1. Distributed Optical Fibre Radiation and Temperature Sensor (DOFRS)
Iacopo Toccafondo, EN-EA

2. Outline Introduction & Motivations
Distributed Optical Fiber Radiation Sensor (DOFRS) based on RIA
Distributed radiation measurements at CHARM
PSB Installation & Further Work

3. Introduction Concerns High radiation levels
Ensuring reliability and safety of the accelerator complex
Equipment groups rely on accurate dosimetry for lifetime prediction
Currently
Monitoring systems
Designing and installing radiation resistant components
Regular maintenance, replacement/relocalization
Limitations
Monitoring systems are discrete/punctual, only partially online
Frequent maintenance due to conservative life estimation approach

4. Motivation
Provide accurate online distributed dosimetry
Increasing safety
Cost-effective implementation
Future collider projects
=> Necessity of a cost-efficient, implementable and performant solution!

5. Concept - Distributed measurements
Conventional (discrete)
Optical Fibre Based
(distributed)
Online monitoring
< 1m spatial resolution

6. Radiation effects on Silica-based optical fibers
Radiation Induced Attenuation (RIA): increase in the glass linear attenuation through an increase of the linear absorption due to radiation-induced defects.
Impact on RIA:
The fiber composition an structure:
Co-dopants such as germanium (Ge), phosphorus (P), aluminum (Al), fluorine (F) = > different radiation response
Single or multi-mode
Radiative environment characteristics:
Dose dependency
Dose rate dependency
Temperature dependency
Application parameters:
Launched optical power
wavelength
E. Regnier et al., “Low-Dose Radiation-Induced Attenuation at InfraRed Wavelengths for P-Doped, Ge-Doped and Pure-Silica-Core Optical Fibres”, IEEE Transactions on Nuclear Science, Vol. 54., NO 4, August 2007

7. Distributed Optical Fiber Radiation Sensor (DOFRS) based on RIA
Optical Time Domain Reflectometry
OTDR based
Control Unit
Optical Fibre
Backscattered light
Distance (km)
Light Intensity
(dB)

8. Distributed Optical Fiber Radiation Sensor (DOFRS) based on RIA
Optical fibre based radiation sensing
Ionizing
radiation
OTDR based
Control Unit
Conventional
Distance (km)
Light Intensity
(dB)
Distance (km)
Dose (Gy)

9. Distributed OTDR radiation sensing at CHARM
24 GeV/c, p
130 m long fibre path
Two heights around the shielding:
95 cm & 280 cm above ground
Wide range of dose rates
Target
Optical Fibre
Adapted from the CHARM facility webpage
Equipment: EXFO FTB500 with two high dynamic range OTDR modules
SMF (850 nm & 1300 nm) & MMF (1310 nm & 1550 nm)
Available pulse duration: 5 ns up to 20 µs
Measurement time: 30 s up to 180 s

10. Distributed OTDR radiation sensing at CHARM
J-fiber MMF, pulse width: 10 ns, acquisition time: 30 s, Al-h target
Correct detection and localization of the four major dose peaks
Detecting dose variations down to Gy

11. Distributed OTDR radiation sensing at CHARM
J-fiber MMF, pulse width: 10 ns, acquisition time: 180 s, Cu target
After 10 h 37 min

12. Distributed OTDR radiation sensing at CHARM
J-fiber MMF, pulse width: 10 ns, acquisition time: 180 s, Cu target
After 16 h 37 min

13. Distributed OTDR radiation sensing at CHARM
J-fiber MMF, pulse width: 10 ns, acquisition time: 180 s, Cu target
After 25 h 57 min

14. Test installation in the PSB
First in-field deployment at CERN: installation in the Proton Synchrotron Booster (PSB)
Targeting full coverage (~157 m)
Dose range from few tens Gy/y
up to 100 kGy/y
Up to a factor
10 reduction
J.P. Saraiva and M.Brugger,
“CERN-ACC-NOTE ”, 2015
Post LS2, LINAC4 => reaching 2 GeV!

15. Test installation in the PSB - Status
Approved Engineering Change Request (ECR)
Installation of a metallic structure to support control RACK during week 37
Installation of RACK and fibre infrastructure during the EYETS
Installation and testing of equipment, end of EYETS

16. Further Work – Fibre Selection
Characterizing commercial optical fibres
At CC60 and CHARM facilities (CERN)
Outside: Fraunhofer INT, others
Purchasing from Fibrecore (P-doped cladding) and LEONI, any other?
Corning doesn’t have any radiation sensitive fibre
Draka (Italy) neither...
OFS has a does rate dependency
Characterizing optical fibres from ixBlue
Fibres co-designed by LHCurien St-Etienne => highly promising
PCe fibres – starting 14/09/2016 at CHARM
P-doped => testing at CHARM?
HACC => testing at CHARM?
Designing optical fibres with ixBlue and LHCurien

17. Development of customized control unit - Status
Meeting with Scuola Superiore Sant’Anna and INFIBRA Technologies held in Pisa on the 27/05/2016 => discussed two possible approaches
Control unit: necessary hardware and software developed and configure to control two commercially available sensors => OTDR + Raman DTS
=> Market survey being carried out to assess if commercially OTDR boards are available and at what cost - ongoing
Hybrid solution: adapting an existing highly performant Raman DTS developed by INFIBRA to be also used as OTDR
=> photobleaching effects due to coding need to be assessed – to be started

18. Development of customized control unit - Status
Acquisition, data processing and results visualization interface, currently being developed in Python - ongoing
EN/STI-ECE will take over the LabView implementation of the above and TIMBER logging => useful both for PSB and possibly for the custom control unit

19. Open Questions
For a chosen fibre, would it be worth studying the possible impact of radiation type? Protons, neutrons, gamma etc...
Systematic study of photobleaching on a P-doped fibre
For a given launched optical wavelength do we only bleach the associated/corresponding color center or also others?
Influence of coding (train of pulses) on photobleaching effects?

20. Many thanks for your attention!