Beam Loss Monitoring System of the LHC
Eva Barbara Holzer, CERN
for the LHC BLM team
IEEE Nuclear Science Symposium
October 26, 2005
Fajardo, Puerto Rico
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
1
Beam Loss Monitoring System of the LHC




Specification and Requirements
Architecture of the BLM System
Threshold Calibration
Summary
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
2
Stored Beam Energies
(Based on graph from R. Schmidt)
Energy stored in the beam [MJ]
1000.00
LHC top
energy
100.00
LHC injection
(12 SPS batches)
10.00
Factor
~200
ISR
SPS fixed
target
1.00
HERA
TEVATRON
SPS batch to
LHC
0.10
LEP2
SNS
SPS
ppbar
RHIC
proton
0.01
1
10
100
1000
10000
Momentum [GeV/c]
Quench Levels
Units
Tevatron
RHIC
HERA
LHC
Instant loss (0.01 - 10 ms)
[J/cm3]
4.5 10-03
1.8 10-02
2.1 10-03 - 6.6 10-03
8.7 10-04
Steady loss (> 100 s)
[W/cm3]
7.5 10-02
7.5 10-02
IEEE NSS, Puerto Rico
Eva Barbara Holzer
5.3 10-03
October 26, 2005
3
Large Hadron Collider (LHC)
 In LHC there are:
 514 main quadrupoles
 1232 main dipoles
 ~130 collimators and
absorbers
 pp and PbPb
 Commissioning 2007
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
4
The BLM System: Purpose
 Detection of dangerous beam losses 
generation of trigger for beam extraction
Tevatron Collimator damage, 5.12.2003 (D. Still)
 Setup of the collimators and continuously
monitor their performance
 Localization of beam losses and
identification of loss mechanism
 Machine setup and studies
LHC Collimator prototype
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
5
The BLM System: Challenges
 Reliable (tolerable failure rate 10-7 per hour per channel)
 Reliable components, radiation tolerant electronics
 Redundancy, voting
 Monitoring of availability and drift of channels
 Less than 2 false dumps per month (operation efficiency)
 High dynamic range (108, 1013 – two monitor types at the same
location)
 Fast (1 turn, 89 s) trigger generation for dump signal
 Quench level determination with an uncertainty of a factor 2
(calibration)
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
6
Locations
 6 detectors around each quadrupole (~3000)
 Maskable: Beam abort signal can be ignored, when the stored energy in
the beam is below the damage limit
 Critical aperture limits or critical loss positions (~400)
 Non-maskable
 Collimators and absorbers (~150)
 Non-maskable
 Plus a set of movable BLMs
 All non-maskable monitors have to be available before injection
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
7
Quench and Damage Levels
Arc Dipole Magnet
Dynamic
Range
Arc: 108
Collimator: 1013
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
8
Signals from the BLM system
 Dump signal to the LHC beam interlock system (LBIS), 2 types
(maskable and non-maskable)
 Post mortem
 Up to 1000 turns plus averages of 10 minutes
 Data for the control room and logging (1Hz)
“Artist’s View” of the Beam Loss Display (C. Zamantzas)
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
9
Beam Loss Monitoring System of the LHC




Specification and Requirements
Architecture of the BLM System
Threshold Calibration
Summary
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
10
Monitor Types
 Design criteria: Signal speed and robustness
 Dynamic range (> 109) limited by leakage current
through insulator ceramics (lower) and saturation due to
space charge (upper limit).
Secondary Emission Monitor
(SEM):
 Length 10 cm
 P < 10-7 bar
 ~ 30000 times smaller
gain
Ionization chamber:
 N2 gas filling at 100 mbar overpressure
 Length 50 cm
 Sensitive volume 1.5 l
 Ion collection time 85 s
 Both monitors:
 Parallel electrodes (Al, SEM: Ti)
separated by 0.5 cm
 Low pass filter at the HV input
 Voltage 1.5 kV
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
11
System Layout
LBIS
Threshold Comparator: Losses integrated and compared to threshold
table (12 time intervals and 32 energy ranges).
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
12
Beam Loss Monitoring System of the LHC




