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Optical fibre sensors for environmental monitoring at lhc and slhc experiments
Optical fibre sensors for environmental monitoring at LHC and SLHC experiments

N. Beni(ATOMKI / CERN); G. Breglio (Federico II / Optosmart); S. Buontempo (INFN Napoli / CERN); M. Consales (Sannio); A. Cusano(Sannio / Optosmart); A. Cutolo(Sannio / Optosmart); M. Giordano (CNR Napoli / Optosmart); P. Petagna (CERN); Z. Skillasi(ATOMKI / CERN)

  • Fibre Optical Sensors (FOS) applications

  • Fibre Bragg Grating FOS (FBG) specificities

  • First FBG applications in HEP: T and e measurements in CMS

  • New R&D line: FBG as Relative Humidity sensors

  • Polyimide coated FBG as RH sensors: experimental results


Pout=k·RFilm·Pin

  • k is a constant

  • RFilm is the film reflectance

Reflectivity

-B [nm]

ΔRfilm=f (ΔεFilm , ΔdFilm , Δεext)

  • εFilm is the complex dielectric constant of the film

  • dFilm is the film thickness

  • εext is the external medium dielectric constant

  • Concept of Fibre Optical Sensor (FOS)

  • Multipoint distributed sensor through fibre grating

Single-mode optical fiber

External medium

  • Single point sensor through fibre tip coating

Sensitive layer


  • For a large number of environmental monitoring and industrial applications fiber-optic sensor technology now offers several advantages for significant metrological improvement through:

  • Immunity to electromagnetic interference

  • Lightweight

  • Possibility to work in hard environments

  • Intrinsic Radiation Hardness

  • High sensitivity, versatility and bandwidth

  • Simple multiplexing

  • Absence of electronic circuitry in the measurement area

  • This technology is suitable for remote measurements and it is, by definition, compatible with the fiber-optic communication networks


FOS fields of application

Bandgap engineering

Integrationwith:

Photonicdevices

Metal oxide particle layers

Nanoporous Polymers

Carbon nanotubes

Microstructuration

Tapering

Tapered Fiber

Micro-structured Fiber Gratings

Long period Fiber Gratings

Micro resonators

Hollow core optical fiber

Measuredparameters:

Applicationto:

Strain

Temperature

Vibration

Refractiveindex

Chemical detection

Humidity

Electric and Magneticfield

1 

0.1 C°

Up to 1 MHz

10-5

< 1 ppm

< 1%

Structuralhealthmonitoring

Damage detection

Aeronauticmonitoring

Geodetical monitoring

Enviromental monitoring

Acoustic monitoring

Railwaysmonitoring



Cladding

Core

Source LED

Transmittedsignal

Reflected signal

Fibre Bragg Grating FOS

l1,l2,…ln

l2,…ln

l1

L=l1/2neff

  • Where:

  • neffis the effective refractive index of the fibre

  •  is the grating pitch

  • B is the reflected Bragg wavelength

Any strain or temperature perturbationexperiencedby the FBG results in a Braggwavelengthshift



First use of FBG sensors in HEP: CMS

In the last two years the CMS experiment at LHC accepted to pioneer the application of FOS (FBG) to an HEP experiment

  • ~ 100 T or e sensors placed in the following areas in CMS:

    • HF region negative side (Raiser and Castor table)

    • Tracker bulkhead on both sides (10-10 sensor)

    • Experimental Cavern (60) (in January 2011)

(in 2009)

Aim:

  • demonstrate feasibility

  • follow mechanical changes induced by magnetic field (HF-)

  • Monitor the T distribution in front of the Tracker

  • (2011) monitor the cavern environment


e measurement during 2011 magnet ramp-up

Far side

Near side


Z-

Z+

One year record of temperature measured by FBG follows the activity of Tracker and provide information on the thermal mapping of the critical area between the TK and the EE


  • Additional60 FBG T sensors has been installed inthe experimental cavern in January 2011 :

    • 23 sensors on wall near side

    • 3 sensors on ceiling +Z side

    • 23 sensors on wall far side

    • 8 sensors on shaft far side

    • 3 sensors on ceiling -Z side

    • Some HOURS of work to install all of them!

    • In the figures a snapshot of the T distribution on the rack balconies is shown

19.1

19.5

20.0

20.1

19.8

19.5

19.6

19.8

19.2

18.9

19.9

20.3

21.7

19.9

19.1

19.8

20.3

21.8

19.9

19.2

19.2

19.6

20.0

19.8

19.3

19.8

20.0

19.9

19.2

---

18.7

---

19.2

19.2

18.7

19.2

19.2

---

19.2

19.3

19.6

19.6

19.5

Z-

Z+

19.5

19.7

19.4

Z+

Z-


surface

16.4

Shaft FBGs are installed

16.4

16.6

16.9

16.8

17.1

17.5

Daily temperature peak of the top sensor appearing when shaft plug is open (every day a bit later than the previous one): effect of direct sunlight discriminated

Shaft plug closed

18.6

cavern


CURRENTLY AT CERN (typical)

  • HUMIDITY SENSOR SPECIFICATIONS FOR HEP TRACKING DETECTORS

  • Low mass

  • Small dimensions

  • Insensitivity to magnetic field

  • Operation at temperature down to -40 ˚C

  • Response to the full range [0, 100]% RH

  • Reduced number of wires needed

  • Radiation resistance to doses up to 1 MGy

  • HIH 4000 series by Honeywell

  • Small

  • Inexpencive

  • 3 wires for each measuring point

  • Accuracy of 3,5%RH

  • Response time 15s

  • Minimum operation temperature -40°C

  • Notradiationresistant!!!


