1. Commissioning of BLM system
L. Ponce
With the contribution of C. Zamantzas, B. Dehning, E.B. Holzer, M. Sapiensky

2. Outlines Overview of the system signal available in the CCC
Strategies for the thresholds settings
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
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 system damage protection, no redundancy
Quench protection system (damage protection)

4. Detector
about 3800 ionisation chambers Secondary emission detectors
measure the secondary shower outside the cryostats created by the losses

5. BLMS Signal Chain Multi-plexing and doubling Optical TX Channel 8
Detector
Digitalization
VME Backplane
Optical RX
Superconducting magnet
Secondary particle shower generated by a lost
Demulti-plexing
Signal selec-tion
Thres-holds comp-arison
Channel selection and beam permits gener-ation.
Status monitor
FEE 2
Beam Energy
TUNNEL
SURFACE
FEE 1
Unmaskable beam permits
Maskable beam permits
Front End Electronics (FEE)
Back End Electronics (BEE)

6. Thresholds and interlocks
12 running sums for 32 energy levels for each channel, 16 channels per card, 345 surface cards. → table of 2 millions values!
Any of this signal over the thresholds generate a beam dump request via the BIC

7. 1. Principle of the simulation
Loss pattern given by R. Assmann team (C. Bracco, S. Redaelli, G. Robert-Demolaize)
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
impacting angle is 0.25 mrad
longitudinal scan performed to optimize the BLM location

8. Definition of the thresholds
Loss pattern given by R. Assmann team (C. Bracco, S. Redaelli, G. Robert-Demolaize)
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
impacting angle is 0.25 mrad
longitudinal scan performed to optimize the BLM location

9. Geometry description
3 transverse positions of impact outermost, innermost and top

10. Typical result
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)

11. Particle Shower in the Cryostat
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

12. 2. Position in the ARCS Example of topology of Loss (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)
More simulation are needed to get better evidence (higher populated tertiary halo)

13. Particle shower in the detector
Addition of all the weighted signals from the previous locations
Positions chosen for the arcs also optimum for the DS.

14. BLMs for the arcs beam 1 beam 2
Mainly BLMQI at the Quads (3 monitors per beam) + cold dipoles in LSS
Beam dump threshold set to 30 % of the quench level (to be discussed with the uncertainty on quench level knowledge)
Thresholds derived from loss maps (coll. team), secondaries shower simulations (BLM team), quench level simulations and measurements (D. Bocian)

16. BLMs for warm elements beam 2 beam 1
top view
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

17. Mobile BLM use the spare chambers
use the spare channels per card : 2 in the arcs at each quad, a bit more complicated in the LSS.
electronics is commissioned as for connected channel
a separate Fixed display for non-active channels is planned : to be discussed
detection thresholds: ???

18. 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.
For every location a threshold for 7 TeV will be calculated.
Table will be filled using parametrized dependence on Energy and Integration time.
MASTER table, MAPPING table (BLM location vs electronic channel) will be stored in safe database.

19. Calibration and Verification of Models
Calibration needed for:
verification:
Detector model (Geant) = (CERN /H6)
Detector (particle - energy spectrum dependence)
Magnet model (Geant) = HERA beam dump (tails of shower measurements)
Shower code (prediction error large
for tails)
Threshold table
Magnet quench (2 dim, energy, duration, large variety of magnet types)
Magnet model (SQPL) (heat flow, temp. margin, …) = fast loss: sector test slow loss: SM18

20. Reasons to change the thresholds? How often?
to check Machine Protection functionalities of BLMs (interlocks): decrease the thresholds in order to provoke a dump with low intensity
frequency: during the commissioning, after each shut-down (?), for a set of detectors
study/check of quench levels (“quench and learn” strategy?): implies dedicated MD time, post-mortem data analysis, could be related to check the correct setting of the thresholds
Frequency : ? Probably during shut-down
For HERA, only one change since the start-up

