Radiation Effects on Optical Fibres at SCK CEN: Report and Proposal for ITER

1. Association Euratom-Belgium EFDA European Fusion Development Agreement Benot Brichard , Hans Ooms, Stan van Ierschot, Jean Pouders, Stan Hendrieckx Instrumentation Department Tel: +32 14 33 26 40 Secr: +32 14 33 26 07 Fax: +32 14 31 19 93 bbrichar@sckcen.be www.sckcen.be Report on radiation effects on optical fibres at SCK CEN: H 2 -loading, infrared-fibres and fibre current sensor Nuclear Belgian Research Center Boeretang, 200 2400 Mol Belgium

2. 2 Overview New fibre optic technology for ITER: a proposal Development & Irradiation testing of radiation-resistant fibres TW5-TPDC/IRRCER-Deliverable 1 & 2 Progress in on-going EFDA-IRRCER fibre-related tasks IR fibres for thermography application: gamma radiation-sensitivity TW4-TPDC/IRRCER-Deliverable 16 fiber current sensor behaviour at cryogenic temperature TW5-TPDC/IRRCER-Deliverable 9

3. 3 Defects and imperfections cause photons to be absorbed at specific wavelengths in fibres Radiation creates additional or new defects Wavelength [nm] IR phonon absorption edge UV edge Si-OH Rayleigh scattering ~ Drawing defects Waveguide imperfections 10 4 10 2 1 200 600 1000 1400 1800 2200 Intrinsic spectral absorption in silica fibre dB/km Total intrinsic optical absorption < 0.6 m > 10 -2 dB/m 1.8 m > > 1 m < 1x10 -3 dB/m

4. 4 Two categories of defects in SiO 2 Paramagnetic Centres E NBOHC POR (SPOR) STH Detected by EPR/ESR spectroscopy Diamagnetic Centres Oxygen Deficient Centre (ODC) Si-Si OA: 5 eV PL: 7.6 eV Peroxy Linkage (POL) Si-O-O-Si OA: 7.1 eV ? (recent assignment) Can act as defect precursors for paramagnetic defects Only indirect optical evidences

5. 5 Radiation affects the optical properties of silica Radiation-Induced Absorption ( RIA ) Due to defect formations: E,NBOHC,POR,STH, Radiation-Induced Luminescence ( RIL ) Due to Photoluminescence Due to Cherenkov effect in SiO 2 Radiation-Induced Refractive Index Change (RIRIC) Compaction-densification Colour centres

6. 6 H 2 -treatment drastically reduces the 2 eV RIA band formation in all type of fibres Fissionreactor irradiation of High OH silica fibres 200 m core Acrylate coated B. Brichard, A. L. Tomashuk & al., SCK CEN, J. of Nucl. Mat., 329, p1456, 2004

7. 7 394 kGy 1.6 MGy 55 kGy 394 kGy 1.6 MGy H 2 slows down the RIA growth at 600 nm while OH content is enhanced at the same time 550 670 790 1030 1390 550 670 790 1030 1390 Wavelength [nm] RIA [dB/m] 55 kGy 0 0.25 0.5 0.75 1 1.25 1.5 Wavelength [nm] Low OH silica with H 2 Low OH silica without H 2 + 0.4 eV 0 2 H OH Si H O Si 0.1 eV

8. 8 STU +H2 1. STU-200 m + H2 At low dose the H 2 -STU fibre showed the best radiation-resistance Radiation-hardness factor @ 600 nm Ranking @ 600 nm 5x10 15 n/cm2 ; 200 kGy 330 Gy/s ; 60C ~3 MGy (pre-ionised) Wavelength [nm] RIA [dB/m] 10 400 600 1000 1400 0 5 10 OH growth KSV4 +H2 2. KS4V-200 m KU1 +H2 3. KU1-200 m STU 5. STU-200 m SSU +H2 (600 m) 4. SSU-600 m

9. 9 When the H 2 is exhausted RIA quickly re-increases 7.12x10 17 n/cm 2 23 MGY 80C Wavelength [nm] STU+H2 KS4V+H2 600 1000 1400 30 STU KU1+H2 and STU RIA [dB/m] 0 5 15 With these Al-coated H 2 - loaded fibres we can enter the cryostat but probably not far into the diagnostic block, unless we could change the fibres. Looking for improvement ?

10. 10 How to keep H 2 into the glass network ?

