© fraunhofer int fibre optic sensors at accelerators – considerations and pitfalls jochen...

© Fraunhofer INT

Fibre Optic Sensors at Accelerators – Considerations and Pitfalls

Jochen Kuhnhenn

10-1 100 101 102 103 104

100

101

102

103

104

Ind

uce

d L

oss

[d

B/k

m]

Dose [Gy]

GI F-doped (?) GI P-doped GI Ge-doped SI Pure silica

© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 2

Fibre Optic Sensors at AcceleratorsOverview

Radiation effects in optical fibres

Radiation detection with optical fibres Fibre-optic beam-loss monitors Fibre-optic integrating dosimeters

Fibre optic temperature and strain sensors at accelerators


Introduction of radiation effects group at Fraunhofer INTBackground of experience

Investigation of radiation effects in electronic and opto-electronic components since 25 years

Operating several dedicated irradiation facilities(Co-60, Neutrons, X-Ray, …)

Supports manufacturers and users (space, accelerators, medicine, nuclear facilities, …)

Specialised knowledge led to the development of several unique radiation detection systems

Fraunhofer Locations in Germany

Thanks to our collaborators: DESY (M. Körfer, K.

Wittenburg) HMI (F. Wulf, W. Goettmann) BESSY (J. Bahrdt) CERN (T. Wijnands, D. Ricci,

Elisa Guillermain)


12

3

Radiation effects in optical fibresOverview

Throughout this presentation “Radiation” means ionising radiation(X-rays, g-rays, particles)

Radiation changes all properties of optical fibres, but some are only relevant at high doses with small (practical) influence Change of refractive index Change of bandwidth Change of mechanical properties (e.g. dimension, strength)

Radiation-induced luminescence light Most important effect in this context Cherenkov radiation

Most obvious and disturbing effect is an increase of their attenuation (RIA) Strongly depending on actual fibre and radiation environment


Parameter dependencies of RIAExperimentally observed effects

Manufacturing influences Fibre type (Single mode,

graded index, step index) Doping of core/

Doping of cladding(for SM fibres)

Preform manufacturer and used processes

Core material manufacturer OH Content Cladding core diameter ratio

(CCDR) Coating material Drawing conditions

Operation conditions Wavelength Light power Launch conditions

Environment Total dose Dose rate Annealing periods / Duty

cycle Temperature

In combination with each other: Differences of many orders ofMagnitude possible!


Wavelength dependenceExample of Ge-doped GI fibre

800 1000 1200 1400 1600

10

100

1000

Indu

ced

Loss

[dB

/km

]

Wavelength [nm]

AT&T MM 3AD=1000 Gy


Example of dependenciesCore doping effects (~830 nm)

What does that mean for injected light of 1 mW: Wavelength: ~830 nm Fibre length: 100 m

Pure silica fibre: 0.89 mW F-doped fibre: 0.17 mW Ge-doped fibre: 310-6 mW P-doped fibre: 10-200 mW

10-1 100 101 102 103 104

100

101

102

103

104

Ind

uce

d L

oss

[d

B/k

m]

Dose [Gy]

GI F-doped (?) GI P-doped GI Ge-doped SI Pure silica


Differences between manufacturersGI fibres and SI fibres

10-1 100 101 102 103 104

100

101

102

103

Commercial Fiber 1 Commercial Fiber 2 Commercial Fiber 3 Commercial Fiber 4

Indu

ced

Loss

[dB

/km

]

Dose [Gy]

50/125 µm GI-Fibers = 830 - 865 nmD = 2.9 - 13.9 Gy/min

Ge-doped core

(Ge+

P)-dop

ed c

ore

100 101 102 103 1041

10

100

Oxford Electronics Ltd.(Acrylate Coating)

Ind

uce

d Lo

ss [d

B/k

m]

Dose [Gy]

Heraeus-Tenevo (CCDR 1.2)

j-plasma (CCDR 1.1)

Oxford Electronics Ltd.(Polyimide Coating)

=854 nm, T=23°C


Radiation effects in optical fibres: Short summary

Huge (orders of magnitude) differences between different fibres, environments and operation conditions

Reliable and application specific radiation testing requires experience

Difficult to transfer or even compare results of different tests

No predictive theoretical model available, some extrapolations possible

There are only very few “rules of thumb” you can trust!

