Transcript RadMonTalk

Integrating Radiation Monitoring System for the ATLAS Detector at
the Large Hadron Collider
Igor Mandić1, Vladimir Cindro1, Gregor Kramberger1 and Marko Mikuž1,2
1Jožef
Stefan Institute, Ljubljana, Slovenia
2 Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
I. Mandić, RADECS 06, Athens, Greece
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ATLAS
• experimental apparatus for studying proton-proton collisions at energy
of 7 TeV/proton at the Large Hadron Collider at CERN
• because of high energy and high interaction rate (collisions every 25 ns)
particle detectors and readout electronics close to the interaction
point will be exposed to high levels of radiation
Inner Detector
I. Mandić, RADECS 06, Athens, Greece
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Radiation levels in the Inner Detector
• detectors and electronics will be exposed to radiation arising from primary
vertex (mostly pions) and to neutrons arising from interactions of hadrons
with detector material
• in 10 years of operation parts of inner detector will be exposed to ionization
dose of more than 100 kGy and to fluence of hadrons causing bulk damage in
silicon equivalent to more than 1015 /cm2 of 1 MeV neutrons
• fluence of thermal neutrons of same magnitude as the fluence of fast neutrons
radiation damage will degrade performance of detectors and readout
electronics
monitoring of radiation levels needed to understand detector performance
cross check of simulations of radiation levels to correctly predict damage
I. Mandić, RADECS 06, Athens, Greece
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Radiation Monitor for the Inner Detector
 online radiation monitoring system
 measure ionization dose and bulk damage at 14 locations in the inner detector
 range up to 100 kGy and 1015 n/cm2
 sufficient sensitivity for initial low luminosity years of LHC operation (~ 1.4 % of
planned integrated luminosity per low-luminosity year)
 during low luminosity years at least exposed monitoring location in the ID
doses per day will be ~ 1 Gy and ~ 1010 n/cm2  required sensitivity
I. Mandić, RADECS 06, Athens, Greece
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TID
 Measure gate voltage increase at given drain current in radiation sensitive
p-MOS FET transistors (RadFETs)
Three RadFETs with different gate oxide thicknesses to cover large range of
doses:
a) 1.6 µm from CNRS LAAS, Toulouse, France
range: 0.001 Gy to 10 Gy
b) 0.25 µm from REM, Oxford, UK
range: up to 104 Gy
c) 0.13 µm from REM, Oxford, UK
range: up to105 Gy
Sensor selection, calibration, annealing studies packaging, bonding...
done by: TS-LEA and PH-DT2 groups at CERN
More info in:
F. Ravotti, M. Glaser and M. Moll, “Sensor Catalogue” CERN TS-Note-2005-002, 13-May-05
I. Mandić, RADECS 06, Athens, Greece
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BULK DAMAGE
Two methods: - increase of voltage at given current in forward biased pin diodes
- increase of leakage current in reverse biased pin diode
• Measurement of forward voltage at 1 mA current in 2 diodes:
a) CMRP, University of Wollongong, AU (high sensitivity)
range: 108 to 1012 n/cm2 (1 MeV NIEL equivalent in Si)
b) OSRAM, BPW34 Silicon PIN photodiode, (low sensitivity)
range: 1012 n/cm2 to 1015 n/cm2
CMRP
I. Mandić, RADECS 06, Athens, Greece
OSRAM
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• Measurement of bulk current increase in reverse biased diode
- 25 µm x 0.5 cm x 0.5 cm pad diode with guard ring structure processed
on epitaxial silicon
- suitable for fluences from 1011 n/cm2 to 1015 n/cm2
 thin epitaxial diode can be depleted with Vbias < 30 V also after irradiation
with 1015 n/cm2
Current at 20°C before annealing
Depletion voltage before annealing
I. Mandić, RADECS 06, Athens, Greece
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THERMAL NEUTRONS
• DMILL bipolar transistors used in readout electronics in parts of ID
• measure base current at given collector current in DMILL bipolar transistors
 sensitive to both fast and thermal neutrons
ΔIb/Ic = keq·Фeq + kth ·Фth
• keq, kth and Фeq known
=> Фth can be determined
I. Mandić, RADECS 06, Athens, Greece
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SENSOR BOARD
Radfet package:
• 0.25 µm SiO2
• 1.6 µmSiO2
• 0.13 µmSiO2
CMRP diode
BPW34 diode
Thermistor
Bipolar transistors
Pad diode
Ceramic hybrid
(Al2O3)
4 cm
I. Mandić, RADECS 06, Athens, Greece
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• unknown temperature conditions at
some locations:
could be between -20°C and +20°C
• stabilize temperature to ~20°C by heating
back side of the ceramic hybrid
• thick film resistive layer R = 320 Ω
Δ T = 40°C can be maintained with P = 2 W.
