Draka Comteq
Silica Expertise Group
Attenuation increase
Marcoussis
prediction
in CERN conditions
December 6th, 05
for DRAKA fibers
Silica Expertise Group
RIA prediction, ER| 1
Context
Draka Comteq
Silica Expertise Group
Purpose:
Predict Radiation Induced Attenuation (RIA) at low dose-rate, over a large
period (CERN conditions), based on RIA-measurements performed at higher
dose-rates (Fraunhofer Institute).
Problem:
•
RIA is not linear with dose / exposure time.
•
high dose-rates measurements cannot be directly extrapolated to low dose-rates
 The understanding of RIA phenomena is very important
RIA prediction, ER| 2
Kinetic model
Draka Comteq
Silica Expertise Group
Kinetic modelling of radiation induced attenuation (RIA)
•
Time dependence for defect generation without annealing:
 solution:
.
n1  a1 D t
or
n1  a1D
dn1
 a1 D
dt
D:
. total dose
D: dose-rate
a1: probability of defect generation
Non-reversible mechanism
•
Time dependence for defect generation with finite lifetime:
dn2
n2

 a2 D 
dt
2
.
D: dose-rate, n2: defect concentration, 2: lifetime, a2: probability of defect generation
 solution of saturating exponential type:
.
t
n2 (t )  a2 D 2 [1  exp(  )]
Reversible mechanism
RIA prediction, ER| 3
2
Kinetic model
Draka Comteq
Silica Expertise Group
Non-reversible mechanism
10
.
n2  a2 D t
200
180
160
140
9
8
7
Increasing
dose-rate
120
100
RIA (dB/km)
RIA (dB/km)
Reversible mechanism
80
4
3
40
2
20
1
0
0
200
400
600
800
1000
1
5
60
0
Increasing
.
t
dose-rate n1  a1 D  1[1  exp(  )]
6
0
200
Time (h)
400
600
800
1000
Time (h)
Depends only on total dose
(or dose-rate x irr. time)
Depends on both total dose AND on dose-rate
 becomes negligible for very low dose-rates
Total RIA = sum of both components
RIA prediction, ER| 4
Kinetic model
Draka Comteq
Silica Expertise Group
200
200
Reversible part
Reversible part
Non-reversible part
160
Non-reversible part
160
Total
RIA (dB/km)
RIA (dB/km)
Total
120
80
120
Intermediate dose-rate
80
High dose-rate
40
40
0
0
0
1000
2000
3000
4000
5000
0
1000
Time (h)
2000
3000
Time (h)
In order to predict RIA, it is essential to well-determine both:
- the non-reversible component
- the dose-rate dependency of the reversible component
RIA prediction, ER| 5
4000
5000
Draka model
Draka Comteq
Silica Expertise Group
General
•
Our prediction is based on kinetic model
• reversible component (dose-rate dependent)
Mainly determined from Fraunhofer Institute’s measurements at 4 different dose-rates
• non-reversible component
Determined from both:
- annealing curves measured at Fraunhofer Institue and
- spectral attenuation measurements after total annealing
•
Our prediction is valid for
• l = 1310nm
• for DRAKA SMF and Sample 4
RIA prediction, ER| 6
Draka model
Draka Comteq
Silica Expertise Group
Model for RIA prediction
CERN conditions: Dose-rate = 0.002 Gy/s, Time = 1 year (~ 3.107 s)
Reversible part
.
 irradiation time >> 2
.
RIAsaturation  a2 D  2  C2 D
 Only the saturation level is important
100
Not a linear
behavior
Saturation level (dB/km)
90
80
.
0.44
70
60
Draka 445755
Sat = 42.31x
2
R = 0.99
RIAsaturation  C2 Dg
50
40
30
20
Sat = 23.10x
2
R = 0.99
Sample #4
10
0.36
g = 0.44 for Draka SMF
g = 0.36 for Sample 4
0
0
0.5
1
1.5
2
Dose-rate (Gy/s)
2.5
3
RIA prediction, ER| 7
3.5
Draka model
Draka Comteq
Silica Expertise Group
Model for RIA prediction
CERN conditions: Dose-rate = 0.002 Gy/s, Time = 1 year (~ 3.107 s)
Non-reversible part
40
Non-reversible RIA (dB/km)
.