21. some flexibility would help operation but is not an absolute need
commissioning of individual systems (MSI, LBDS, collimators) : to get a loss picture of a region, to give “warning” levels
adjust thresholds after studies of the systems to optimize the operational efficiency vs. the irradiation level
frequency : 1 or 2 iterations after determination of the thresholds and localized in space (injection region, IR7…)
To match quench level during commissioning (operational efficiency):
Probably few iterations
some flexibility would help operation but is not an absolute need

22. Systematic Uncertainties at Quench Levels
about 1 %
Radiation & analog elec.
Electronic calibration
< 10 %
Electronics
sim., measurements with beam (sector test, DESY PhD)
< %
fluence per proton
Simulations
measurements with beam (sector test), Lab meas., sim. fellow)
Source, sim., measurements
Correction means ?
Topology of losses (sim.)
< 200 %
Quench levels (sim.)
< 10 – 20 %
Detector
relative accuracies
Gianluca: radiation SEE
B. Dehning, LHC Radiation Day, 29/11/2005

23. 3. Proposed implementation
Threshold GUI
Reads the “master” table
Applies a factor (<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.
SIS receives all tables
Compares tables
Notifies BIS (if needed)
Note: possible upgrade by adding a comparison with master table on the board BUT feasibility has to be checked

24. 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
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?).

25. System ready for LHC and fulfill the Specifications?
Hardware expected to be ready for LHC start-up
Threshold tables (calibration of BLM) based on simulations.
Analysis effort of BLM logging and post-mortem data (LHC beam data, “parasitic” and dedicated tests) to be started in 2006!
Calibration of threshold tables
Interpretation of BLM signal pattern
 Extensive software tools for data analysis essential to fulfill the specifications! Start now to specify and implement

26. BLMS Testing Procedures PhD 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 (under discussion)
Threshold table beam inhibit test (under discussion)
10 pA test (implemented)
Double optical line comparison (implemented)
Thresholds and channel assignment SW checks (implemented)
Inspection frequency:
Reception Installation and yearly maintenance Before (each) fill Parallel with beam

27. Commissioning Procedures - Steps
Calibration
Functional test
Environmental test
Beam energy
detector
LBDS
BIC
surface elec.
tunnel elec.
magnet
Particle shower
Environmental test: temperature dose & single event
Steps:
Elec. tunnel, 20 year of operation & “no” single event effects
Elec. tunnel, 15 – 50 degree
Functional test: before installation during installation during operation
All equipment, LAB, current and radioactive source
Connectivity, current and radioactive source
Connectivity, thresholds tables
Calibration: before startup after startup
Establishing model (detector, shower, quench behavior)
a: no beam abort , no quench, no action b: use loss measurements and models for improvements

28. Hardware commissioning
complete detailed procedure documented in MTF
functionalities linked with Machine protection will be reviewed in the Machine Protection System Commissioning working Group
validation of the connectivity topology: registration in database of the link position in the tunnel-channel identification-thresholds

29. Commissioning with beam
see presentation of A. Koshick in CHAMONIX
Motivation of the test:
Establish thresholds = establish the correlation between quench level and BLM signal = Calibration!
Verify or establish „real-life“ quench levels
Verify simulated BLM signal (and loss patterns)
In particular: What BLM signal refers to the quench level of a certain magnet type?
=> Accurately known quench levels will increase operational efficiency!

30. How to do the quench test: Implementation
if circulating beam, possibility to check steady state losses quench limit. If sector test, fast losses quench limit
Simple idea: Steer beam into aperture and cause magnet quench
Initial conditions & requirements:
Pilot beam 5x109
Clean conditions, orbit corrected (to better +/- 3 mm?).
BPM data/logging available  Trajectory
BLM data/logging available
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

31. How to do the test: What we want to learn
Beam Parameters
Emittance
Intensity
Momentum spread
Optics Parameters
-function
Dispersion
Trajectory/Orbit
Impact Length
Impact Position
Proton density that caused quench in SC magnet
Determination of quench level
Calibration
BLM signal

32. Conclusions Controlled, defined test to establish
Absolute quench limits
BLM threshold values
Model and understanding of correlation of loss pattern, quench level, BLM signal
This test is essential for an early calibration of the BLM system, even if beam time consuming
It has to be done before increasing intensity