11. 11 We follow two complementary but different strategies The previous results demonstrate the clear advantage of treating silica optical fibres with hydrogen to improve the radiation resistance of the optical transmission in the visible spectral region. However, the optical transmission start degrading again as soon as the hydrogen is exhausted. Heavy H 2 PRE-LOADING Hermetic coating 300C, 300 bars This approach is currently on-going in Troistk, Moscow (cf collaboration EU/RF) in-situ H 2 RE-FUELING Permeable coating H 2 filling-line This approach is currently under study at SCKCEN (cf TW5-TPDC/IRRCER-Del 1 & 2)

12. 12 SMIRNOF VI irradiation device upgrade for handling depleted-H 2 atmosphere in reactor Fibres Thermocouples In-pile capsule Fibres are protected in stainless steal tubes filled with H 2 -depleted in anaerobic atmosphere pressure 10-20 bars temperature max 100C Continuous H 2 flow => licensing OK for reactor test

13. 13 A two step irradiation Irradiation 1 10 % Irradiation 2 40 % time 2 h 2 h 2 h Neutron flux: 1.7x10 14 n/cm 2 s Epithermal flux: 4.6x10 13 n/cm 2 s Fast neutron flux (>1 Mev): 1.9x10 13 n/cm 2 s Gamma Heating: 3 W/g[Al] Irradiation conditions in BR2-SIDONIE irradiation channel at full power (56 MW) neutron (~ 1 MeV) : 1.5 10 16 n/cm 2 gamma : 2.2 MGy neutron (~ 1 MeV) : 5.7 10 16 n/cm 2 gamma : 11 MGy

14. 14 Overview New fibre optic technology for ITER: a proposal Development & Irradiation testing of radiation-resistant fibres TW5-TPDC/IRRCER-Deliverable 1 & 2 Progress in on-going EFDA-IRRCER fibre-related tasks IR fibres for thermography application: gamma radiation-sensitivity TW4-TPDC/IRRCER-Deliverable 16 fiber current sensor behaviour at cryogenic temperature TW5-TPDC/IRRCER-Deliverable 9

15. 15 Divertor thermography with IR fibres Divertor Cassette Divertor Cassette is a high temperature region to be continuously monitored for machine protection IR fibre ? IR thermography proposed by CEA- Cadarache Tore-Supra

16. 16 IR-Fibres could be used to transport IR radiation from the divertor port to the bioshield Low OH Silica 1-2 m Sapphire 1-3.5 m max 3 m ZrF 4 1-4 m Up to 250C Chalcogenide 1-11 m Up to 150C Metal-coated fibres 3-17 m Low NA PBG fibres / Bragg Fibres ??? mirrors Cassegrain Telescope Fibres 8.5 m up to Bioshield Large Wavelength Span At the divertor port ~10 19 n/cm 2 (E>0.1 MeV) ~ 1 Gy/s ; >10 MGy Line of Sight

17. 17 Experimental set up to measure on-line radiation-induced absorption in IR fibres IR Spectrometer Lock-in Labview DAQ Lamp CEA Acquisition (R. Reichle) Fibre RITA Irradiation container

18. 18 IR2 3.5 m 2 m IR2- Hafniumfluoride Radiation sensitivity depends on the wavelength and type of fluoride compound material used Wavelength in nm RIA dB/m 3 kGy Recovery ~17 h RIA decreases with increasing wavelength 3 kGy 5.2 kGy IR1- Zirconiumfluoride 2 m 0 1 2 3 4 RIA in dB/m IR1 0.0 4.0x10 4 8.0x10 4 1.2x10 5 1.6x10 5 Time in hours 3.5 m recovery recovery

19. 19 Similar RIA in ZrF4 fibre from other manufacturer. 3 kGy 5.2 kGy -5.0x10 4 0.0 5.0x10 4 1.0x10 5 1.5x10 5 2.0x10 5 2.5x10 5 3.0x10 5 3.5x10 5 0.0 0.5 1.0 1.5 2.0 2.5 Time in seconds RIA dB/m Zirconium Fluoride (RA6) - Polymicro 2 m 20 40 60 80 100 120 Temperature C Temperature increase favours RIA decrease. Recovery

20. 20 Hollow Waveguide Fibre: good radiation resistance but extremely sensitive to bending No change observed after 27 kGy ! Hollow Waveguide: 750 m core 2 meters Hollow Waveguide From Polymicro

21. 21 Preliminary Conlusion on IR fibres Still to test Saphirre Fibre (and Chalcogenide ?) For 1-2 m, low-OH pure silica is a good candidate. However, we need more data on neutron damage at 2 m Above 2 m, Zirconium/ Hafnium Fibre much more radiation-sensitive than silica Hollow-Waveguide, good candidate but high-intrinsic loss and difficult to handle Also looking for PBG (Bragg) silica fibre operating in 2-3 m

22. 22 Overview New fibre optic technology for ITER: a proposal Development & Irradiation testing of radiation-resistant fibres TW5-TPDC/IRRCER-Deliverable 1 & 2 fiber current sensor behaviour at cryogenic temperature TW5-TPDC/IRRCER-Deliverable 9 Progress in on-going EFDA-IRRCER fibre-related tasks IR fibres for thermography application: gamma radiation-sensitivity TW4-TPDC/IRRCER-Deliverable 16

23. 23 Optical Fiber Current sensor in ITER ? Conventional plasma current measurement system like Rogowski coils looses sensitivity in quasi steady state plasma Need to assess the influence of radiation and low temperature on the Verdet Constant Interest for Fibre Current Sensor ? Faraday Effect Magnetic Field rotates the incident polarization state by an amount proportional to the Verdet Constant V.

