1. Overview of LHC Beam Loss Measurements
Eva Barbara Holzer for the BLM team
CERN, Geneva, Switzerland
IPAC 2011
Bernd Dehning, Mateusz Dabrowski, Ewald Effinger, Jonathan Emery, Eleftherios Fadakis,
Eva Barbara Holzer, Stephen Jackson, Grzegorz Kruk, Christoph Kurfuerst, Aurelien Marsili,
Marek Misiowiec, Eduardo Nebot Del Busto, Annika Nordt, Agnieszka Priebe, Chris Roderick, Mariusz Sapinski, Christos Zamantzas, (CERN, Geneva),
Viatcheslav Grishin (CERN, Geneva and IHEP Protvino, Protvino, Moscow Region),
Erich Griesmayer (CIVIDEC Instrumentation, Wien)
Beam loss measurements of the LHC.
The emphasis of my talk is not on the protection functionality of the system, but on the data published by the BLM system. This data is used for various operational verifications; both online and offline.

2. Content Introduction to the BLM system Data published for
Logging display
Online and offline analysis
Fast (ms-time-scale) losses, UFO: Unidentified Falling Object
BLM Thresholds and Magnet Quench Levels
BLMs and Collimation
Betatron Collimation Loss Patterns
Tertiary collimator losses and Luminosity
Especially I will give you 4 examples of the usage of data published by the BLMs.

3. Introduction to the BLM System
But first a quick introduction to the BLM system.

4. Beam Loss Measurement System Layout
Main purpose: prevent damage and quench
3600 Ionization chambers (IC) interlock (97%) and observation
300 Secondary emission monitors (SEM) for observation
The main purpose is to avoid magnet quenches and damage to components by initiating a beam abort.
3600 ICs are installed and 300 SEMs. Here you see the inside of an ionization chamber with parallel plate electrodes in nitrogen gas. Below the inside of a SEM: 3 titanium electrodes in vacuum. Here you see how the monitors are installed outside of the magnet cryostats. The front-end electronics is installed in the tunnel; there is optical signal transmission to the surface electronics, which is connected to the beam interlock system.

5. Integration Times and Beam Abort Thresholds
12 integration intervals: 40μs (≈1/2 turn) to 84s (32 energy levels)
Each monitor (connected to interlock system BIS) aborts beam:
One of 12 integration intervals over threshold
Internal test failed
Stored Energy
Beam 7 TeV
2 x 362 MJ
2011 Beam 3.5 TeV
up to 2 x 100 MJ
Magnets 7 TeV
10 GJ
Collimator: 1p – 1E-12 Gy
Cold magnet: 1p – 1E-13 Gy
Arc: 1E9 p in 40us
Nominal: 3E14p
Quench and Damage at 7 TeV
Quench level
≈ 1mJ/cm3
Damage level
≈ 1 J/cm3

6. 4 Diamond BLMs for High Time Resolution
ATS/Note/2011/048 (TECH), B. Dehning et al.
Chemical Vapour Deposition (CVD) diamond for observation
Betatron collimators (one per beam)
All sizable local losses also seen at collimators
Injection regions (one per beam)
In addition to that system, there are 4 diamond loss monitors installed for high time resolution measurements. 2 are installed at the betatron collimators. At these aperture restrictions, all losses can be detected - even if they are far away and very localized. And two for injection losses in the injection region.

7. BLM Published Data – Logging Data
Extensively used for operation verification and machine tuning
Logging once per second (all 12 integration intervals)
Integration times < 1s: maximum during the last second is published
 short losses are recorded and loss duration can be reconstructed (20% accuracy for UFOs)
The so called logging data is published once a second. For integration times of less than 1 second, the maximum value during the last second is published. This was also very short losses are recorded and even the duration of a short loss can be approximately reconstructed.

8. BLM Published Data – Logging Data
Logging Data also used for Online Display
This data is also used for online display. Here you see an example: The loss signals for all the ring in green and in red the abort thresholds. By clicking on a monitor, the second window shows up, with all the 12 integration times of one monitor – the losses in green and the thresholds in red.

