UFOs or ‘Unidentified Falling Objects’ have apparently been causing problems in the form of mysterious rapid beam dumps at the Large Hadron Collidor (LHC). It is not yet known definitely what is causing these UFOs and even exactly what they are. One as yet unproven hypothesis is that they are dust particles falling into the beam path and triggering a beam dump. Studies have shown they occur primarily at the injection points shortly after injection, often but not always creating problems before the LHC beams have become stable.

There had been over 5000 below threshold UFO events by June 2011, yet surprisingly, at that time their frequency was not increasing with further intensity advances. Possible sources of these hypothetical dust particles include distributed ion pumps, electrical discharges, movable devices and articles frozen or condensated at cold elements. Simulations suggest that these hypothetical dust particles are also positively ionized and repelled from the beam.

As a laywoman who is very interested in the recent reports of hypothetical superluminal neutrinos being produced by the LHC and measured by OPERA at Gran Sasso, I was quite fascinated to read a report about these UFOs at the LHC on viXra several months ago, which contained links to a powerpoint of a detailed June 2011 UFO report from the CERN LHC Beam Operating Committee.

In September 2011, another quite technical Powerpoint report from J. Wenninger at CERN’s LHC Beams Department Operation group,  provided an update of the latest UFO research findings see http://jwenning.web.cern.ch/jwenning/documents/LHC/Talks/LHC.PAF.Sep11.ppt however, I was hoping that more layperson reader friendly scientific information, would have become more generally available on the Internet by now, so hopefully writing this blog will help to bring this about, in the meantime here is a quite detailed scientific paper describing the UFO's in the LHC.

LHC Operation Challenges
Wikipedia describes some of the huge Large Hadron Collider's  ‘operational challenges’. :-

'The size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account of the amount of energy stored in the magnets and the beams. While operating, the total energy stored in the magnets is 10 GJ (equivalent to 2.4 tons of TNT) and the total energy carried by the two beams reaches 724 MJ (173 kilograms of TNT).’‘Loss of only one ten-millionth part (10−7) of the beam is sufficient to quench a superconducting magnet, while the beam dump must absorb 362 MJ (87 kilograms of TNT) for each of the two beams. These energies are carried by very little matter: under nominal operating conditions (2,808 bunches per beam, 1.15×1011 protons per bunch), the beam pipes contain 1.0×10−9 gram of hydrogen, which, in standard conditions for temperature and pressure, would fill the volume of one grain of fine sand.’

The ViXra Log
The Vixra log website claims to provide news about science in general and also reports on large scientific experiments, plus articles on unusual episodes from the history of science and mathematics. Earlier this year in February 2011 this viXra log reported that :-

‘The Large Hadron Collider’s cryogenic systems have now cooled down all the superconducting magnets to 1.9 degree Kelvin as required for this year’s physics runs. This means that the main accelerator ring is essentially ready for beam injection which is scheduled to start on 21st February.’‘The plan will be to bring the collider back to last years peak luminosity of 0.2/nb/s as quicky as possible so that the experiments can start to add significant data to what they have already collected. The bunch spacing used will be 75 ns instead of the 150 ns used before. With this closer packing it should be possible to circulate about 900 bunches in each beam to more than double the beam intensity. Further luminosity increases will be achieved with a tighter squeeze of the beams at the collision points.'

'Overall they hope to slowly progress towards 1.0/nb/s luminosity then just work on maximum running efficiency.’ ‘Some problems identified towards the end of last year will have to be dealt with. This includes Unidentified Falling Objects in the beam pipe and a build up of electron clouds. To clean the pipes they will “scrub” with extra high intensity beams at lower energy using 50ns spacing to pack in even more bunches. As last year, the proton physics operations will end in November to allow time for some more heavy ion collisions. This year they will aim for a significant increase in luminosity for these collisions. At the end of the extended proton physics run in 2012 they may try out collisions of protons on heavy ions. As last year we plan to closely follow the progress on viXra Log.’

Then this Vixra log reported that :-

‘In his talk Myres gave some more information about UFOs. These are mysterious rapid beam loss events thought to be caused by particles falling into the beam path. They can trigger the protection mechanisms to dump the beams. Studies have shown that they most often occur at the injection points and almost always shortly after injection causing problems before they get to stable beams. Surprisingly their frequency is not increasing with further intensity advances. They were 110 of these UFO events last year and already 5000 this year, but only the strongest cases can trigger a beam dump.’