Carefully review sales information, question simplified statements


Main advantages of optical fibres as radiation sensorsGeneral and for accelerator applications

Immune against external electro-magnetic-fields

Do not disturb external high precision magnetic fields, e.g. in the undulator section of free electron lasers

Environmental conditions (temperature, vacuum, …) usually no major problem

Capable of monitoring extended areas

Extremely small sensors: diameter of much less than 1 mm


Introduction to light guiding in step-index optical fibres

Total reflection of light if angle below critical value

Different possible light paths cause dispersion

Parameters of interest: Difference of refractive index between core and cladding Launch conditions into fibre (angle of incident)


Wavelength dependencies for Cherenkov detection Light guiding and

signal detection dependent on the following contributions Fibre attenuation

as a function of wavelength

Photon efficiency of selected photodetector

Wavelengths of interest: 400 nm to 800

nm 200 300 400 500 600 700 800 900

10-1

100

101

Gen

erat

ed C

here

nkov

-Pho

tons

per

Ele

ctro

nIn

trin

sic

Fib

re A

tten

uatio

n [d

B/1

0 m

]R

elat

ive

PM

T E

ffic

ienc

y (m

ultip

lied

by 1

0)

Wavelength [nm]

Cherenkov-Photons per Electron Fibre Attenuation [dB/10 m] Relative PMT Efficiency (x 10)


Detection efficiency of fibre optic Cherenkov sensorInfluence of fibre length


Detected signals as a function of fibre length

Decrease of signal due to (intrinsic) attenuation in the fibre

Comparable signals at different locations if events are within ~20 m

BUT: No influence of radiation-induced attenuation considered

1 10 1000

10

20

30

40

50

60

Det

ecte

d P

hoto

ns [

a.u.

]

Fibre Length [m]


Photon collection efficiency

Full light cone has to be taken into account Possibility for grazing incident and spiral light propagation

G.

An

zivin

o e

t. a

l.,

NIM

A(3

57

)38

0


Lots of 3-D simulation results

Meas.

Sci

. Te

chnol. 1

8 (

20

07

) 3

25

7–3

26

2

Vol. 45, No. 36 APPLIED OPTICS 9151

NIM

A 3

57

(1

99

5)

38

0

P. G

oro

detz

ky e

t. a

l.,

NIM

A(3

61

)16

1

Rad

iat.

Phys.

Chem

. V

ol.

41

, p

p.

25

3,

19

93

CERN-ATS-2011-066


Experimental angular dependence

NIM

A 3

57

(1

99

5)

36

9N

IM A

35

7 (

19

95

) 3

80

NIM

A 3

60

(1

99

5)

23

7D

OI:

10

.10

63

/1.1

57

09

4590°

NIM

A 3

67

(1

99

5)

27

1


Installation at accelerators

Version 2: PMT looks downstream

Beam pipe Beam

PMT

Beam pipe Beam

PMT

Version 1: PMT looks upstream

Advantages: Higher signal due to better geometry

Advantages: Better resolution (“velocity” for time scaling: 0.4 c) Always correct order of events recorded in PMT


Selection of a Cherenkov fibreGeneral considerations

Manufacturer: Really know who has drawn the fibre, who has made the preform

Selecting the fibre type: Established recommendation:

High OH pure-silica core step-index fibre with F-doped silica cladding

Alternatives might become more interesting soon (see below) Selecting the core diameter:

The larger the core, usually the higher the price Minor dependence of bandwidth and core diameter (if any)

Selecting the NA: Compromise between efficiency and bandwidth: Dt ≈

L/(2nc)*(NA)² Shield ambient light with buffer, e.g. black nylon

Perform dedicated, meaningful radiation tests!


Examples of uses at accelerators: DELTA

Installation at DELTA (Uni Dortmund)

Injection efficiency was poor

DELT

A D

ort

mund


Examples of results at DELTA: Injection efficiency

-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Before After

Cer

enko

v S

igna

l [V

]

Position (relative to Trigger) [m]

Kuhnhenn, d

oi: 1

0.1

11

7/1

2.6

24

03

9


Radial arrangement of 4 sensor fibres

Beam pipe

Asymmetric signals can detect directed losses

Fibres


Results of the Cherenkov system at FLASH undulators

500 520 540 560 580-1.0

-0.5

0.0

0.5

1.0

X

Y

BPM

Undulator Section

Tran

sver

se L

oss

Trac

eTime [ns]

X Loss Trace Y Loss Trace

Beam

1 2

34

Wire Scanner BPM BPM Wire Scanner BPM

500 520 540 560 580

0

200

400

600

800

BPM

Undulator Section

PM

T V

olta

ge [m

V]

