Integrating Radiation Monitoring System for the ATLAS Detector at the Large Hadron Collider

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Integrating Radiation Monitoring System for the
ATLAS Detector at the Large Hadron
Collider Igor Mandic1, Vladimir Cindro1,
Gregor Kramberger1 and Marko Miku1,2 1Joef
Stefan Institute, Ljubljana, Slovenia 2 Faculty
of Mathematics and Physics, University of
Ljubljana, Slovenia
I. Mandic, 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

7 TeV p
7 TeV p
Inner Detector
I. Mandic, 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. Mandic, 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. Mandic, 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. Mandic, 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
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 lt 30 V also after irradiation
• with 1015 n/cm2

Current at 20C before annealing
Depletion voltage before annealing
I. Mandic, 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

?Ib/Ic keq?eq kth ?th

• keq, kth and ?eq known
• gt ?th can be determined

I. Mandic, 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
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• unknown temperature conditions at
• some locations
• could be between -20C and 20C
• stabilize temperature to 20C by heating
• back side of the ceramic hybrid
• thick film resistive layer R 320 O

? T 40C can be maintained with P 2 W.
I. Mandic, 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. Mandic, RADECS 06, Athens, Greece
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• schematic view of readout chain

PP2
ELMB
CAN BUS
PC-PVSSII
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
twisted pairs 1 m
PP1 board
I. Mandic, RADECS 06, Athens, Greece
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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 24C)
  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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• 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 ?eq k?V
• ?V 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. Mandic, RADECS 06, Athens, Greece
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• Diode under reverse bias
• bulk current of fully depleted diode measured
  ?eq ?Ibulk/(a(t,T) V)
• a leakage current damage constant
  (410-17 Acm-1, 1 week at RT after irrad.)
• V sensitive volume of the diode
  (6.2510-4 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 ?eq measured with
  diodes
• ? ?thermal (?Ib/Ic - keq
  ?eq)/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)

I. Mandic, RADECS 06, Athens, Greece
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Annealing of forward Voltage in BPW34
Annealing of leakage current damage factor in
epitaxial diode