Motivations for R&D on new RH sensors

  • Almost all miniaturized humidity sensors presently available on the market are electronic sensors (mainly capacitive-based, followed by resistive-based).

  • Despite all efforts, these sensors still fail to provide a complete set of favourable characteristics, e.g., good linearity, high sensitivity, low uncertainty, low hysteresis and rapid response time.

  • For an application in HEP detectors, one should add to this the sensitivity to electro-magnetic noise pick-up, the suitability for multi-point distributed measurements and the resistance to ionizing radiations.

Nowadays – although important requirements on environmental control exist, in particular for Trackers – there is no miniaturized humidity sensor on the market well suited for HEP detector applications


Realizationofhumiditysensorbycoating the gratingswith a suitedpolymer.

Sensingprinciple

Absorbtionofmoistureby the polymericcoating

Bragg wavelength shift

Expansion of the coating (“swelling”)

Strain induced on the FBG

FBG2

RH SENSOR

FBG1

T- SENSOR

Temperature compensation is needed

POLYIMIDE COATING

FBG as relative humidity sensor

  • Bare FBG isinsensitivetohumidity.

  • Useof sensitive material ascoatingof the FBG to induce a mechanicaleffect.

  • Hygroscopicpolymersswelluponadsorptionof water molecules.


Starting point: polyimide coating

2002

2005

  • Relative humidity range limited to 10 – 90 % RH

  • Temperature range limited to 10 ÷ 65 °C

  • Completely unexplored effect of ionizing radiations


RH testing / calibration facility @ CERN

Test section

Insulated confinement

Ranges:

0% ≤ RH ≤ 100%

-20 °C ≤ T ≤ +30 °C

Chilled mirror

Thermally controlled liner

External air circulation

(dry + saturated air mixer)

Closed loop circulation

(salt solution in box)

Salt solution container (if needed)


Optoelectronic interrogation system


Custom fabricated polyimide coated FBG

  • Naked FBG outsourced under strict specifications

  • In-house multiple dip coating + oven curing cycles with PI2525 HD MicrosystemPyralin

Family 1 (thin): coating thickness = 8 mm

Family 2 (thick): coating thickness = 17 mm


Low temperature & humidity properties

Family 2 (thick): coating thickness = 17 mm

(typical)

Family 1 (thin): coating thickness = 8 mm

(typical)

NOTE:

Time response very (too?) slow at T < 0 C

Temperature sensitivity:

Temperature sensitivity:

ST=9.54 pm/°C±0.9%

ST=10.08 pm/°C±12.4%

Humidity sensitivity:

Humidity sensitivity:

SRH=0.42 pm/%RH±7,.%

SRH=2.09 pm/%RH±19.6%


First ionizing irradiation dose: 10 kGy

Perfect l peak invariance after first irradiation

Family 1 (thin): coating thickness = 8 mm

Family 2 (thick): coating thickness = 17 mm

Note: Honeywell HIH 4000 dies (no signal) after 10 kGy ionizing irradiation dose


Further irradiation level: 50 kGy

T = 0 C: before and after irradiation

T = 20 C: before and after irradiation

g-irradiation tests up to 50 kGy* show good radiation resistance and suggest no further variation after the first level (possibility of applying a “pre-stress”)

* latest data at 100 kGy confirm the observation


More technical details and results?

“Relative Humidity Monitoring by Polyimide-Coated Fiber Bragg Grating Sensors for High-Energy Physics Applications”

Accepted to IEEE Sensors 2011 (Limerick-Ireland)


Further developments

  • Continue irradiation studies up to 1 MGy

  • Perform tests at intermediate T (accurate T dependence estimate)

  • Accurate measurement of response time in function of T

  • Develop reliable packaging for field operation

  • Study different kind of polymeric coatings (epoxies?)

  • Feasibility of different gratings for direct humidity reading (LPG)

  • Create a real network among all FOS developments suited for HEP (Full scale cryogenic thermometers, Magnetic field measurement, Dosimeters, CFRP and Silicon –embedded strain measurement,…)

  • Resubmission of the FOS4HEP MC ITN proposal

ONGOING

2012

FUTURE


THANK YOU FOR YOUR ATTENTION!

(RESERVE SLIDES FOLLOW)


RESERVE: e and T discrimination in FBG


RESERVE: e and T discrimination in FBG


RESERVE: e and T discrimination in FBG


RESERVE: e and T discrimination in FBG


RESERVE: e and T discrimination in FBG








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