1 Integrating Radiation Monitoring System for the ATLAS Detector at the Large Hadron Collider Igor Mandić 1, Vladimir Cindro 1, Gregor Kramberger 1 and Marko Mikuž 1,2 1 Jožef Stefan Institute, Ljubljana, Slovenia 2 Faculty of Mathematics and Physics, University of Ljubljana, Slovenia I. Mandić, RADECS 06, Athens, Greece

2 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 Inner Detector

3 I. Mandić, RADECS 06, Athens, Greece 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 /cm 2 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

4 I. Mandić, RADECS 06, Athens, Greece 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 n/cm 2  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 ~ n/cm 2  required sensitivity

5  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: Gy to 10 Gy b) 0.25 µm from REM, Oxford, UK range: up to 10 4 Gy c) 0.13 µm from REM, Oxford, UK range: up to10 5 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 , 13-May-05 TID I. Mandić, RADECS 06, Athens, Greece

6 BULK DAMAGE Measurement of forward voltage at 1 mA current in 2 diodes: a) CMRP, University of Wollongong, AU (high sensitivity) range: 10 8 to n/cm 2 (1 MeV NIEL equivalent in Si) b) OSRAM, BPW34 Silicon PIN photodiode, (low sensitivity) range: n/cm 2 to n/cm 2  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 CMRPOSRAM

7 I. Mandić, RADECS 06, Athens, Greece 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 n/cm 2 to n/cm 2  thin epitaxial diode can be depleted with V bias < 30 V also after irradiation with n/cm 2 Current at 20°C before annealing Depletion voltage before annealing

8 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 k eq, k th and Ф eq known => Ф th can be determined ΔI b /I c = k eq ·Ф eq + k th ·Ф th I. Mandić, RADECS 06, Athens, Greece

9 SENSOR BOARD CMRP diode BPW34 diode Thermistor Pad diode Radfet package: 0.25 µm SiO µmSiO µmSiO 2 Bipolar transistors Ceramic hybrid (Al 2 O 3 ) 4 cm

10 I. Mandić, RADECS 06, Athens, Greece 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.

11 I. Mandić, RADECS 06, Athens, Greece 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 (I max = 20 mA,U max = 30 V)

12 I. Mandić, RADECS 06, Athens, Greece USA15 CAN BUS 4 ELMBs connected to one CAN branch PC-PVSSII DAC power supply Type II cable ~ 15 m FCI connector twisted pairs ~ 1 m PP2 Radiation Monitor Sensor Board RMSB ELMB PP2 board DAC PP1 board schematic view of readout chain

13 I. Mandić, RADECS 06, Athens, Greece TEST RESULTS Irradiation with 22 Na 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 22 Na source for ~80 hours  sensitivity better than 1.5 mGy LAAS 1.6 µm radfet

14 I. Mandić, RADECS 06, Athens, Greece Diodes under forward bias 1 MeV equivalent neutron fluence: Ф eq = 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)

15 I. Mandić, RADECS 06, Athens, Greece Diode under reverse bias bulk current of fully depleted diode measured : Ф eq = ΔI bulk /(α(t,T) ·V) α: leakage current damage constant (~4· Acm -1, ~1 week at RT after irrad.) V: sensitive volume of the diode (6.25·10 -4 cm 3 )  large range of fluences can be measured: to n/cm 2 P = 25 W

16 I. Mandić, RADECS 06, Athens, Greece DMILL bipolar transistor base current I b at collector current I c = 10 µA measured 1 MeV equivalent fluence Ф eq measured with diodes  Ф thermal = (ΔI b /I c - k eq · Ф eq )/k th P = 25 W - data from three irradiation sessions - corrected for annealing between sessions

17 I. Mandić, RADECS 06, Athens, Greece Summary system for online radiation monitoring in ATLAS Inner Detector:  total ionization dose in Si0 2,  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)

18 Annealing of forward Voltage in BPW34 Annealing of leakage current damage factor in epitaxial diode