Time [ns]

PMT Channel 1 PMT Channel 2 PMT Channel 3 PMT Channel 4

Beam

1 2

34

Wire Scanner BPM BPM Wire Scanner BPM

F. Wulf, 2009 IEEE Nuclear Science Symposium


Other examples: University Lund and DESY Zeuthen

J. B

ahrd

t, F

EL

20

08

Grabosch, SEI Herbst 2007


Advantages of fibre optic Cherenkov detectors

“Real time” commissioning and optimisation

Prevents damages due to high undetected beam losses

Simple to install and covers whole accelerator areas

Proven and used routinely at several installations


Considerations for fibre optic Cherenkov detectorsSelection between “equal” pure-silica core fibres At 850 nm At 660 nm

1 10 100 1000 10000

1

10

100

Ind

uzie

rte

Däm

pfun

g [d

B/k

m]

Dosis [Gy]

FC1.2PIL FC1.2ACL FC1.2ACS FC1.1PIL FC1.1ACL FC1.1ACL FC1.1ACS HT1.1ACL (2) HT1.1ACS (Fehl) HT1.1ACS (2,v2) HT1.2ACL (2,v2) HT1.2ACS (2) OxfordPolyimid OxfordAcrylat

0.1 1 10 100 1000 100001

10

100

1000

Indu

zier

te D

ämpf

ung

[dB

/km

]

Dosis [Gy]

FC1.1PIL (660) B FC1.2PIL (660) A FC1.2ACL (660) A FC1.2ACS (660) A FC1.1PIL (660) A FC1.1ACL (660) A FC1.1ACS (660) A HT1.2PIL2 (660) A HT1.2ACL2 (660) A HT1.2ACS2 (660) A HT1.1PIL2 (660) A HT1.1ACL2 (660) A HT1.1ACS2 (660) A CO Sample 1 (660) A CO Sample 2 (660) A CO Sample 3 (660) A CO Sample 4 (660) A CO Sample 5 (660) A


Considerations for fibre optic Cherenkov detectorsNew optical fibres with better (UV) radiation resistance Solarisiation-optimised

optimised fibres F-doped core optical fibres

DO

I: 1

0.1

10

9/T

NS

.20

10

.20

42

61

5

A. A

less

i, p

rese

nte

d a

t R

AD

EC

S 2

01

1

365 nm 214 nm310 nm551 nm


Fibre optic dosimetryHistorical perspective

S. Kronenberg and C. Siebentritt,Nucl.Instr.Meth. 175 (1980) 109-111


Fibre optic dosimetryA long way from the idea to the real application

Gaebler, 1983:„... fibres exhibit properties, which are excellent suited for their application as radiation detectors.“

Lyons, 1985:„... P-doped fibers ... might be ... suitable for ... dosimetry.“

Henschel, 1992:„... radiation induced loss ... has been investigated with respect to the suitablility for radiation dosimetry purposes.“

Borgermans, 1999:„The ... fibre may be used for dosimetry applications ...“

West, 2001:„ response of P-doped fibres is reviewed ... [for] their possible use in dosimetry.“

van Uffelen, 2002:„Feasibility study for distributed dose monitoring ...“


Fibre optic dosimetryPrinciple: Measuring RIA in P-doped optical fibres

0 1000 2000 3000 4000 5000 6000

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Induce

d L

oss

[dB

/m]

Time [s]

Irradiation Annealing

(Ge+P)-doped

Ge-doped

Properties of radiation induced attenuation (RIA) in P-co-doped optical fibres: Strong effect

High sensitivity Linear dose response

Quantitative results Slow annealing

Dose rate independence High reproducibility

Only one calibration per fibre sample necessary


Fibre optic dosimetryCalibration and dose rate dependency

One fit covers all dose rates(>4 orders of magnitude difference)

Nearly lineardose-attenuation function

Saturation of induced attenuation only above ~1000 Gy

Calibration for this fibre: D[Gy] A[dB/m] * 27 10-4 10-3 10-2 10-1 100 101 102 103 104

10-5

10-4

10-3

10-2

10-1

100

101

102

l=678 nm

Induce

d L

oss

[dB

/m]

Dose [Gy(SiO2)]

