1 integrating radiation monitoring system for the atlas detector at the large hadron collider igor...
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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, Slovenia2 Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
I. Mandić, RADECS 06, Athens, Greece
2I. Mandić, RADECS 06, Athens, Greece
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
7 TeV p
7 TeV p
Inner Detector
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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
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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
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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
TID
I. Mandić, RADECS 06, Athens, Greece
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BULK DAMAGE
• 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
Two methods: - increase of voltage at given current in forward biased pin diodes - increase of leakage current in reverse biased pin diode
I. Mandić, RADECS 06, Athens, Greece
CMRP 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
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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
• keq, kth and Фeq known => Фth can be determined
ΔIb/Ic = keq·Фeq + kth ·Фth
I. Mandić, RADECS 06, Athens, Greece
9I. Mandić, RADECS 06, Athens, Greece
SENSOR BOARD
CMRP diode
BPW34 diode
Thermistor
Pad diode
Radfet package: • 0.25 µm SiO2
• 1.6 µmSiO2
• 0.13 µmSiO2
Bipolar transistors
Ceramic hybrid (Al2O3)
4 cm
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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.
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READOUT
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)
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)
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CAN BUS
4 ELMBs connected to one CAN branch
PC-P
VSS
II
DAC power supply
Type II cable ~ 15 m FCI
connector
twisted pairs~ 1 m
PP2
Radiation MonitorSensor Board
RMSB
ELMB
PP2board
DAC
PP1board
• schematic view of readout chain
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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
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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
- data from three irradiation sessions- corrected for annealing between sessions
P = 25 W
Irradiation in the core of the TRIGA reactor in Ljubljana
• neutron flux proportional to reactor power (tunable)
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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
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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 currentdamage factor in epitaxial diode