very high radiation detector for the lhc bl m system based on s econdary e lectron emission
DESCRIPTION
Very High Radiation Detector for the LHC BL M System based on S econdary E lectron Emission. Daniel Kramer , Eva Barbara Holzer, Bernd Dehning, Gianfranco Ferioli CERN AB-BI. LHC Beam Loss Monitoring system. ~ 3700 BLMI chambers installed along LHC - PowerPoint PPT PresentationTRANSCRIPT
2.11.20072.11.2007 IEEE NSS 2007 D.KramerIEEE NSS 2007 D.Kramer 11
Very High Radiation Detector for the LHC BLM System based onSecondary Electron Emission
Daniel KramerDaniel Kramer, Eva Barbara Holzer, Bernd Dehning, , Eva Barbara Holzer, Bernd Dehning, Gianfranco FerioliGianfranco Ferioli
CERN AB-BICERN AB-BI
2.11.20072.11.2007 IEEE NSS 2007 D.KramerIEEE NSS 2007 D.Kramer 22
LHC Beam Loss Monitoring LHC Beam Loss Monitoring systemsystem
~ 3700 ~ 3700 BLMIBLMI chambers chambers installed along LHCinstalled along LHC
~ ~ 280 280 SEMSEM chambers chambers required for high radiation required for high radiation areas:areas:
– CollimationCollimation
– Injection pointsInjection points
– IPsIPs
– Beam DumpsBeam Dumps
– Aperture limitsAperture limits
Main SEM requirementsMain SEM requirements
– 20 years lifetime (up to 20 years lifetime (up to 70MGray/year70MGray/year))
– Sensitivity ~Sensitivity ~3E43E4 lower than lower than BLMIBLMI
2.11.20072.11.2007 IEEE NSS 2007 D.KramerIEEE NSS 2007 D.Kramer 33
LHC Beam Loss Monitoring LHC Beam Loss Monitoring systemsystem
~ 3700 ~ 3700 BLMIBLMI chambers chambers installed along LHCinstalled along LHC
~ ~ 280 280 SEMSEM chambers chambers required for high radiation required for high radiation areas:areas:
– CollimationCollimation
– Injection pointsInjection points
– IPsIPs
– Beam DumpsBeam Dumps
– Aperture limitsAperture limits
Main SEM requirementsMain SEM requirements
– 20 years lifetime (up to 20 years lifetime (up to 70MGray/year70MGray/year))
– Sensitivity ~Sensitivity ~3E43E4 lower than lower than BLMIBLMI
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Secondary Emission Monitor Secondary Emission Monitor working principleworking principle
Secondary electronsBias E fieldTi Signal electrodeTi HV electrodes
Steel vessel (mass)
Secondary Electron Emission is a surface phenomenon
Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy
SE are pulled away by HV bias field (1.5kV)
Signal created by e- drifting between the electrodes
Delta electrons do not contribute to signal due to symmetry*
< 10-4 mbar
VHV necessary to keep ionization inside the detector negligible
Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)
No direct contact between Signal and Bias (guard ring)No direct contact between Signal and Bias (guard ring)
2.11.20072.11.2007 IEEE NSS 2007 D.KramerIEEE NSS 2007 D.Kramer 55
Secondary Emission Monitor Secondary Emission Monitor working principleworking principle
Secondary electronsBias E fieldTi Signal electrodeTi HV electrodes
Steel vessel (mass)
Secondary Electron Emission is a surface phenomenon
Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy
SE are pulled away by HV bias field (1.5kV)
Signal created by e- drifting between the electrodes
Delta electrons do not contribute to signal due to symmetry*
< 10-4 mbar
Incoming
particle
VHV necessary to keep ionization inside the detector negligible
Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)
No direct contact between Signal and Bias (guard ring)No direct contact between Signal and Bias (guard ring)
2.11.20072.11.2007 IEEE NSS 2007 D.KramerIEEE NSS 2007 D.Kramer 66
Secondary Emission Monitor Secondary Emission Monitor working principleworking principle
Secondary electronsBias E fieldTi Signal electrodeTi HV electrodes
Steel vessel (mass)
Secondary Electron Emission is a surface phenomenon
Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy
SE are pulled away by HV bias field (1.5kV)
Signal created by e- drifting between the electrodes
Delta electrons do not contribute to signal due to symmetry*
< 10-4 mbar
Incoming
particle
VHV necessary to keep ionization inside the detector negligible
Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)
No direct contact between Signal and Bias (guard ring)No direct contact between Signal and Bias (guard ring)
2.11.20072.11.2007 IEEE NSS 2007 D.KramerIEEE NSS 2007 D.Kramer 77
