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Optical links for the CMS Tracker at CERN. J. Troska (on behalf of Karl Gill) CERN EP Division. Outline. 1. Introduction Project LHC/CMS/Tracker/Optical Links Environment 2: Radiation damage testing at CERN Lasers fibres/connectors photodiodes System considerations 3: Summary

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optical links for the cms tracker at cern

Optical links for the CMS Tracker at CERN

J. Troska (on behalf of Karl Gill)

CERN EP Division

outline
Outline
  • 1. Introduction
    • Project
      • LHC/CMS/Tracker/Optical Links
      • Environment
  • 2: Radiation damage testing at CERN
      • Lasers
      • fibres/connectors
      • photodiodes
      • System considerations
  • 3: Summary
  • Copies of slides available: http://gill.home.cern.ch/gill/talks.html
lhc at cern
LHC at CERN

Large Hadron Collider

27 km circumference

7 TeV proton beams

CMS

CERN, Geneva

cms tracker development
CMS Tracker development

Layers of silicon microstrip detectors

Barrel layer prototype

~10 million detector channels

Forward disk prototype

cms tracker analogue optical link
CMS Tracker analogue optical link
  • Transmitter - 1310nm InGaAsP EEL
  • Fibres and connectors - Ge-doped SM fibre
  • Receivers - InGaAs 12-way p-i-n
  • plus analogue electronics - rad-hard deep sub-micron
tracker radiation environment
Tracker radiation environment
  • high collision rate
  • high energy
  • large number of tracks
    • radiation damage
  • lifetime >10 years
  • temperature -10C

Charged hadron fluence (/cm2 over ~10yrs)

cms tracker readout and control links
CMS Tracker readout and control links
  • final system:

Analogue Readout

50000 links @ 40MS/s

Parts under test

for radiation

damage

FED

Detector Hybrid

Tx Hybrid

96

Rx Hybrid

processing

MUX

A

buffering

APV

4

DAQ

2:1

D

amplifiers

12

12

C

pipelines

128:1 MUX

PLL Delay

Timing

DCU

TTCRx

TTC

Digital Control

2000 links @40MHz

FEC

Control

64

4

TTCRx

CCU

CCU

8

processing

buffering

CCU

CCU

Back-End

Front-End

environments
Environments
  • Optoelectronics already employed in variety of harsh radiation environments
    • e.g. civil nuclear and space applications

Total

dose

(Gy)

1E+8

Space (p,e)

Nuclear

(g, also n)

1E+6

CMS TK

1E+4

1E+2

CMS

cavern

1E+0

1E-2

1E-2

1E+0

1E+2

1E+4

1E+6

Dose rate (Gy/hr)

cots issues
COTS issues
  • Extensive use of commercial off-the-shelf components (COTS) in CMS optical links
    • Benefit from latest industrial developments
      • cheaper
      • “reliable” tested devices
    • However COTS not made for CMS environment
      • no guarantees of long-life inside CMS
  • validation testing of COTS mandatory before integration into CMS
cots components for cms tracker links
COTS components for CMS Tracker links
  • Some examples:

96-way cable

1-way InGaAsP edge-emitting lasers

on Si-submount with ceramic lid

12-way optical ribbon

and MT-connector

single fibre

and MU connector

validation procedures for rad resistance
Validation procedures for rad-resistance
  • E.g. lasers and photodiodes

Highlighted:

1999 Market survey

validation tests

(in-system) lab tests

girradiation

pirradiation

ageing

nirradiation

annealing

(in-system) lab tests

  • Feedback test results into system specifications
    • radiation damage effects can then be mitigated
neutron tests at uc louvain la neuve
Neutron tests at UC Louvain-La-Neuve

Recent validation tests

of laser diodes

~20MeV neutrons

flux ~ 5x1010n/cm2/s

fluence ~ 5x1014n/cm2

(Similar to CMS Tracker

10 year exposure)

deuterons

neutrons

Samples stacked

inside cold box (-10C)

neutrons

radiation test system
Radiation test system
  • Test setup for in-situ measurements
  • In-situ measurements give powerful capability to extrapolate damage effects to other radiation environments
    • e.g. CMS Tracker, if damage factors of different particles known
  • Similar test setup for p-i-n and fibre studies
neutron damage italtel nec lasers
neutron damage - Italtel/NEC lasers

Light output vs current characteristics

before and after neutron irradiation

Fluence = 5x1014n/cm2

temperature =23C

Damage effects consistent with build-up of

non-radiative recombination centres in/around

active laser volume, causing a decrease in

injected charge carrier lifetimes

neutron damage italtel nec ld
neutron damage - Italtel/NEC LD

Damage vs fluence and time

Roughly linear

increase in damage

with fluence

annealing vs time

Same annealing dynamics for threshold and efficiency therefore indicate same underlying physical damage mechanism

different vendors compared
Different vendors compared
  • Ithr and Eff changes vs neutron fluence
  • similar effects in all 1310nm InGaAsP lasers
radiation source comparison italtel nec laser
Radiation source comparison - Italtel/NEC laser

For comparison with other sources:

