1. Verification of the Beam Loss studies at start-up
L. Ponce
Thanks to B. Dehning, M. Sapinski, S. Redaelli, R. Assmann, B. Holzer, BLM team, Collimation team, MPSCWG,... 1

2. Outlines Asked questions: Presentation of the simulations
Initial settings of the thresholds
Commissioning with beam
Changing thresholds
Asked questions:
Procedure for calibrating the loss patterns
Operational scenarios given measured BLM losses
Thresholds adjustment and masking disabling during operation 2

3. Preliminary remarks
Procedure for HW commissioning of the BLM system has been already presented by J-J. Gras
The detailed of the implementation of the system presented at the LTC
Procedure for collimator settings using BLM described by R. Assmann
Details of the sector test provoked quench also already presented by R. Assmann
MP functionalities of the BLM system is commissioned in phase A.5 (R. Jones and J. Uythoven talks)‏
this talk is more oriented to quench prevention functionality 3

4. 1. Details of the simulations
simulation needed for positioning of the BLM and for the thresholds generation
global loss pattern and local loss pattern 4

5. Proton/ion loss maps Protons (collimation team) :
scenarios: nominal settings, worst cases, error scenarios, injection and top energies, both beams
Ions (H. Braun, J. Jowet, G. Bellodi) : both beams
Protons in collimation areas
FLUKA simulations for IR7, triplets area, MARS for IR3
Protons: magnets failure scenarios (A. Alonso)
The complementary/redundant simulations allow a detailed view of particle loss locations

6. Two examples from G. Robert-Demolaize's talk in Chamonix 2006
▬► halo 6

7. Global loss patterns
systematic analysis of all the loss maps provided in order to identify the loss locations and place BLMs
BLMs at each quad, plus some extra locations:
on MBs in dispersion suppressor in IR3 and 7
SEM+ IC pairs at each coll to cover the dynamic range
MBs in DS and arcs for ions
on standalone dipoles in LSS
effect of the collimators settings is a global effect: peaks are moving from one quad to another, from an IR to another... The dominant effect is the loss in the following dispersion suppressor + ARC

8. “local” loss pattern
same typical pattern for losses at the element level:
Peak before MQ at the aperture limit
End of loss at the centre of the MQ (beam size effect)‏ 8

9. typical results of the simulations
Maximum of the shower ~ 1m after impacting point in material whatever the impacting angle and transverse position of the post protons
increase of the signal in magnet free locations
factor 2 between MQ and MB
20 % more in the peak amplitude by doubling the angle (typic mrad)‏
40 % less in peak amplitude between the uppermost/innermost impacting point
z (cm)‏ 9

10. Realistic “local” loss pattern
The 3 monitors at the quadrupoles will show a decreasing signal in beam direction
beam 2
Cross-talk signal 10

11. => a total of 4000 monitors (3600 IC + 400 SEM)‏
Positions of the BLM
3 BLM per beam at each quadrupoles
BLM in LSS : dipoles, collimators, warm magnets, MSI, MSD, MKD,MKB, all the masks…
=> a total of monitors (3600 IC SEM)‏
positions as much as possible “standardized” to limit the number of different thresholds
BLM grouped in families
family = same quench level and same material between the loss and the BLM)‏
250 families
Beam dump threshold set relative to quench level for cold elements or to the element damage level (need equipments experts to set the correct values) for warm element‏ 11

12. 2. thresholds generation12

13. Strategy to generate thresholds
Parameterisation LHC Proj Note 44
QL instant loss
calculation +
simulations
QL steady state loss
simulations + measurements
Quench level QL
N protons quench = QL/Ep
energy deposition in coil Ep
response function Q(F)‏
particle fluence F simulations
Threshold = Q(F)*Nprotons quench
simulation code: FLUKA or Geant4, quench level: D. Bocian code

14. Ingredients of the recipe
Threshold values contain :
the BLM response (electronics, chamber response calibration)
the position of the BLM relative to the cold masses,i.e amount of material to cross (BLM grouped by families)
the ratio between the lost protons and the BLM signal (particle shower simulation)
the ratio between the BLM signal and the deposited energy in the coil for the family (particle shower simulation)
the knowledge of quench level and/or the damage level (W/cm3)‏ (seeds for parametrization )
the dependence of the quench/damage level on beam energy and integration time. (for parametrization of the thresholds)‏
topology of the losses 14

15. Calibration of the detector response
calibration of all the chambers (HW commissioning)‏: all chambers are calibrated before installation + radiation source tests in situ
detector model checked with the CERN/H6 experiment (M. Stockner PhD thesis) plus proton, gamma and neutron measurements
measurements of the tails of the secondary shower with BLM on HERA dump : comparison with G4 simulation (M. Stockner)
radiation tests for SEE studies
=> well controlled, expected uncertainty < 50 % 15

