BEAM LOSS MONITORING SYSTEM

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BEAM LOSS MONITORING SYSTEM

• B. Dehning, E. Effinger, G. Ferioli, J.L.
  Gonzalez, G. Guaglio,
• M. Hodgson, E.B. Holzer, L. Ponce, V. Prieto, C.
  Zamantzas
• CERN AB/BDI
• External Review of LHC Collimation Project
• July 1, 2004

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Outline

• BLM System
• Hardware
• Dynamic Range
• Positioning of Monitors
• Signals from the BLM system
• Simulations of Cleaning Insertions
• Momentum Cleaning (Igor A. Kurochkin, IHEP)
• Betatron Cleaning (M. Brugger, S. Roesler, CERN
  SC/RP)
• Summary

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THE BLM SYSTEM

• Purpose
• Machine protection against damage of equipment
  and magnet quench
• Setup of the collimators
• Localization of beam losses and identification of
  loss mechanism
• Machine setup and studies
• Challenges
• Reliable (tolerable failure rate 10-7 per hour
  per channel)
• High dynamic range (108, 1013)
• Fast (1 turn trigger generation for dump signal)

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Families of BLMs
Type Area of use Time resolution Number of monitors
BLMC Collimation sections 1 turn 100
BLMS BLMS Critical aperture limits or critical positions 1 turn(89 us) 500
BLMA All along the rings (ARC, ) 2.5 ms 3000
BLMB Primary collimators 1 turn bunch-by-bunch 10

• BLMC BLMS In case of a non working monitor
  this monitor has to be repaired before the next
  injection

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Loss Detectors Ionization Chamber
SPS Chamber Gas N2, Volume 1 Liter, 30 Al
disks of 0.5 mm, Typical bias voltage 1500 V.
New LHC chamber design Diameter 8.9 cm, Length
60 cm, 1.5 litre, Filled with Ar or N2
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Secondary Emission Monitor
Diameter 8.9 cm Length 15 cm
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Dynamic Range (I)
Secondary Emission Monitor P lt 10-7 bar
Ionization Chamber P gt 1bar
Efficiency SE 0.05
charges/particle
Efficiency ioniz. Chamber 50 charges /
(particle cm)
Efficiency Ionization Chamber / Efficiency SE
3 104
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Dynamic Range (II)
Beam Loss Current BLMC and BLMS
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System Layout
Threshold Comparator Losses integrated in 12
time intervals to approximate quench level curve.
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Quench and Damage Levels

• Detection of shower particles outside the
  cryostat or near the collimators to determine the
  coil temperature increase due to particle losses

Quench level and observation range 450 GeV 7 TeV
BLMS BLMC
Damage levels
Dynamic Arc 108 Collimator 1013
Special Collimator1 turn
Arc 2.5 ms
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Loss Levels and Required Accuracy
Relative loss levels Relative loss levels Relative loss levels
450 GeV 7 TeV
Damage to components 320/5 short/long 1000/25 short/long
Quench level 1 1
Beam dump threshold for quench prevention 0.3 0.3/0.4 short/long
Warning 0.1 0.1/0.25 short/long
Specification
Absolute precision (calibration) lt factor 2 initially lt factor 5
Relative precision for quench prevention lt 25
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Monitor Positions in Arc
Installation of BLMAs on a SSS quadrupole
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Monitor Positions in Collimation
Collimator interconnect with ion pump and BLM
(possible positions)
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Signals from the BLM system

• Dump signal to beam interlock controller (BIC), 2
  types
• Not mask able BLMC and BLMS, 600 monitors.
• Can be masked when safe beam flag is set BLMA,
  3000 monitors
• Post mortem
• 2000 turns plus integral of 10 ms.
• Logging
• Once a second
• Stored in database
• Used for graphical representation in the control
  room
• Values measured for each detector and time
  interval are normalized by their corresponding
  threshold values.

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Artist View of the Logging Display
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Momentum Cleaning
Igor A. Kurochkin
IR3 (6.2) length and positions of collimators
have changed
BLM position
TCS 6,5,4
TCS3,2
TCP1
TCS1

• Activation will reduce the sensitivity of the
  monitors in the low signal range. Expected
  activation 10-2 to 10-4 of mean loss rate (SPS
  10-3)
• Monitors close to vacuum chamber to reduce cross
  talk and background.
• Monitors 30 cm downstream of collimator

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Relative contribution to BLM signal from primary
inelastic interactions in the collimators
Igor A. Kurochkin

• Good signal (from upstream collimator)
• BLM1 100
• BLM2 4
• BLM3 57.4
• BLM4 9
• BLM5 5
• BLM6 4
• BLM7 1
• TCP1 - major contributor to background
• BLM2 96
• BLM7 20

• BLM signal
• Good measure for heat load in the corresponding
  collimator
• Does not represent the number of proton inelastic
  interactions of the corresponding collimator

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Transversal Variation of Monitor Location
Igor A. Kurochkin
Igor A. Kurochkin
TCS1
Total energy deposition. The contribution from
beam 2 (crosstalk) is small (lt1) due to
longitudinal distance.

• Best signal to background and signal to cross
  talk at position near to the beam

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Betatron Cleaning
M. Brugger, S. Roesler

• Primary interactions
• Inelastic interaction rate (star), threshold
  20MeV

• Comparison of energy deposition GeV to
  inelastic interaction rate in IP3
• They scale for the downstream secondary
  collimators (2 3 GeV per inelastic interaction)
• Primary collimator 0.4 GeV
• First secondary collimator 3.3 GeV

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Contribution to the number of inelastic
interactions from beam particle losses in
upstream collimators
M. Brugger, S. Roesler

• Values similar to momentum cleaning.
• Higher inter beam crosstalk can be expected due
  to reduced longitudinal distance between
  collimators of beam 1 and 2.

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Summary

• BLM system machine protection
• First priority (downtime)
• Detectors next to possible loss locations protect
  local equipment
• Monitors in collimation region
• Measure energy deposition in the collimators
• Can not measure primary inelastic interactions
  (response matrix)
• High activation (reduce sensitivity)
• Possible noise problems to be investigated
  (analogue signal cables of BLMs are up to 300 m
  long and close to numerous stepping motor control
  cables)

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Ionization Chamber Currents (1 liter)
450 GeV, quench levels (min) 100 s 12.5 nA
7 TeV, quench levels (min) 100 s 2 nA
Required 25 rel. accuracy, error small against 25 gt 5 100 pA
450 GeV, dynamic range min. 10 10 pA
100 2.5 pA
7 TeV, dynamic range min. 10 s 160 pA
100s 80 pA
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Estimation of fluency through the BLMs
MIN MAX
Total fluency Total fluency Total fluency Total fluency Total fluency
BLMA BLMS 7 TeV 5 103 8 108 MIPs / (cm2 s)
450 GeV 102 1010 MIPs / (cm2 s)
BLMC BLMS 7 TeV 1.5 104 6.4 1013 MIPs / (cm2 s)
450 GeV 2 105 1016 MIPs / (cm2 s)
Fluency through the monitor per lost beam proton Fluency through the monitor per lost beam proton Fluency through the monitor per lost beam proton Fluency through the monitor per lost beam proton Fluency through the monitor per lost beam proton
BLMA BLMS 7 TeV 5 10-3 4 10-2 MIPs / (p cm2)
450 GeV 5 10-4 3 10-3 MIPs / (p cm2)
BLMC BLMS 7 TeV 4 10-1 MIPs / (p cm2)
450 GeV 4 10-2 MIPs / (p cm2)