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Radiation tolerant fibres for LHC controls and communications

This project aims to verify and characterize the radiation effects on optical fibres used in the LHC. Results include the identification of alternative fibres with better radiation resistance and modeling of radiation-induced loss at different dose rates.

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Radiation tolerant fibres for LHC controls and communications

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  1. Radiation tolerant fibres for LHC controls and communications • Jochen Kuhnhenn • Fraunhofer INTAppelsgarten 2D-53879 EuskirchenGermany

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

  3. Introduction • Introduction • 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 1 000 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 • Dose rate: 0.22 Gy/s • Dose: 10 000 Gy • Room temperature • Wavelength: 1310 nm • Light power: ~ 10 µW • Detailed tests • Dose rate: 0.016 Gy/s  3.7 Gy/s • Dose: up to 150 000 Gy • Wavelengths: 1310 & 1550 nm • Light power: up to 300 µW

  12. Results • Introduction • Project overview • Results • 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. Draka New better Fujikura better Comparison of dose rate dependence of new fibres • Draka New • 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: 8 + 3 hours • 2.3×1016 total beam loss per year in IR7 • Dose in fibres ~ 10 000 Gy per 1016 protons(private communication: Wijnands, Kurochkin) • Expected radiation environment for optical fibres in IR7 • Maximum averaged dose per year: ~ 23 000 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 20+10 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 2 D-53879 Eurkichen Germany Tel.: +49(2251)18200 Fax: +49(2251)18378 Email: kuhnhenn@int.fhg.de

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