Secondary Emission Monitor Secondary Emission Monitor working principleworking principle
Secondary electronsBias E fieldTi Signal electrodeTi HV electrodes
Steel vessel (mass)
Secondary Electron Emission is a surface phenomenon
Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy
SE are pulled away by HV bias field (1.5kV)
Signal created by e- drifting between the electrodes
Delta electrons do not contribute to signal due to symmetry*
< 10-4 mbar
Incoming
particle
VHV necessary to keep ionization inside the detector negligible
Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)
No direct contact between Signal and Bias (guard ring)No direct contact between Signal and Bias (guard ring)
2.11.20072.11.2007 IEEE NSS 2007 D.KramerIEEE NSS 2007 D.Kramer 88
Secondary Emission Monitor Secondary Emission Monitor working principleworking principle
Secondary electronsBias E fieldTi Signal electrodeTi HV electrodes
Steel vessel (mass)
Secondary Electron Emission is a surface phenomenon
Energy of SE (below ~ 50 eV, dominant for signal) is independent on primary energy
SE are pulled away by HV bias field (1.5kV)
Signal created by e- drifting between the electrodes
Delta electrons do not contribute to signal due to symmetry*
< 10-4 mbar
Incoming
particle
VHV necessary to keep ionization inside the detector negligible
Very careful insulation and shielding of signal path to eliminate ionization in air (otherwise nonlinear response)
No direct contact between Signal and Bias (guard ring)No direct contact between Signal and Bias (guard ring)
Incoming
particle
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SEM production assemblySEM production assembly All components chosen
according to UHV standards
Steel parts vacuum fired
Detector contains 170 cm2 of NEG St707 to keep the vacuum < 10-4 mbar during 20 years
Pinch off after 350°C vacuum bakeout and NEG activation (p<10-
10mbar)
Ti electrodes partially activated (slow pumping observed)
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Simulations in Geant4 Simulations in Geant4
Detailed Geometry of SEM F type implemented Detailed Geometry of SEM F type implemented
– Signal electrode covered by thin layer of TiOSignal electrode covered by thin layer of TiO2 2
PPhoto-hoto-AAbsorption-bsorption-IIonization module used for onization module used for production of delta electronsproduction of delta electrons
QGSP_BERT_HP used as main physics listQGSP_BERT_HP used as main physics list
Signal generation done bySignal generation done by
– calculating calculating charge balancecharge balance on signal electrode on signal electrode
– recording “recording “True SETrue SE” produced by custom generator” produced by custom generator
Production threshold for eProduction threshold for e++/e/e-- set to 9 set to 9mm
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Semi empirical approach using Semi empirical approach using simplified Sternglass formulasimplified Sternglass formula
Secondary Emission Yield is Secondary Emission Yield is proportional to electronic proportional to electronic dE/dx in the surface layerdE/dx in the surface layer
– LLSS = (0.23 N = (0.23 Ngg))-1-1
gg = 1.6 Z = 1.6 Z1/31/31010-16-16cmcm22
““TrueSEY” of each particle TrueSEY” of each particle crossing the surface boundary crossing the surface boundary calculated and SE recorded calculated and SE recorded with this probabilitywith this probability
Correction for impact angle Correction for impact angle included in simulationincluded in simulation
Fast Fast electrons considered as electrons considered as other primariesother primaries
Model calibration factor
Penetration distance of SE
Electronic energy loss
Comparison => CF = 0.8
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Simulated response curves for Simulated response curves for different particle typesdifferent particle types
Geant4 version Geant4 version 8.1.p018.1.p01
30k primaries 30k primaries for each for each energy pointenergy point
Longitudinal Longitudinal impactimpact
Gaussian Gaussian beam beam
rr = 2mm = 2mm
e- absorbed in electrode
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Longitudinal Longitudinal impact of proton impact of proton beambeam
rr = 2mm = 2mm
Chamber tilted Chamber tilted by ~1by ~1°°
Simulation sensitive Simulation sensitive to beam angle and to beam angle and divergencedivergence