Specification and Requirements
Architecture of the BLM System
Threshold Calibration
Summary
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
13
Threshold Determination
 Beam dump threshold set to 30% of the magnet quench level
 Specification:
Absolute precision
(calibration)
factor 2 (final)
factor 5 (initial)
Relative precision for
quench prevention
< 25%
 Calibration of Thresholds:
 Based on simulations
 Cross-checked by measurements when possible
 Beam tests might be necessary to reach the required precision
 Aim of calibration  relate the BLM signal to the:
 Number of locally lost beam particles
 Deposited energy in the machine component
 Quench and damage levels
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
14
Threshold Determination
Injection Optics, 450 GeV, Horizontal Halo
Warm Magnet
Cold Magnet
Collimator
 Proton loss locations (MAD-X,
SIXTRACK, BeamLossPattern,
measurements: LHC beam)
 Hadronic showers through magnets
(GEANT, measurements:
HERA/DESY, LHC beam)
 Magnet quench levels as function of
proton energy and loss duration
(SPQR, measurements: Laboratory,
LHC beam)
 Chamber response to the mixed
radiation field in the tail of the hadronic
shower (GEANT, GARFIELD,
measurements: booster, SPS, H6,
HERA/DESY)
(S. Redaelli, L. Ponce)
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
15
Threshold Determination
 Proton loss locations (MAD-X,
SIXTRACK, BeamLossPattern,
measurements: LHC beam)
 Hadronic showers through magnets
(GEANT, measurements:
HERA/DESY, LHC beam)
 Magnet quench levels as function of
proton energy and loss duration
(SPQR, measurements: Laboratory,
LHC beam)
 Chamber response to the mixed
radiation field in the tail of the hadronic
shower (GEANT, GARFIELD,
measurements: booster, SPS, H6,
HERA/DESY)
(E. Gschwendtner)
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
16
Threshold Determination
 Proton loss locations (MAD-X,
SIXTRACK, BeamLossPattern,
measurements: LHC beam)
 Hadronic showers through magnets
Conductors
(GEANT, measurements:
3
HERA/DESY, LHC beam)
Vacuum
tube
 Magnet quench levels as function of
proton energy and loss duration
First layer Second layer
(SPQR, measurements: Laboratory,
LHC beam)
metal
Helium
Helium
helium
 Chamber response to the mixed
insulation
radiation field in the tail of the hadronic
-channels
heat source shower (GEANT, GARFIELD,
measurements: booster, SPS, H6,
Cryogenic
HERA/DESY)
Spacers
System
Outer layer
Inner layer
(D. Bocian)
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
17
Threshold Determination
 Proton loss locations (MAD-X,
SIXTRACK, BeamLossPattern,
measurements: LHC beam)
 Hadronic showers through magnets
(GEANT, measurements:
HERA/DESY, LHC beam)
 Magnet quench levels as function of
proton energy and loss duration
(SPQR, measurements: Laboratory,
LHC beam)
 Chamber response to the mixed
radiation field in the tail of the hadronic
shower (GEANT, GARFIELD,
measurements: booster, SPS, H6,
HERA/DESY)
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
18
Beam Loss Monitoring System of the LHC




Specification and Requirements
Architecture of the BLM System
Threshold Calibration
Summary
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
19
Summary – Features of the BLM System
 Large dynamic range
 High reliability and low false beam abort rate (radiation tolerant
electronics, fail safe design)
 Extensive simulations for threshold calibration
 Dynamically changing threshold values
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
20
The LHC BLM Team
Bernd Dehning, Ewald Effinger, Jonathan Emery, Gianfranco Ferioli,
Jose Luis Gonzalez, Edda Gschwendtner, Gianluca Guaglio, Michael
Hodgson, Eva Barbara Holzer, Daniel Kramer, Roman Leitner, Laurette
Ponce, Virginia Prieto, Markus Stockner, Christos Zamantzas
Contributions from members of the:
 LHC Machine Protection Working Group (http://cern.ch/lhc-mpwg)
 LHC Collimation Working Group (http://cern.ch/lhc-collimation)
IEEE NSS, Puerto Rico
Eva Barbara Holzer
October 26, 2005
21