1. Optical Fiber Sensors for Cryogenic applications Presented by: Daniele Inaudi, CTO SMARTEC

2. Contents Fiber Optic sensors Sensing in Extreme Environments:
Cryogenic temperatures
Radiation environments
Vacuum
Strong magnetic fields and EM interferences
Application Examples

3. Fiber optic Sensors: Why?
Small size of sensors and cables
Great variety in the measurable parameters
Insensitive to EMI (Electro-Magnetic Interference)
Distributed and Multiplexed topologies
Can work reliably in demanding environments, including extreme temperatures, radiation and vacuum

4. Main FOS Technologies Fabry-Pérot Fiber Bragg Gratings SOFO
Strain, T, pressure, displacement
Fiber Bragg Gratings
Strain, Temperature, acceleration, tilt
SOFO
Deformations, curvature
Brillouin/Raman
Distributed strain and temperatures

5. Fiber Optic Sensor Types
Point Sensor: Fabry-Pérot
Quasi distributed (multiplexed): FBG
Long base: SOFO
Distributed: Brillouin and Raman

6. Fabry – Pérot Principle
Measurement is achieved by measuring the Fabry-Perot cavity length using white light interferometry
Fabry-Perot Cavity
Optical Fiber
Mirror

7. Fabry-Pérot Sensors
Strain
Temperature

8. Fabry-Pérot Sensors
Pressure
Displacement

9. Fiber Bragg Grating Sensors
The reflected wavelength depends on the strain and temperature of the fiber

10. Optical scattering in silica fibersλ0
T, ε
Scattered Light

11. Distributed Sensing Reading Unit 0m 1m 100m Position [m] 1000m e e
Temp. [°C] 0m
Distributed Sensor T2 1m
100m T1 e
1000m F
Position [m]
Strain [me] T2 e
40km

12. Structures at Cryogenic Temperature
LNG Pipelines
LNG Tanks
Superconducting Magnets
Physics (ITER)
Particle physics (CERN)
Bio-chemistry (spin-resonance)
Space-like condition testing

13. Cryogenics: Key features
Sensors for Cryogenic temperatures must exhibit the following features:
Use of appropriate materials to control differential thermal expansion coefficients
Ability to operate reliably even during fast temperature changes, e.g. shock immersion in liquid nitrogen
Survive multiple temperature cycles. SMARTEC sensors are cycled 10 times in liquid nitrogen
Low sensitivity to very large temperature changes

14. Radiation: Key features
Sensors for Radiation environments must exhibit the following features:
No degradation of materials due to radiation
No drift of measurements due to radiation effects: SMARTEC sensors tested at 5 MGray dose
No significant increase in fiber optical losses due to radiation: use of rad-hard fibers

15. Vacuum: Key features
Sensors for vacuum environments must exhibit the following features:
No degradation of materials due to vacuum
No drift of measurements due to vacuum
Availability of vacuum feed-though to connect optical fibers to atmospheric environment
No de-gassing from sensors
Ability to sustain multiple vacuum cycles and rapid pressure changes

16. Magnetic and EMI: Key features
Sensors for Strong magnetic fields and EMI environments must exhibit the following features:
No drift or noise on measurements due to EMI
Use of non magnetic materials: SMARTEC sensors have magnetic permeability < 1.05
Use of non-metallic cables to avoid induced currents and allow electrical isolation of the sensors

17. SMARTEC Extreme Sensors
Measurements:
Displacement:
Short range
Long range
Non-contact
Strain
Temperature
Local
Distributed
Technologies:
Fabry-Perot (FISO)
FBG (MuST)
SOFO (low-coherence interferometer)
Laser Distance Meter
Raman (DiTemp)

18. Displacement: Long/short range
Fabry-Perot
Fabry-Perot
FBG
FBG

19. Non-contact Distance Meter
SOFO
Laser distance Meter
SOFO

20. Strain
FBG
Fabry-Perot

21. Temperature
Distributed Raman
Fabry-Perot
FBG

22. SMARTEC Extreme Sensors
Accessories:
Vacuum feed-through
Cables:
Rad-hard fibers
PEEK coating
Non Metallic
Fiber bundles
Sensor covers and mounting

23. Qualification and Testing

24. Summary of testing specs
Temperature: 4.2K ( –269°C) to 80 °C
Temperature sensors: 10K to 80°C
Distributed T sensors: 80K to 300°C
Radiation: SMARTEC sensors were tested at 5 MGray (gamma)
Vacuum: 10-8 Torr
Magnetic Fields: 6 Tesla

25. SMARTEC Experience/Partners
Reference Projects:
ITER (International Thermonuclear Experimental Reactor)
CERN (European particle research center) LHC magnets
Oak Ridge Spallation Neutron Source, USA
LNG Tanks and pipelines
CryoBragg EU Project
Other (confidential)

26. CERN-LHC Dipoles

27. Measurement Aims
Measure the relative displacements of the cord-mass and the vacuum tube
Measurement base: mm
Measurement base: 1.5 to 300 °K
Cold mass contracts about 20 mm during cool-down: lateral displacement
Cold mass rotates
Measurement in vacuum
No direct optical access to the measurement zones

28. Sensor installation

29. Results: Cool down

30. ITER International project for new Fusion Reactor
Under construction in Cadarache (France)
Thermo-Mechanical instrumentation: sensors, 80% fiber optics
Contract awarded to SMARTEC / FiberSensing Consortium

31. ITER
Phase II contract for delivery of 700 sensors (strain, displacement, temperature)
3-year qualification program
Monitoring of super- conducting magnets and support structures

32. ITER Magnets instrumentation
Toroidal Field Coils

33. ITER Magnets instrumentation
Central Solenoid

34. ITER Magnets instrumentation
Feeders
Correction Coils

35. Superconducting Magnets

36. Test Results down to 4.2K

37. Influence of Magnetic field @6T

38. LNG Surface Storage
Huelva storage (Spain)

39. Surface Storage
Standard instrumentation in a surface storage

40. Permanent Instrumentation
Protection system for
the Fiber Optic sensor

41. Permanent Instrumentation
The Fiber Optic system

42. Conclusions Fiber Optic Sensors for extreme conditions: Qualified for:
Displacement (short, long, non-contact)
Strain
Temperature (point, distributed)
Qualified for:
Cryogenic temperatures
Radiations
Vacuum
Strong Magnetic fields and EMI
Numerous references and applications
Paper: ITER Instrumentation: