screen.

For UFO at Pos #1


Positive correlation between pressure at MKI and MKI UFO rate.Similar indications also from scrubbing runs and 2012 UFO MD.

Vacuum Correlation

141 MKI UFOs in Pt. 8 between last injection of beam 2 and beginning of ramp for 178 fills with 1374/1380 bunches until 23.07.2012.

5.1σ statistical significance of positive correlation.


• 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)

UFOs after MKI Pulse

T. Baer et al., IPAC‘11, TUPBC137

T. Baer et al., CERN-ATS-Note-2012-018 MD


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.


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. Redaelli

EDMS: 1153686


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).

Horizontal dispersion

MKI (UFO location)

MQML.10L8 (highest loss)

IP8

TCTH


• Better localization of arc UFOs by mobile BLMs in cell 19R3.

• FLUKA simulations for arc UFOs.

• MadX simulations for UFOs.

• Better temporal resolution of UFO events (dust particle dynamics).80µs time resolution of BLM study buffer.Bunch-by-bunch diagnostics with diamond BLMs.

• Study impact of 25ns operation. 25ns high intensity (several 100 - 1000 bunches) beam for few hours at 4TeV.

• MKI UFO MD.25ns, e-cloud correlation, UFO production mechanism, particle dynamics.

• Better localization of arc UFOs by mobile BLMs in cell 19R3.

• FLUKA simulations for arc UFOs.

• Better temporal resolution of UFO events (dust particle dynamics).80µs time resolution of BLM study buffer.Bunch-by-bunch diagnostics with diamond BLMs.

• Study impact of 25ns operation. 25ns high intensity (several 100 - 1000 bunches) beam for few hours at 4TeV.

• MKI UFO MD.25ns, e-cloud correlation, UFO production mechanism, particle dynamics.

Plans for 2012

From Chamonix 2012scheduled, but due to many (unrelated) technical problems with limited success.

Courtesy ofM. Hempel

cp. LBOC, 24.07.2012

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