24. 24 Few publications talking about Fibre current sensor in TOKAMAK and S. Kasai, I. Sone, M. Abe, T. Nishitani, S. Tanaka, T. Yagi, N. Yokoo and S. Yamamoto, On-line Irradiation Tests on Sensing Fiber of Optical-fiber Current Transformer , JAERI-Research 2002-007, p130-144 N.M. Kozhevnikov, Y. Barmenkov, V.A. Belyakov, A. Medvedev, G. Razdobarin, Fiber-optic sensor for plasma current diagnostic in tokamaks, SPIE vol. 1584 Fiber Optic and Lasers IX (1991), p 138-144 Y. Barmenkov, F. Mendoza-Santoyo, Faraday plasma current sensor with compensation for reciprocal birefringence induced by mechanical perturbations, J. Appl. Research and Technology, Vol 1, No2, 2003, p157- 163 Commercially Available System exists for electrical power industry In the US, NxtPhase : http://www.nxtphase.com In Switzerland, ABB, Baden-Dttwil CH-5405, K.Bohnert, optics and lasers in Engineering, 43 (2005), 511-526

25. 25 The fibre current performance will depend on wavelengths, temperature and radiation We prefer to operate the fibre current sensor in the low sensitivity region, i.e. 1.3-1.5 m, because at these wavelengths: we reduce the combined effect of radiation and low temperature we can more easily use an all- fibre optic sensor system A.H. Rose, JLT, Vol 15,n5,1997 Faraday Effect as Verdet constant in silica as function of wavelengths

26. 26 Mini-ITER Fibre Liquid Nitrogen Polarisation controller Current Source Light Source No data on Verdet Constant in Liquid Nitrogen

27. 27 Cryogenic Temperature induces decrease in sensitivity additional noise 0 5 10 15 20 25 30 35 Time in seconds I = 40 A => DOP ~ 3% - I + I 300 K Fiber current sensitivity slightly decreases when subjected to liquid nitrogen temperature I = 40 A => DOP ~ 2% - 77 K

28. 28 Preliminary conclusion on fibre current sensor Preliminary result is encouraging At liquid nitrogen temperature we observed a slight decrease of the fibre sensitivity with an increase of the noise in the measure => need optimizatiion Need to verify now the RIA of the fibre at 1.5 m at -77K if the radiation could degrade the Verdet constant

29. 29 Overview New fibre optic technology for ITER: a proposal Development & Irradiation testing of radiation-resistant fibres TW5-TPDC/IRRCER-Deliverable 1 & 2 Progress in on-going EFDA-IRRCER fibre-related tasks IR fibres for thermography application: gamma radiation-sensitivity TW4-TPDC/IRRCER-Deliverable 16 fiber current sensor behaviour at cryogenic temperature TW5-TPDC/IRRCER-Deliverable 9

30. 30 New fibre optic technology for ITER ?

31. 31 Photonic Crystal Fibres can be classified in two different families II. High Index Guiding Fibers - LICF Due to the Band Gap feature, light is exclusively guided into a hollow core characterised by low index Low intrinsic absorption is now available 0.1 dB/m @ 1550 nm 1 dB/m @ 500 nm I. High Index Guiding Fibers - HICF Light is guided in a solid core with higher refractive index than cladding Strong wavelength dependence of the effective refractive index Low intrinsic absorption 1.5 dB/km @ 1550 nm 30 dB/km @ 500 nm High NA > 0.6

32. 32 Function of reactor power Reactor Time 200 m Photoluminescence (O 2 ) 0.1 nW level at detector side Light intensity @ detector side [pW] RIA Cerenkov Wavelength [nm] Cherenkov and Photoluminescence Radiation induces Photo and Radio Luminescence in silica based material Luminescence in 200 m core fibre 600 m 600 800 1200 dB Function of fibre diameter Wavelength [nm] 20 % 40 % 60 % 80 %

33. 33 High-Index Core Fibres (HICF) should reduce Cherenkov yield while holding good light coupling Coupled Power P ~ D 2 NA 2 Cerenkov Yield Y ~ D 2 With HICF we can reduce the fibre diameter while increasing the numerical aperture In addition holes provide a way to inject efficiently hydrogen to repair the fibre transmission Cf results of A.L. Tomashuk (FORC)

34. 34 Fibres might simplify design and maintenance in many diagnostic Small and compact space PMTs suffer Radiation and EMI => Move away PMTs and Use fibres Liquid Scintillators response After D. Marocco, ENEA Lower Vertical Neutron Camera -LVNC 10 collimators ; 35 mm

35. 35 Conclusion, perspectives and expectations R&D work will carry on Hydrogen-loading technique with engineering emphasis Outlook to new fibre technology, like Photonic Crystal Fibres Now, real need to interact with designers to implement fibre pathways in ITER