1. Commissioning of BLM system
L. Ponce
With the contribution of B. Dehning, E.B. Holzer, M. Sapinski, C. Zamantzas and all BLM team

2. Outlines Overview of the BLM system Principle of the simulations
Strategy for BLM positioning and the thresholds settings
Signal available
hardware commissioning
commissioning with beam
conclusions

3. BLM for machine protection
The only system to protect LHC from fast losses (between and 10 ms)
The only system to prevent quench
Arc Dipole Magnet
dynamic range : MIPs/(cm2s)
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
BLM
BLM + QPS
damage
BLM
Quench

4. BLM system : Detector
about 3600 ionisation chambers Secondary EMission detectors
measure the secondary shower outside the cryostats created by the losses
dynamic range : 108 (or 1013 with SEM) corresponding to few pA to 25 A
Ionisation chamber:
Diameter = 8.9 cm,
Length 60 cm, 1.5 litre,
Filled with N2
SEM
Diameter = 8.9 cm
Length 15 cm

5. BLM system : signal chain
8 channels per tunnel card, 2 tunnel cards per surface card and 335 surface cards
12 integration periods and 32 energy level per channel (= per monitor)
signal over the thresholds generate a beam dump request via the BIC
Some channels can be maskable with the Safe_Beam flag

6. Simulation : loss locations
Loss pattern given by R. Assmann team (C. Bracco, S. Redaelli, G. Robert-Demolaize) : Example (MQ27.R7)
Peak before MQ at the shrinking vacuum pipe location (aperture limit effect)
End of loss at the centre of the MQ (beam size effect)

7. Simulation : geometry description
GEANT 3 simulation of the secondaries shower created by a lost proton impacting the beam pipe
simulation of the detector response to the spectra registered in the left and right detector (M. Stockner with G4)
500 protons same z position and same energy
Typical impacting angle is 0.25 mrad
longitudinal scan performed for primary impact to optimize the BLM location
Top view

8. Simulation : typical result
Longitudinal distribution of the secondaries outside the cryostat in DS for different loss location (z)
Maximum of the shower ~ 1m after impacting point in material
increase of the signal in magnet free locations
factor 2 between MQ and MB
z (cm)

9. Simulation: Particle Shower in the Cryostat
example of MQ27R7: signal for each location given by the loss map (red) and “sum” signal (black)
Position of the detectors optimized to:
catch the losses:
MB-MQ transition
Middle of MQ
MQ-MB transition
minimize uncertainty of ratio of deposited energy in the coil and in the detector
B1-B2 descrimination

10. Strategy :BLM for quench prevention
beam 1
beam 2
At each Quads, 3 monitors per beam : 2 aperture limitation + middle
positions as much standardized as possible (integration problems) : same procedure for quads in LSS
to define families of monitors (about 250)
Beam dump threshold set to 30 % of the quench level (to be discussed with the uncertainty on quench level knowledge)

12. Strategy: BLM for warm elements
beam 2
top view
collimator
TDI
beam 1
BLM in LSS : at collimators, warm magnets, MSI, MSD, MKD,MKB, all the masks…
Beam dump threshold set to 10 % of equipment damage level (need equipments experts to set the correct values)
Simulation from FLUKA team for IR7 and IR6, from MARS for IR3

13. Generation of threshold table
Quench and damage level threshold tables will be created for each family of BLM locations.
They will be assembled together into MASTER table (damage or quench threshold vs beam energy and integration time)
For every location a threshold for 7 TeV beam will be calculated (seed for parameterization).
Table will be filled from the seed using parameterized dependence of quench level on Energy and Integration time.
MASTER table, MAPPING table (BLM location vs electronic channel) will be stored in LSA database.

14. Calibration and Verification of Models
Simulation is needed for :
secondaries shower simulation
magnet quench (dependance with beam energy, duration, magnet types, 2 dim...)
detector response
Verification :
measurements of the tails of the secondary shower with BLM on HERA dump : comparison with G4 simulation (still to validate, M. Stockner)
quench tests campaign in SM18 for quench magnet model verification (steady state losses) (D. Bocian, A. Siemko)
detector model checked with the CERN/H6 experiment (M. Stockner PhD thesis)

15. Proposed implementation
LSA
Threshold GUI
Reads the “master” table
Applies a factor to a family (<1)
Saves new table to DB
Sends new table to CPU
CPU flashes table if allowed (on- board switch)
Thresholds are loaded from the memory on the FPGA at boot.
Combiner initiated test allows CPU to read ‘current’ table.
Concentrator receives all tables
Compares tables
Notifies BIS (if needed)
-> Details of implementation under discussion

16. Consequences on the reliability of the system?
Flexibility given by changing remotely the thresholds has to be balanced with the loss of reliability of the system
Possibility to scale the thresholds by families (to be discussed which families and who can define it)
The proposed implementation allows both possibilities
But the remote access will have to be validated by machine protection experts when more detailed implementation of MCS and comparator are available (by the beginning of summer?).

