UFOs in the LHC

LHC Beam Operation CommitteeJune, 14th 2011 1

UFOs in the LHC

Tobias BaerLBOCJune, 14th 2011

Acknowledgements: N. Garrel, B. Goddard, E.B. Holzer, S. Jackson, M. Misiowiec, E. Nebot, A. Nordt, J. Uythoven, J. Wenninger, C. Zamantzas

2LHC Beam Operation CommitteeJune, 14th 2011

Content

1. UFO Dumps

2. Below Threshold UFOs

3. UFOs at MKIs

4. Outlook


Content

1. UFO Dumps


3. UFOs at MKIs

4. Outlook


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 GeV. (6.6.2011)


Content

1. UFO Dumps


3. UFOs at MKIs

4. Outlook


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 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 (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.


Events Below Threshold

“threshold” = lowest threshold in standard arc cell.

Most events are much below threshold.

nom

inal

thre

shol

d 7

TeV

628 candidate UFOs at 3.5 TeV.Signal RS05 > 5∙10-4 Gy/s.


Spatial UFO Distribution

3.5 TeV1096 candidate UFOs.

Signal RS05 > 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.

gray areas around IRs are excluded from UFO detection.

450 GeV591 candidate UFOs.

Signal RS05 > 5∙10-4 Gy/s.

Mainly UFOs around MKIs

NICE

significant increase at MKI.R8


On average: 10 UFOs/hour

UFO Rate in 2011

1904 candidate UFOs during stable beams. Signal RS05 > 2∙10-4 Gy/s. Data scaled with 1.76 (detection efficiency from reference data)

228

b 3

6 bp

i

336b

36

bpi

336b

72

bpi

480b

36

bpi

336b

72

bpi

480b

36

bpi

480b

72

bpi

624b

72

bpi

768b

72

bpi

228

b 3

6 bp

i48

0b

72 b

pi76

8b

72 b

pi76

8b

108

bpi

912b

10

8 bp

i

1092

b 1

08 b

pi

1092

b 1

44 b

pi


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


Loss Duration

• Tloss: Given by fitting single function (Gaussian up to t=Tloss, 1/t afterwards) to data.

• Loss duration: UFOs have the tendency to become faster with increasing intensity.

(cf. E.B. Holzer at Evian Dec. 2010)

courtesy ofE. Nebot


Peak Signal vs Loss Duration

Tendency that harder UFOs are faster.courtesy of

E. Nebot


Content

1. UFO Dumps


3. UFOs at MKIs

4. Outlook


Beam dump on 6.6.2011

UFO at MKI in Pt. 2, at 450 GeV.

MKIs

TCT


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)

(cf. T. Baer 86th LMC)


Peak Losses

Peak loss for MKI UFOs at 450 GeV.Threshold (RS1 = 2.3 Gy/s)

336 candidate UFOs at 450 GeV. Signal RS01 > 2∙10-4 Gy/s.

+ 1 event with 3.5Gy/s (dump 06.06.2011)


UFOs around Injection Region

• 679 UFOs around the MKIs caused 9 beam dumps.

Most of the UFOs around the MKIs occur before going tostable beams.


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


UFOs at MKIs per fill

Flashover of MKI D Pt.8 before Fill 1721 (vacuum valves moved in).

Fill 1721:21 MKI UFOs in Pt.82 MKI UFOs in Pt.2

Flas

hove

r


Correlation with Vacuum

Despite a large vacuum spike, there is no clear correlation with UFOs


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


Content

1. UFO Dumps


3. UFOs at MKIs

4. Outlook


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.


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 TeV.UFO rate constant at 10 UFOs/hour at 3.5 TeV.

• Many UFOs around injection kicker magnetsDuring scrubbing: increased UFO rate after each injection.Increased UFO rate after MKI Flashover.

• Next steps: UFO MD, Improve the diagnostics, better understanding of quench limits, learn from simulations.


Thank you for your Attention

Tobias BaerCERN BE/[email protected]: +41 22 76 75379

Further information:• T. Baer, “UFOs in the LHC”, Joint DESY and University of Hamburg

Accelerator Physics Seminar, May 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.


Backup slides


UFOs in 2010

• 18 beam dumps due to UFOs.(since 07.07.2010)

• 113 UFOs below threshold foundin logging database. (E. Nebot)

(03.08.2010 - 28.10.2010)

• 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)

J. W

enni

nger


Event Rate

• 113 events below threshold found in 2010. (E. Nebot)

• UFO rate: proportional tobeam intensity.

courtesy ofE. Nebot


Calibration of Tloss

Correlation of Tloss and width of Gaussian fitted topost mortem turn-by-turn data.courtesy of

E. Nebot


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.


UFO Algorithm

1. Losses (RS 4) of at least two BLMs within 40m are above 1E-4 Gy/s.

2. A BLM is not taken into account ifIt is at a TCTIt is in IP3, IP6 or IP7RS 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.


LHC UFO Buster

LHC Console Manager -> Fixed Displays -> BLM -> UFO Buster


UFO Detection

• For 2010: 113 UFOs below threshold found in logging database. (E. Nebot)

• For 2011: Online UFO detection by UFO Buster.Detects UFOs in BLM concentrator data (1Hz).

• 5000 UFOs below threshold foundso far.

Most events are much below threshold.

“threshold” = lowest threshold in standard arc cell.

nom

inal

arc

th

resh

old

7 Te

V

4905 candidate UFOs at 3.5 TeV.


Dump on 01.05.2011

Dump of BLMQI.04L2.B1E20_MQY on RS 3, 4 and 5

Dump of BLMQI.04L2.B1E20_MQY on 320µs, 640µs and 2.5ms integration time


Dump on 01.05.2011

• From fit to losses (BLMEI.05L2.B1E10_MKI.D5L2.B1):

Amplitude: 0.63 Gy/sWidth: 0.29 ms


Correlation with Vacuum


Dynamics of Dust Particles

From simulations:

• Dust particle will be positively ionized and be repelled from the beam.

Beam intensity: 2.3 10∙ 12 protons, Al object.

• Loss duration of a few ms.Losses become shorter for larger beam intensities.

courtesy ofF. Zimmermann


Correlation with Wire Scanner

From wire scans: linear dependency of BLM signal on beam energy

courtesy ofM. Sapinski (cf. Chamonix 2011)


Layout of MKI Region


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)


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 fr

ee fa

ll

εnorm = 2.5 µm·radβ = 150 m

sm

U hgv 63.02


Known Dust Particle Sources

• Distributed ion pumps (PF-AR, HERA).

• Electrical Discharges (PF-AR).

• Movable Devices.

• Particles frozen or condensated at cold elements. (ANKA)

Documents

UFOs in the LHC