Negative signal due Negative signal due to low energy e- to low energy e- from secondary from secondary shower shower
400 GeV Beam scan in TT20 SPS 400 GeV Beam scan in TT20 SPS lineline
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Longitudinal Longitudinal impact of proton impact of proton beambeam
rr = 2mm = 2mm
Chamber tilted Chamber tilted by ~1by ~1°°
Simulation sensitive Simulation sensitive to beam angle and to beam angle and divergencedivergence
Negative signal due Negative signal due to low energy e- to low energy e- from secondary from secondary shower shower
400 GeV Beam scan in TT20 SPS 400 GeV Beam scan in TT20 SPS lineline
chamber diameter
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Prototype tests with 63MeV Prototype tests with 63MeV cyclotron beam in Paul Scherer cyclotron beam in Paul Scherer InstituteInstitute
Prototype C -> more Prototype C -> more ceramics inside (no guard ceramics inside (no guard ring) ring)
Prototype F -> close to Prototype F -> close to production versionproduction version
Current measured with Current measured with electrometer Keithley 6517Aelectrometer Keithley 6517A
HV power supply FUG HLC14HV power supply FUG HLC14
Pattern not yet fully Pattern not yet fully understoodunderstood
– Not reproduced by Not reproduced by simulationsimulation
High SE response if High SE response if U_bias > 2VU_bias > 2V
Geant4.9.0 simulated SEY = Geant4.9.0 simulated SEY = 25.525.50.8%0.8%
PSI proton beam 62.9MeV BLMS prototypes F & C Type HV dependence of SEY
10-3
10-2
10-1
100
0.2
0.25
0.3
0.35
0.4
HV [kV]
De
tect
or
resp
on
se [c
ha
rge
s/p+
]
C typeF typeGeant4
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Measurements in PS Booster Measurements in PS Booster Dump line with 1.4 GeV proton Dump line with 1.4 GeV proton bunchesbunches Older prototype used - Older prototype used -
Type CType C
Profiles integrated with Profiles integrated with digital oscilloscopedigital oscilloscope
– 1.5kV bias voltage1.5kV bias voltage
– 80m cable length80m cable length
– 50 50 termination termination
– Single bunch passageSingle bunch passage
SEY measurementSEY measurement
– 4.9 4.9 0.2% 0.2%
Geant4.9.0 simulationGeant4.9.0 simulation
– 4.2 4.2 0.5% 0.5%
Normalized response
0 0.5 1 1.5 2 2.5
x 1012
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Beam intensity [p+/bunch]
Det
ecto
r re
spon
se [c
harg
es/p
+]
DataGeant4.9fit Data
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BLMS compared to BLMS compared to reference radiation reference radiation monitor ACEM monitor ACEM (Aluminum Cathode (Aluminum Cathode Electron Multiplier Electron Multiplier tube)tube)
ACEM not directly in ACEM not directly in the beamthe beam
Rise/fall time < 50 nsRise/fall time < 50 ns
– Dominated by Dominated by unknown intensity unknown intensity distributiondistribution
Normalized intensity Normalized intensity 1.3 101.3 101919pp++/s/s
SEM response to single proton bunch of SEM response to single proton bunch of 2.16 102.16 101313 protons with 160ns length protons with 160ns length
Measurements in PS Booster Measurements in PS Booster Dump line with 1.4 GeV proton Dump line with 1.4 GeV proton bunchesbunches
-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-20
0
20
40
60
80
100
120
140
160
Cur
rent
SE
M [m
A]
time [s]-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
1
2
3
4
5
Cur
rent
AC
EM
[mA
]
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ConclusionsConclusions The BLMS detector was successfully tested in The BLMS detector was successfully tested in
different proton beamsdifferent proton beams
Geant4 simulations are in good agreement with Geant4 simulations are in good agreement with these experimentsthese experiments
– => chosen model is validated=> chosen model is validated
Sign change of output current possible Sign change of output current possible under very specific circumstancesunder very specific circumstances
Verification measurements in mixed radiation Verification measurements in mixed radiation field of LHC test collimation area in SPS are field of LHC test collimation area in SPS are ongoingongoing
360 BLMS Detectors were produced in IHEP 360 BLMS Detectors were produced in IHEP Protvino and will be tested soonProtvino and will be tested soon