16. Relative loss levels for fast / slow losses
Calibration of the quenches/damage level
quench tests campaign in SM18 for quench magnet model verification (steady state losses) (D. Bocian,A. Siemko)
damage level estimation : working group to re-visit the calculations
Dump threshold 1
Quench level
320 5
Damage level
7 TeV
450 GeV
Relative loss levels for fast / slow losses
Arc Dipole Magnet
Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses
LHC quench values are lowest

17. 3.Commissioning with beam17

18. Calibration of the particle shower development with beam
Motivation of the test:
Verification of the correlation between quench level and BLM thresholds
Verify „real-life“ quench levels
Verify simulated BLM signal and loss patterns
Provoked magnet quench:
check steady state losses quench limit with circulating beam (part of the MPS commissioning)‏
check fast losses quench behaviour with sector test
=> Accurately known quench levels will increase operational efficiency! 18

19. tests with beam: sector test
see presentations of A. Koschik in CHAMONIX 06 and R. Assman at this workshop
simple idea: steer pilot beam into aperture and check the BLM response to a known lost intensity
slowly increase the intensity up to magnet quench to check the quench level evaluation
List of priorities of the magnets to be revisited in collaboration with MPP: low quench level magnets (MQM,MQT), main magnets (MB, MQ),...

20. tests with beam: circulating beam
check steady state losses quench limit with circulating beam (part of the MPS commissioning)‏
first proposal : R. Assman's presentation on quenches with beam
second proposal : local orbit bump to slowly steer the beam to aperture at a chosen magnet.
possibility to repeat the test with higher beam energy

21. Topology of the losses
Position of the detectors optimized to catch losses from the aperture limitation and middle of the quad
but a change of 25 cm in the impact point position makes a factor 2 in the signal
thresholds at the worst case (conservative) or at the most likely(statistics needed)? 21

22. Trade-Off: Number of Quenches vs. False Aborts
(-) not all quenches caught
(+) no false aborts
(-) all quenches caught
(+) many false aborts
Assumed quench limit
BLM threshold
given by the same simulation toolkit
quench test calibration

23. Changing thresholds The APPLIED threshold table is set to:
30 % of the quench levels for cold elements in the most likely loss topology
relative to the damage level for warm elements: proposal from R. Schmidt for safe beam flag value (conservative)‏
BLM monitor thresholds are trim able individually or by families with a recorded trim history, only possible before filling the machine
For machine protection issues, trim is limited bellow a pre-defined max safe allowed value” of the different equipment (energy and integration dependant), the so-called “MASTER” table
The MASTER table values are set above the quench level (factor 5?) and below the estimated damage levels values
details of the implementation presented at the 86th LTC‏ in January 23

24. Baseline scenario
The MASTER table should only be changed infrequently because this is the reference backed-up table for the BLM system
APPLIED table is set to initial recommended value using pre-defined families
If REALLY needed, APPLIED thresholds can be trimmed up to the MASTER table value‏
All BLM are initially configured as unmaskable, configuring a BLM as maskable should only be done under exceptional circumstances
Any changes can only be done without beam in the machine (removal of the Beam_Permit)‏
Initially, only a group of few experts is allowed to do any change in the MASTER table and to TRIM the APPLIED table. (Two different groups and names can be added)‏
Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses
LHC quench values are lowest 24

25. tests with beam: warm elements
simulations available for some elements, mainly collimators,
but missing info for others: TDI, kickers, warm magnets ...
assumptions/extrapolation are needed to set the thresholds
calibration tests required:
I do not propose to check the damage level!
Calibration of the BLM response to a given number of protons on TDI (see V. Kain's talk)‏
same on TCT (critical element for protection)‏
Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses
LHC quench values are lowest 25

26. possible origins of the losses
distinction between the global (= LHC-wise) loss pattern and the local (= quad-wise) one
some examples:
misalignement => local peak
aperture limitation => local peak
orbit bump => local peak
collimators settings => global loss map
injection losses => next Arc
Beam blow up => global
gas bump => local peak
D3 failure => local peak
...
intensive simulation work done but still needed to complete the catalogue

27. Expected results of the tests
Strategy of threshold settings mainly lead by simulations
All these tests allow to confirm the MODELS used for determining the thresholds
optimised thresholds settings from an experimental point
adjustment of the threshold levels on warm elements to the requested protection level (for example : max number of lost protons/s)‏
Then we can move to the global understanding of the loss patterns 27

28. scenarios given measured beam losses
compare the observed loss patterns with the “catalogue” of typical signatures
keep on furnishing this catalogue, before beam and with beam.
courtesy of F. Follin 28

29. Conclusions
Tests with beam are requested to validate the simulations and further reduce the number of future quenches during operation
The commissioning of the BLMs with beam is well disentangled from collimator settings
The bigger the catalogue of typical loss maps, the faster the understanding of the global loss maps
Flexibility of thresholds adjustment exists to further optimise following operational experience (worst case or most likely)‏