Normalize to fluence = 5x1014p/cm2

in 96 hours irradiation

Extend to 10 years, taking into account LHC luminosity profile

Damage factor ratios:

0.8MeV n = 1

~6MeV n = 3.1

~20MeV n = 4.9

330MeV pi = 11.5

24GeV p = 9.4

possible to estimate damage to laser threshold in CMS Tracker:

in worst case, at low radiiDIthr = 14mA for Italtel/NEC lasers

tests of fibre attenuation
Tests of fibre attenuation
  • Gamma damage (CMS-TK COTS single-mode fibres) at 1310nm
tests of photodiodes leakage
Tests of photodiodes - leakage
  • leakage current (InGaAs, 6MeV neutrons)
  • similar damage over many (similar) devices
photodiodes response
Photodiodes - response
  • Photocurrent (InGaAs, 6MeV neutrons)
  • Significant differences in damage
  • depends mainly if front or back-illuminated
    • front-illuminated better
photodiode single event upset
Photodiode Single-event-upset
  • Bit-error-rate for 80Mbit/s transmission with 59MeV protons in InGaAs p-i-n (D=80mm)
  • 10-90° angle, 1-100mW optical power
  • flux ~106/cm2/s (similar to that inside CMS Tracker)

beam

90°

45°

10°

  • Ionization dominates for angles close to 90°
  • nuclear recoil dominates for smaller angles
  • BER inside CMS Tracker similar to rate due to nuclear recoils
  • should operate at ~100mW opt. power
system considerations
System considerations
  • Build in radiation damage compensation into optical link system
    • Lasers
      • provide adjustable d.c. bias to track threshold increase
      • provide variable gain to compensate for efficiency loss (and other gain factors)
    • Fibres and connectors
      • No significant damage
    • Photodiodes
      • provide leakage current sink
      • provide adjustable gain
      • use sufficient optical power (~100mW) to avoid significant SEU effects
summary
Summary
  • CMS Tracker Optical links project
    • 50000 analogue + 1000 digital links
    • harsh radiation environment, 10 years at -10C
    • COTS components
  • Extensive validation testing of radiation hardness necessary
    • ionization damage (total dose)
    • displacement damage (total fluence) and annealing
    • reliability
    • SEU
  • Accumulated knowledge of radiation damage effects
    • compensation built into optical link system
    • confidence of capacity to operate for 10 years inside CMS Tracker

http://cern.ch/cms-tk-opto/

radiation environment in cms
Radiation environment in CMS
  • **
  • high collision rate
  • high energy
  • large number of tracks
    • radiation damage
  • require lifetime >10 years
  • operating temperature -10C
  • fluences up to 2x1014cm-2
  • (dominated by charged pions)
  • total dose up to 150kGy
slide27

Experimental setup for particle-induced BER

Optical receiver circuit

Optical attenuator

PIN diode

Single-mode optical fiber

1310nm laser transmitter

Optical power-meter

Output signal

Input signal

Bit Error Rate tester

Incident beam

annealing current
Annealing (current)
  • damage anneals faster at higher forward bias
  • “recombination enhanced annealing”
reliability
Reliability
  • irradiated device lifetime > 10 years??
  • Ageing test at 80C
  • No additional degradation in irradiated lasers
  • acc. Factor ~400 relative to -10C operation
  • lifetime >>10years
fibre attenuation vs fluence
Fibre attenuation vs fluence
  • ‘Neutron’ damage (CMS TK)
  • damage actually most likely due to gamma background
damage picture
Damage picture
  • Defects introduced into band-gap by displacement damage
  • non-radiative recombination at defects
    • competes with laser recombination
fibre annealing
Fibre annealing
  • damage recovers after irradiation (e.g. gamma)
  • Damage therefore has dose-rate dependence
ingaas p i n characteristics
InGaAs p-i-n characteristics
  • Output current vs incident power
  • InGaAs p-i-n -5V
  • before/after 2x1014p/cm2
  • Increase in Ileak
  • decrease in Iphoto
different particles leakage
Different particles (leakage)
  • leakage current (InGaAs, different particles, 20C)
  • higher energy p, p more damaging than n
different particles response
Different particles (response)
  • different particles:
  • higher energy p, p more damaging than n
ingaas p i n annealing
InGaAs p-i-n annealing
  • After pion irradiation (room T, -5V)
  • Leakage anneals a little
  • No annealing of response
ingaas p i n reliability
InGaAs p-i-n reliability
  • irradiated device lifetime > 10 years??
  • Ageing test at 80C
  • No additional degradation in irradiated p-i-n’s
  • lifetime >>10years
pd seu
PD SEU
  • photodiodes sensitive to SEU
  • strong dependence upon particle type and angle
lhc radiation environments experiments
LHC Radiation environments: experiments
  • e.g CMS neutrons

(courtesy M. Huhtinen)

lhc radiation environments experiments1
LHC Radiation environments: experiments
  • e.g CMS photons

(courtesy M. Huhtinen)

lhc radiation environments trackers
LHC Radiation environments: Trackers
  • (charged hadrons)

(courtesy M. Huhtinen)

lhc radiation environments trackers1
LHC Radiation environments: Trackers
  • (neutrons)

(courtesy M. Huhtinen)