CEA measurements for CERN (LHC project note 351)
Maximum values
values
Minimum values
Maximum
Minimum values
RIAnonrev  a1 D t  C1 D
Puissance (Minimum values)
Puissance (Maximum values)
Puissance
30
y = 0.005x0.76
R2 = 1.00
y = 0.005x0.78
R2 = 0.99
20
RIAnonrev  C1 D b
+ see also
[Kyoto – 1992]
10
y = 0.006x0.68
R2 = 0.97
0.68 < b < 0.78 for Draka SMF
0.47 < b < 0.52 for Sample 4
0
0
20000
40000
60000
Total dose (Gy)
80000
RIA prediction, ER| 8
100000
[Kyoto – 1992]: JLT Vol. 10, 3, pp289-294
Draka model
Draka Comteq
Silica Expertise Group
RIA prediction for Draka SMF (Sample #445755)
RIA prediction, ER| 9
CEA tests were performed at RT, power ~ 0.5mW,
dose-rate = 0.28 mGy/s, fiber length ~ 5km
Draka model
Draka Comteq
Silica Expertise Group
RIA prediction for Sample 4
RIA prediction, ER| 10
CEA tests were performed at RT, power ~ 0.5mW,
dose-rate = 0.28 mGy/s, fiber length ~ 3km
Comparison Draka / Fraunhofer Institute predictions
Draka Comteq
Silica Expertise Group
Prediction for CERN conditions (mean dose-rate = 0.002 Gy/s)
Draka’s prediction
FI’s prediction
RIA(Draka SMF)> 12 dB/km for
doses > 16 000 to 33 000 Gy
=> The fiber has to be changed
every 1 or 2 years.
Draka’s prediction
RIA(Sample 4)> 12 dB/km for
doses > 100 000 Gy at least
FI’s prediction
=> The fiber does not need to be
changed for 4 to 8 years.
RIA prediction, ER| 11
Comparison Draka / Fraunhofer Institute predictions
Draka Comteq
Silica Expertise Group
Rough extrapolation based on RIA curves shifting (FI extrapolation)
 Parallel RIA curves (in log scale) mean that the difference between curves
obtained at different dose-rates increases with increasing doses.
RIA prediction, ER| 12
Comparison Draka / Fraunhofer Institute predictions
Draka Comteq
Silica Expertise Group
Experimental results at high doses / diff. dose-rates
Figures issued from M. Van Uffelen’s PhD report
 According to M. Van Uffelen’s results, RIA curves are parallel in linear scale. That
means that the differences between curves obtained at different dose-rates is constant.
RIA prediction, ER| 13
Comparison Draka / Fraunhofer Institute predictions
Draka Comteq
Silica Expertise Group
Comparison Draka’s model / experimental results at high doses
100
RIA [dB/km]
80
60
40
20
0
0.0E+00 5.0E+03 1.0E+04 1.5E+04 2.0E+04 2.5E+04 3.0E+04 3.5E+04 4.0E+04
Dose [Gy]
140
120
RIA [dB/km]
100
80
60
40
20
0
0.0E+00
5.0E+04
1.0E+05
1.5E+05
Dose [Gy]
2.0E+05
2.5E+05
RIA prediction, ER| 14
Comparison Draka / Fraunhofer Institute predictions
Draka Comteq
Silica Expertise Group
Weak points of Draka model
• The model is valid only for l=1310nm, at RT.
•We have a big uncertainty on the non-reversible part (a factor 3 for dose =
100 000 Gy).
• Some fibers may have several reversible components.
• The model has to be adjusted for each fiber type => to do that, a few
experimental data are needed.
• How to reduce the uncertainty on the non-reversible part?
 attenuation measurement at 1310nm for 3 different doses (10, 103, 105 Gy),
after total annealing.
RIA prediction, ER| 15
Draka Comteq
Silica Expertise Group
Attenuation increase
Marcoussis
prediction
in CERN conditions
December 6th, 05
for DRAKA fibers
Silica Expertise Group
RIA prediction, ER| 16