Radiation tolerant fibres for LHC controls and communications Jochen Kuhnhenn Fraunhofer INT Appelsgarten 2 D-53879 Euskirchen Germany

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

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

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)

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

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

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

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

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

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

Experimental details Screening tests Detailed 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

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

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"

Results of candidate screening test Logarithmic scale Linear scale

Detailed tests of Draka #445755: Wavelength dependence

Detailed tests of Draka #445755: Dose rate dependence

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

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

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

Extrapolated losses for maximum mean LHC dose rate

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

Cyclic irradiation compared with continuous irradiation

Cyclic irradiation compared with continuous irradiation

Conclusions Introduction Project overview Results Conclusions

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

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