1. Radiation tolerant fibres for LHC controls and communications
Jochen Kuhnhenn
Fraunhofer INT Appelsgarten 2 D Euskirchen Germany

2. Outline
Introduction
Project overview: "Radiation tolerant fibres for LHC"
Results
Conclusions

3. Introduction Introduction Project overview Results Conclusions
Motivation
The Fraunhofer Institute at a glance
Radiation effects on optical fibres
Project overview
Results
Conclusions

4. Motivation More than 1 500 km of optical cables needed for LHC
Control and communication
Beam instrumentation
Advantages of optical communication
Extreme noise immunity and ground potential independence
Lower attenuation (no repeater needed)
Higher flexibility (additional links on demand without tunnel access)
In LHC cleaning insertions IR3 and IR7 high radiation levels expected from day 1
First tests of installed fibres led to concerns if continuous transmission will be possible (Wijnands et al.: LHC Project Note 351, Presentation at 4th LHC radiation workshop)

5. The Fraunhofer INT
Experience of more than 30 years on effects of nuclear radiation on electronics and opto-electronics
The institute operates several irradiation facilities (Co-60, 14 MeV neutrons, flash X-Rays, access to 35 MeV protons)
Offering irradiation services to governmental, scientific, and industrial customers including planning and interpretation
Full range of measurement equipment for characterisation and analysis of radiation effects in electronics and opto-electronics
One focus: Radiation effects on optical fibres
Tested several fibres of all types and manufacturers
Close contacts to fibre manufacturers and research institutions

6. Radiation effects on optical fibres
Ionising radiation changes every property of an optical fibre
Refractive index
Bandwidth
Mechanical properties (e.g., tensile strength)
Additional: Generation of luminescence light
These effects show up typically only at relatively high doses or dose rates
Most obvious and disturbing effect is the increase of attenuation

7. Parameter dependencies of RIA
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
Temperature

8. "Radiation tolerant fibres for LHC": Project overview
Introduction
Project overview
Aims
Approach
Experimental details
Results
Conclusions

9. Project aims
Verification of previous irradiation tests of currently installed optical fibres by Draka
Full characterisation of radiation effects in used Ge-doped Draka fibre
Identification of optical fibres with better radiation resistance
Modelling of radiation induced loss at different dose rates

10. Project steps Acquisition of possible alternative optical fibres
Screening test of all samples under identical conditions
Fixed dose, dose rate, temperature, light power, wavelength
Detailed testing of current Draka fibre and best two candidates
Variation of dose rate & dose, wavelength, light power
Accelerated simulation of LHC radiation environment

11. Experimental details Screening tests Detailed tests
Dose rate: 0.22 Gy/s
Dose: Gy
Room temperature
Wavelength: 1310 nm
Light power: ~ 10 µW
Detailed tests
Dose rate: Gy/s  3.7 Gy/s
Dose: up to Gy
Wavelengths: 1310 & 1550 nm
Light power: up to 300 µW

12. Results Introduction Project overview Results Conclusions
Identification of alternative products
Screening tests of candidates
Detailed testing of now used fibre and best candidates
Modelling of dose rate dependence
Conclusions

13. Identification of other products
Fraunhofer INT contacted 10 manufacturers known for radiation resistant optical fibres
Of those 6 provided samples
Draka developed new fibre: "Draka New"
Heraeus
Fujikura
Corning
Manufacturer X
Manufacturer Y
Additional sample of current Ge-doped fibre "Draka #445755"

14. Results of candidate screening test
Logarithmic scale
Linear scale

15. Detailed tests of Draka #445755: Wavelength dependence

16. Detailed tests of Draka #445755: Dose rate dependence

17. Comparison of dose rate dependence of new fibres
Draka New
Fujikura
Draka New
better
Fujikura

18. Radiation induced loss of used and new fibres: Summary
Results for currently installed Ge-doped fibre by Draka
It is one of the best tested fibres of this type
1310 nm has advantages for doses higher than 6000 Gy
Increased light power does not improve radiation resistance (not shown in slides)
Two new candidates characterised with focus on dose rate dependence
Both candidates show better radiation tolerance for higher doses
Draka New better at least by a factor of 2 for highest doses
Fujikura better above 10 Gy with best performance (by a factor of 10) between 100 and 1000 Gy

19. LHC operation conditions assumed for loss modelling
LHC Project Note 375
One LHC year: 140 days of physics
Assumptions
“Nominal” physics
Fill length + Turn around: hours
2.3×1016 total beam loss per year in IR7
Dose in fibres ~ Gy per 1016 protons (private communication: Wijnands, Kurochkin)
Expected radiation environment for optical fibres in IR7
Maximum averaged dose per year: ~ Gy
Maximum mean dose rate: 2 mGy/s
Peak dose rates expected to be much higher

20. Extrapolated losses for maximum mean LHC dose rate

21. Accelerated simulation of LHC conditions
Acceleration by factor 10 for operation:
Irradiation for 2 hours at ~ 20 mG/s
Annealing for 1 hour
Repeating 10 times
Same dose per cycle (~ 150 Gy) as expected for LHC
Simulates nearly two weeks of LHC operation
Comparison of cyclic irradiation with results of continuous irradiation at corresponding mean dose rate

22. Cyclic irradiation compared with continuous irradiation

23. Cyclic irradiation compared with continuous irradiation

24. Conclusions
Introduction
Project overview
Results
Conclusions

25. Conclusions
Currently installed Ge-doped Draka fibre can be operated for extended time (If average mean dose rate scaling is appropriate)
Both new candidates show better radiation tolerance (Extend depending on dose range)
Cyclic irradiations with annealing periods do not lead to a attenuation increase as the corresponding continuous irradiation
Better understanding of realistic conditions at LHC needs time-dependent dose rate data and further investigations

26. Thank you very much for your attention
I’m looking forward to your questions …
Contact: Dr. Jochen Kuhnhenn Fraunhofer INT Appelgarten D Eurkichen Germany Tel.: +49(2251) Fax: +49(2251)