17. BLM system : signals available
12 running sums (40 μs to 84 s) to cover the loss duration and 32 energy levels used for filling different buffers:
logging: at 1 Hz, max loss rate in each running sums over the last second + corresponding quench levels + error and status from tests
Post-Mortem + study data : the last 1.7 s with a 40 μs sample rate (43690 values) + the last 2 min of the logging data + thresholds and masking tables + system status info
XPOC : possible to get up to values per channel for the chosen running sum (need to be specified by LBDS)
Collimation: on request, 32 consecutive sums of 2,54 ms

18. Fixed Display in the CCC
Used thresholds values (change with energy)
Loss signals:
Max values of integration intervals between 40 us and 84s updated every 1 s
Values normalised to the used thresholds or in Gy?
BLM concentrated by quad?
If decided, possibility to scale the thresholds table by a factor F<1, by families

19. Other uses of BLM Mobile BLM BLM for ions: Same Ionisation Chambers
use the spare channels per card : 2 in the arcs at each quad, a bit more complicated in the LSS because of more elements.
electronics is commissioned as for connected channel
a separate Fixed display for non-active channels is planned : to be discussed
No dump thresholds
BLM for ions:
same hardware, same electronics, same thresholds as for protons (simulation from R. Bruce)
some more specific loss locations : on dipoles in DS and arcs of IR7 and 3 (G. Bellodi, H. Braun), cells 11 & 13 in IR1 and IR5, cells 10 & 12 in IR 2 (BFPP, J. Jowett and S. Gilardoni)

20. Status of the system
Hardware: IC on time for LHC start-up, SEM delivery in summer
Installation: sector 7-8 done (cables missing in 7 left), sector 4-5 half done (delayed due to LHC schedule), 8-1 started
Acquisition system continuously running at HERA, post-mortem + collimation data check at collimator MD
Threshold comparator software and combiner card (first version done) to be implemented
Fixed display in CCC to be completed by CO
Threshold tables generation : start to specify and implement
post-mortem database and analysis still to be defined
Extensive software tools for data analysis (essential to fulfill the specification). Start now to specify and implement

21. Hardware commissioning
complete detailed procedure documented in MTF
functionalities linked with Machine protection will be reviewed in the Machine Protection System Commissioning Sub-Working Group
validation of the connectivity topology: registration in database of the link between position in the tunnel- channel identification-thresholds
Radiation source check (moving in the tunnel)

22. BLM Testing Procedures
Ph D thesis G.Guaglio
Detector
Tunnel electronics
Surface electronics
Combiner
Functional tests
Barcode check
Current source test (last installation step)
Radioactive source test (before start-up)
HV modulation test (implemented)
Beam inhibit lines tests
Threshold table beam inhibit test (under discussion)
10 pA test
Double optical line comparison (implemented)
Thresholds table and channel assignment SW checks
Inspection frequency:
Reception Installation and yearly maintenance Before (each) fill Parallel with beam

23. Commissioning with beam
see presentation of A. Koschik in CHAMONIX 06
Motivation of the test:
Verification of the correlation between energy deposition in the coil (= quench level) and BLM signal (= thresholds)
Verify or establish „real-life“ quench levels
Verify simulated BLM signal and loss patterns
=> Accurately known quench levels will increase operational efficiency!
simple idea: steer beam into aperture and cause magnet quench
possibility to check steady state losses quench limit with circulating beam (part of the MPS commissioning)
possibility to check fast losses quench behavior if sector test

24. Conditions for a quench test
Requirements :
Pilot beam 5x109
Clean conditions, orbit corrected (to better +/- 3 mm?): need to know impact position and length for determination of the lost proton density
BPM data/logging available -> Trajectory
BLM data/logging available
Up to 6 additional “mobile” BLMs at the chosen locations
Vary intensity 5x109 – max. 1x logging all relevant data (BPM, BLM,BCT,emittance …)
Set optics (3-bump)
Magnet quench

25. Summary
BLM system designed to be reliable and cover the specification of machine protection and quench prevention
Unique hardware and software for all spec to easy maintenance
Controlled, defined test with beam is essential for an early verification of the BLM system, even if beam time consuming
Absolute quench limits and BLM threshold values
Model and understanding of correlation of loss pattern, quench level, BLM signal
Remote access to the thresholds table has still to be approved by machine protection experts
Specification of families to scale has to be defined (OP)