The CERN LHC Beam Operating Committee Powerpoint Report on UFOs
A detailed powerpoint report on these UFOs dated June 2011 from the CERN LHC Beam Operating Committee authored by Tobias Baer contains many interesting statistical graphs and diagrams, detailing extensive research into these LHC UFOs, including some of the following information and summaries:-

UFO Dumps
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•       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)

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 areabove 1E-4 Gy/s.
           
RS 2 / RS 1 > 0.55 (UFO average :0.89).
            RS 3 / RS 2 > 0.45 (UFOaverage: 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

Spatial UFO Distribution

On average:10 UFOs/hour

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.

•       Loss duration:UFOs have the tendency to become faster with increasing intensity.
                               (cf. E.B. Holzer at Evian Dec. 2010)

Peak Signal vs Loss Duration

Tendency that harder UFOs are faster.

Beam dump on 6.6.2011

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

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

•        Amplitude:7.73 Gy/s

                        (Threshold: 2.3 Gy/s)

•        Width:0.77 ms

            resulting speed of transiting dust particle  = 0.47 m/s. (assuming ϵn=2.2µm·rad)

Peak Losses

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

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

Peak loss for MKI UFOs at 450 GeV.

Threshold (RS1 = 2.3 Gy/s)

UFOs around Injection Region

•       679 UFOs aroundthe MKIs caused 9 beam dumps.

            Most of the UFOs around the MKIs occur before going to stable 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.

UFOs at MKIs per fill

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

Correlation with Vacuum

Despite a large vacuum spike, there is no clear correlation with UFO's 

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:

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 June 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 magnets
            During 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.

UFOs in 2010

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

•       113 UFOs below threshold found in 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. Holzerat Evian Dec. 2010)

•       Loss duration has tendency to become faster with higher intensity. (cf. E.B. Holzerat Evian Dec. 2010)

Event Rate

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

•       UFO rate: proportional to beam intensity.

Calibration of Tloss

Correlation of Tloss and width of Gaussian fitted to post mortem turn-by-turn data.

Fast Loss Event Rate

•       After the increase of the BLM Threshold by a factor of 3 there were about 4.1times 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 if

 It is at a TCT

It is in IP3, IP6 or IP7

RS 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 found so far.

           Most events are much belowthreshold.

 4905 candidate UFOs at 3.5 TeV.

“threshold”= lowest threshold in standard arc cell.

Dump on 01.05.2011

Dynamics of Dust Particles

From simulations:

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

Beam intensity: 2.3∙1012 protons, Al object.

•       Loss duration of a few ms.

Losses become shorter for larger beam intensities.

Correlation with Wire Scanner

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.

UFO Speed

The UFO speed corresponds to the expected speed for a free fall from the aperture.

Known Dust Particle Sources

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

•       Electrical Discharges (PF-AR).

•       Movable Devices.

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

The additional information about the LHC UFOs that I was able to glean from the more recent September report from CERN was in summary :-

'Very fast beam loss events in super-conducting regions of the LHC were THE surprise of 2010 –nicknamed UFOs (Unidentified Falling Object).

Beam dumps triggered by UFO events:

18 beam dumps in 2010,

11 beam dumps in 2011, last beam dump mid-July 2011.

All but one dump at 3.5 TeV.

Things are‘calming down’ at 3.5 TeV, but the situation is worrying for future 7 TeV operation: Extrapolation to 7 TeV predicts ~ 100 dumps / year.

Due to lower quench thresholds and larger deposited energy density.

UFO Rate ~slowly decreasing to ~ 3-4 / hour 

Most likely hypothesis for UFO: small ‘dust ‘ particle falling into the beam

UFO loss amplitude distribution is consisted with measured dust particle distributions in the assembly halls…

The UFOs are distributed around the machine. About 7% of all UFOs are around theinjection kickers.

Mainly UFOs around injection kickers (MKI) 

We are focusing on the understanding of UFO at the MKIs

Detailed FLUKA model of the injection region to reproduce UFO losses and help localizing the source(s).

Spare MKI that was removed from the LHC last year will be opened for dust analysis.'