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© 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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 3
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)
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 4
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 5
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 6
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!
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 7
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 8
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 9
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 10
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 11
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 12
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 13
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)
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 14
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)
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 15
Detection efficiency of fibre optic Cherenkov sensorInfluence of fibre length
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 16
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]
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 17
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 18
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 19
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 20
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 21
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!
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 22
Examples of uses at accelerators: DELTA
Installation at DELTA (Uni Dortmund)
Injection efficiency was poor
DELT
A D
ort
mund
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 23
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 24
Radial arrangement of 4 sensor fibres
Beam pipe
Asymmetric signals can detect directed losses
Fibres
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 25
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 26
Other examples: University Lund and DESY Zeuthen
J. B
ahrd
t, F
EL
20
08
Grabosch, SEI Herbst 2007
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 27
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 28
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 29
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 30
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 31
Fibre optic dosimetryHistorical perspective
S. Kronenberg and C. Siebentritt,Nucl.Instr.Meth. 175 (1980) 109-111
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 32
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 ...“
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 33
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 34
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 35
Power meter system for FLASH
Light source
Power m eter
M ultip lexing unit
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 36
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 37
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 38
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 39
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)
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 40
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 41
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 42
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]
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 43
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 44
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 45
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
© Fraunhofer INT 3rd oPAC Topical Workshop, 2014-05-09, Jochen Kuhnhenn, Slide 46
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