Fit 0.00618 Gy/min 0.0624 Gy/min 2.175 Gy/min 9.606 Gy/min 69.342 Gy/min

A [dB/m] = 0.0369 × (D [Gy])0.972


Power meter system for FLASH

Light source

Power m eter

M ultip lexing unit


Exemplary results for power meter measurements at TTF1

2002-03-25 2002-04-01 2002-04-08 2002-04-15 2002-04-22 2002-04-29

0

50

100

150

200

250

300

350

400

Akkumulierte Dosis (Neue Anordnung)seit 2002-03-21

UND 1.1 UND 1.2 UND 1.3 UND 1.4 UND 1.5 UND 1.6 UND 1.7 UND 1.8 UND 1.9 UND 2.1 UND 2.2 UND 2.3

Dos

is [G

y]

Datum

Ostern

Dose

[G

y]

Date

Accumulated dose since 2002-03-21 compared to TLD measurements

Easter


Power meter system at MAXlab, Sweden: Results

2007-04-01 2007-06-01 2007-08-01 2007-10-01 2007-12-01 2008-02-01 2008-04-01 2008-06-01

0

20

40

60

80

100

120

140

160

180 Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 Channel 6 Channel 7 Channel 8 Channel 9 Channel 10 Channel 11 Channel 12 Channel 13 Channel 14 Channel 15 Channel 16

Do

se

[G

y]

Date

2007-12-12 2007-12-13 2007-12-14 2007-12-15 2007-12-16 2007-12-17

0

10

20

30

40

50

60

70

80 Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 Channel 6 Channel 7 Channel 8 Channel 9 Channel 10 Channel 11 Channel 12 Channel 13 Channel 14 Channel 15 Channel 16

Dos

e [G

y]

Date


Power meter system at MAXlab, Sweden: Results

080411 1100 080411 1200 080411 1300 080411 1400 080411 1500 080411 1600

0

5

10

15

20

25

30

35

Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 Channel 6 Channel 7 Channel 8 Channel 9 Channel 10 Channel 11 Channel 12 Channel 13 Channel 14 Channel 15 Channel 16

Dos

e [G

y]

Date


Fibre optic dosimeters based on RIA measurements

Simple principle requires sophisticated measurement techniques for reliable and accurate data

Main advantages: Integrating (even if no readout takes place) Small sensor size (< 0.5 mm if necessary) Quantitative dose data

(tested for different dose rates and radiation energies) High sensitivity (~ some 10 mGy/hour)


Using Fibre-Bragg-Gratings in radiation environmentsPrinciple

Applications for FBGs: Temperature

sensors Strain

sensors „Mirrors“ for

fibre lasers

Advantages: Distributed

system Passive

l = 2 n L

Light source Transmittedspectrum

Reflectedspectrum gChange of refractive

index due to radiation


Radiation effects in Fibre-Bragg-GratingsDifferences in manufacturing method and used fibre

0 20 40 60 80 1001

10

100

1000

10000

B [p

m]

Dose [kGy]

CLPG; ~5000 pmVery sensitive radiation sensor

UV FBG; 100 pmHigh dose radiation sensor

Fs-IR FBG; 5 pmRadiation „hard“ temperatureand strain sensor

Dl B

[p

m]

Dosis [kGy]


Using other fibre optic sensors in radiation environments

The above mentioned advantages of fibre optic sensors are attractive for other measurements at accelerators

Widely used fibre optic sensors in conventional environments Strain (bridges, buildings, tunnels, …) Temperature (tunnels, dams, …) Moisture (tunnels, dams, …)

Application in radiation environments can be challenging


Example: Fibre optic temperature sensor

Principle: Similar to OTDR measurement but not the original backscattered

signal is analysed but two spectrally shifted peaks (stokes and anti-stokes)

Temperature information is derived by comparing the amplitudes of the two signals

Problem in radiation environment: Radiation induced loss strongly depends on wavelength

One peak (at lower wavelength) gets more attenuated than the other on (at higher wavelength)

Radiation leads to apparent temperature change


Last slide

Overview of radiation effects in optical fibres was given This presentation introduced different radiation sensors using optical

fibres Cherenkov systems Power meter systems Fibre-Bragg-Gratings

Finally some other aspects of using optical fibres at accelerators were presented, such as using optical fibre sensors in radiation environments

Unfortunately not covered Telecommunication applications in radiation environments (e.g.

CERN) Stimulated annealing of radiation induced attenuation


Thank you for your attention!

Contact: Jochen Kuhnhenn

Fraunhofer INTAppelsgarten 253879 Euskirchen

Email: [email protected] Tel.: +49-2251-18 200

Fax: +49-2251-18 38 200

© fraunhofer int fibre optic sensors at accelerators – considerations and pitfalls jochen...

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