1 Integrating Radiation Monitoring System for the ATLAS Detector at the Large Hadron Collider Igor Mandić 1, Vladimir Cindro 1, Gregor Kramberger 1 and

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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


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


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


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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


CMRP OSRAM


• 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



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


• 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.


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)


USA15

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


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


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)


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


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


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

Documents

1 Integrating Radiation Monitoring System for the ATLAS Detector at the Large Hadron Collider Igor Mandić 1, Vladimir Cindro 1, Gregor Kramberger 1 and