Commissioning of BLM system

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

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BLM for machine protection

• The only system to protect LHC from fast losses
  (between 0.4 and 10 ms)
• The only system to prevent quench

• Arc Dipole Magnet

• dynamic range 102 -1010 MIPs/(cm2s)

BLM
BLM QPS
damage
BLM
Quench
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BLM system Detector

• about 3600 ionisation chambers 310 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
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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

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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)

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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
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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)
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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

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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)

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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

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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.

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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)

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Proposed implementation
LSA

• Threshold GUI
• Reads the master table
• Applies a factor to a family (lt1)
• 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)
• -gt Details of implementation under discussion

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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?).

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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 32000 values per
  channel for the chosen running sum (need to be
  specified by LBDS)
• Collimation on request, 32 consecutive sums of
  2,54 ms

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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 Flt1, by families

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Other uses of BLM

• Mobile BLM
• 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)

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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

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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-thre
  sholds
• Radiation source check (moving in the tunnel)

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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
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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
• gt 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

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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 -gt Trajectory
• BLM data/logging available
• Up to 6 additional mobile BLMs at the chosen
  locations

Vary intensity5x109 max. 1x1011logging all
relevant data (BPM, BLM,BCT,emittance )
Set optics (3-bump)
Magnet quench
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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)