I. Mandić, RADECS 06, Athens, Greece
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READOUT
 use standard ATLAS Detector Control System components
• ELMB: 64 ADC channels, can bus communication
• ELMB-DAC: current source, 16 channels (Imax = 20 mA,Umax = 30 V)
 Readout principles
• RadFETs,PIN: current pulse (DAC)-voltage measured (ADC)
• Pad diode: current (DAC) converted to voltage (resistor) –
voltage on resistor due to leakage current measured (ADC)
• Bipolar transistor: collector current enforced (DAC) –
voltage on resistor due to base current measured (ADC)
 control of back-of-the-hybrid heater: 4 DAC channels
Sensors biased only during readout (e.g. few times every hour)
I. Mandić, RADECS 06, Athens, Greece
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PC-PVSSII
• schematic view of readout chain
ELMB
PP2
CAN BUS
4 ELMBs
connected to one
CAN branch
DAC power supply
USA15
DAC
PP2
board
Radiation Monitor
Sensor Board
RMSB
Type II cable
~ 15 m
FCI
connector
PP1
board
twisted pairs
~1m
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TEST RESULTS
Irradiation with 22Na source
• readout sensors every 10 minutes (sensor contacts shorted during irradiation)
• correct for temperature variation (19 to 24°C) offline (dV/dT = -3.6 mV/K)
• expose to 22Na source for ~80 hours
 sensitivity better than 1.5 mGy
LAAS 1.6 µm radfet
I. Mandić, RADECS 06, Athens, Greece
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Irradiation in the core of the TRIGA reactor in Ljubljana
• neutron flux proportional to reactor power (tunable)
Diodes under forward bias
• 1 MeV equivalent neutron fluence: Фeq = k·ΔV
ΔV: increase of forward voltage at 1 mA forward current
k: calibration constant
P = 25 W
P = 25 W
- data from three irradiation sessions
- corrected for annealing between sessions
I. Mandić, RADECS 06, Athens, Greece
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Diode under reverse bias
• bulk current of fully depleted diode measured : Фeq = ΔIbulk/(α(t,T) ·V)
α: leakage current damage constant (~4·10-17 Acm-1, ~1 week at RT after irrad.)
V: sensitive volume of the diode (6.25·10-4 cm3)
 large range of fluences can be measured: 1011 to 1015 n/cm2
P = 25 W
I. Mandić, RADECS 06, Athens, Greece
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DMILL bipolar transistor
• base current Ib at collector current Ic = 10 µA measured
• 1 MeV equivalent fluence Фeq measured with diodes
 Фthermal = (ΔIb/Ic - keq· Фeq)/kth
P = 25 W
- data from three irradiation sessions
- corrected for annealing between sessions
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Summary
• system for online radiation monitoring in ATLAS Inner Detector:
 total ionization dose in Si02,
 bulk damage in silicon in terms of 1 MeV equivalent neutron fluence,
 fluence of thermal neutrons
 readout compatible with ATLAS Detector Control System
 sufficient sensitivity for low luminosity years of ATLAS
• locations outside of the Inner Detector (lower doses):
 use simpler system with one LAAS radfet and CMRP diode per location
• to improve accuracy:
 irradiations in mixed field environment at low dose rates
 annealing studies
 help of TS-LEA and PH-DT2 groups at CERN,
see contributions by F. Ravotti et al., (papers PH-2, PH-3)
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Annealing of forward
Voltage in BPW34
Annealing of leakage current
damage factor in epitaxial diode
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