9. BLM Published Data – Event triggered Data Buffers
Event triggered BLM Data (40μs, 80μs or 2.6ms):
CVD Diamond high resolution loss data (2ns):
BLM Buffer (IC & SEM
Integration Time
Buffer Length
Post Mortem
40μs
80ms online 1.72s offline
Collimation Buffer
2.6ms
80ms
Extraction Validation Buffer
Capture Data
( 2 modes)
Injection Quality Check (IQC) – 8 crates only
20ms
Study (event triggered: for example UFO study)
80μs
Dynamical, currently up to 350ms
On top of this there are data buffers which are read out on request. For the standard system, I like to mention two: the post mortem buffer is read out after each beam abort and holds the 40us integral data. A special study capture buffer is used for the UFO analysis – it holds 80us integration data.
The diamond BLMs give post mortem data as well, with an integration time of approximately 2ns.
Event triggered
Sampling Rate
Integration Time
Buffer length
Post Mortem
0.2 ns
≈ 2ns
1ms

10. Fast (ms-time-scale) Losses UFO: Unidentified Falling Object
MOPS017  Simulation Studies of Macro-particles Falling into the LHC Proton Beam, F. Zimmermann et al.
TUPC136  Analysis of Fast Losses in the LHC with the BLM System, E. Nebot et al.
TUPC137  UFOs in the LHC, T. Baer et al.
Now to the Fast Losses. There are 3 papers at this conference about them. The first one is about simulations, the other two about loss measurements.

11. Beam Aborts due to UFO’s
Fast and localized losses all around the ring believed to be caused by macro particles intercepting the beam
Stepwise increase of BLM thresholds at the end of 2010 run
New BLM thresholds on cold magnets for 2011 start-up
Always detected by > 6 local monitors and at all aperture limits (collimators)
most UFOs far from dump threshold
UFO Beam Aborts 35
of which:
2010 17
2011 18
Around injection kickers (MKI) 13
Experiments 6
At 450 GeV 1
There have been 35 beam aborts due to UFOs, 17 in 2010 and 18 in 2011.

12. Gaussian Fit to UFO Time Distribution
PhD thesis T. Baer
Here you see a UFO time distribution; typically a gaussian fits the signal very well.

13. Diamond BLM Signals 3/10/2010 12h48, 152 bunches, 150ns bunch spacing
Here is a UFO as seen by the diamond BLMs at the collimators. The next plot show successive zooms into this signal.

14. Diamond BLM Signals 3/10/2010 12h48, 152 bunches, 150ns bunch spacing
Here you see the comparison between the diamond and the IC BLM signal – they match very well.

15. Diamond BLM Signals 3/10/2010 12h48, 152 bunches, 150ns bunch spacing
The bunch trains within one turn.

16. Diamond BLM Signals 3/10/2010 12h48, 152 bunches, 150ns bunch spacing
8 bunches per train.

17. Diamond BLM Signals 3/10/2010 12h48, 152 bunches, 150ns bunch spacing

18. UFO Duration 2010 and 2011 E. Nebot
Average duration: 130 μs at nominal intensity
Average maximum signal ≈ Gy/s
Estimate on signal increase at 7TeV compared to 3.5 TeV (from wire scanner measurements): factor 2 – 3.5
The UFOs are getting shorter with increasing beam intensity. The average duration at nominal intensity is 130us. The maximum signal does not depend on intensity
Protons / beam

19. BLM Thresholds and Magnet Quench Levels
WEPC172  Beam-induced Quench Test of LHC Main Quadrupole, A. Priebe et al.
WEPC173  LHC Magnet Quench Test with Beam Loss Generated by Wire Scan, M. Sapinski et al.

20. Quench Test: Wire Scanner Induced Losses
BLM signal deviation from Gaussian: wire vibrations, sublimation of 50% of wire diameter (from 34 μm to about 18 μm)
Voltage drop over the magnet coil (drop below zero due to signal disturbance)

21. Showers on Magnet from Losses on Collimator
Maximum voltage drop on superconducting magnet coil scales with BLM signal

22. Beam Loss Patterns Decomposing losses into known scenarios
TUPC141  LHC Beam Loss Pattern Recognition, A. Marsili et.al.
Losses on Tertiary Collimators and Luminosity

23. Decomposition of Losses
PhD A. Marsili
Loss patterns at Betatron Collimation from
Collimation cleaning verification measurements (‘loss maps’): Transverse blow-up by resonance crossing

24. Decomposition Prelim. Results
PhD thesis A. Marsili
Physics beams in collision, 1 point per second

25. Losses on Tertiary Collimators (TCT) and Luminosity
TCTs (protect final focus magnets)
Collimation losses scale with LHC luminosity
Left of Alice  additional losses after last technical stop
Cumulative Dose [mGy]
‘Stable Beam’ Periods June- Aug. 2011
Fill Number

26. Dose divided by Integrated Luminosity at Atlas TCT
Dose/Integrated Luminosity [mGy/nb-1]
‘Stable Beam’ Periods >2h June- Aug. 2011

27. Summary

28. Four Examples of the usage of BLM data:
Summary
Four Examples of the usage of BLM data:
Analysis of fast ms-time scale local losses (UFOs)
Analysis of magnet quench levels vs beam losses
Measurement of magnet coil voltage drop
Beam Loss Pattern recognition at collimators
Fill to Fill variations of losses