Radiation Tolerant Optical Fibres for LHC Beam Instrumentation
Radiation Effects
T. Wijnands†, L.K. De Jonge†, J. Kuhnhenn‡, S. K. Hoeffgen‡, U. Weinand‡
†CERN, TS Department‡ Fraunhofer INT Euskirchen Germany
29-30 September 2007 6th LHC Radiation Workshop 2
Silica
• Silica (SiO2) exists in– crystalline form
– amorphous form (a-SiO2)
(amorphous : no long range order)
• a-SiO2 is easily formed :– bond angle can vary by ~70– rotation of bond is nearly free
29-30 September 2007 6th LHC Radiation Workshop 3
Silica Optical Fibers
• Fibres are long ‘drawn’ strands of silica• Fibre drawing generates additional disorder via
– irregular arrangements of Si and O in the lattice– impurity atoms (such as OH)
• Random structure leads to – light scattering – light absorption
• Dopants – to modify refractive index – to modify attenuation spectrum
29-30 September 2007 6th LHC Radiation Workshop 4
Color defects
• Color defects lead to optical absorption bands– Silanonol absorbs at 1380 nm (“water peak”)
(SiOH group from hydrogen pollution)
• Radiation creates additional color defects via– radiolysis mechanism (ionisation)– knock on mechanism (displacement)
29-30 September 2007 6th LHC Radiation Workshop 5
Optical fiber loss components
SiOH
AbsorptionScattering
-4
29-30 September 2007 6th LHC Radiation Workshop 6
Experimental techniques
Study radiation induced defects via :• Photoluminescence• Electron Spin Resonance• Optical attenuation measurements
– at fixed wavelengths (here 1310 and 1550 nm)– for complete spectrum (here only at beginning/end)
29-30 September 2007 6th LHC Radiation Workshop 7
Radiation tests in 1999-2000
Radiation Induced Attenuation (RIA) :
• SM fibre 1330 nm 0.1 dB/km per Gy
• LHC Tunnel (ARCs) : 10 Gy per year
29-30 September 2007 6th LHC Radiation Workshop 8
Collimation areas LHC
• Monte Carlo simulations (2005)– Fibres exposed to ~10 kGy/year
• Requirement :– RIA cannot exceed 6 dB total
for BPM analog signals– ~500 m fibre length exposed
This was a reason for concern :• 6 dB would be reached in 2.4 days LHC operation• For 10 yrs LHC we would need factor 1000 better• How about the ducts and blowing with oil ?
Surface Building
Acces shaft
Underground Tunnel
Underground Galery
Optical fiber
Acknowledgement : R. Schmidt
29-30 September 2007 6th LHC Radiation Workshop 9
60Co irradiation test standard SM LHC fibres
• Material testing for duct blowing technique • Attenuation at 1310 nm in fibres for tunnel in :
– Ge-P doped MCVD (Draka NK Cables Ltd)– Ge-doped PCVD (Draka Fibre Technology BV)
29-30 September 2007 6th LHC Radiation Workshop 10
Optical absorption in standard LHC SM fibres
Ge-doped
Ge-P doped
no irradiation
no irradiation Co-60
1 kGy/hr
Co-60
500 Gy/hr
29-30 September 2007 6th LHC Radiation Workshop 11
RIA in Ge-doped SM fibres
• In GeO2 fibres :– Ge(0), …, Ge(3) defects
(0,..,3 electrons trapped at O vacancies of Ge-ions)– Ge(0) and Ge(3) much lower in concentration
compared to Ge(1) and Ge(2)– 100-450 nm absorption bands
• Annealing– detrapping of the electrons– Ge(3) trap is deeper than G(2) and so on– Ge(3) gives residual attenuation
E.J. Friebele et al, J. Appl. Phys. Vol. 45 No.8 July 1974
29-30 September 2007 6th LHC Radiation Workshop 12
Optical absorption in standard LHC SM fibres
Ge-doped
Ge-P doped
no irradiation
no irradiation Co-60
1 kGy/hr
Co-60
500 Gy/hr
29-30 September 2007 6th LHC Radiation Workshop 13
RIA in Ge-P doped SM fibres
• In pure SiO2 - P2O5 fibres :– P1, P2, P3, P4, POHC and S defects observed– Absorption via P1 effect dominates at 1450 nm :
• PO32- molecular ions
– Annealing :• POHC decrease and PO3
2- increase
• all others constant
O
O
O
P
Griscom et al, J. Appl. Phys. Vol. 54 No.7 July 1983
29-30 September 2007 6th LHC Radiation Workshop 14
Optical Fibre irradiation tests – Fraunhofer INT
Sample preparation (video)
Fibre Splicing
29-30 September 2007 6th LHC Radiation Workshop 15
Screening test at Fraunhofer INT
Fusion sp lices
60C o
VariableAttenuator
LED/LDSource
2-Ch opticalPower m eter
BA
Con
nect
ors
C oupler
Lead box
Lead tubes
C oncrete sh ie ld ing
LabView controlleddata acquis ition system
GP
IB
Control com puter forrem ote access
E thernet
T herm ally s tab ilized m easurem ent booth
T est fibre spool
G am m am at TK1000(m ax. 600 C i 60Co)
F ibre optic cables
29-30 September 2007 6th LHC Radiation Workshop 16
Radiation Induced attenuation
0 2000 4000 6000 8000 10000
0
5
10
15
20
25
30
35
40
Ge-doped 1,2,3 PSC 1,2 Unknown F-doped
Indu
ced
Loss
[dB
/km
]
Dose [Gy(SiO2)]
=1310 nm, D=104 Gy, D=0.2 Gy/s, T=24-28°C, l=50-200 m, P=10/40 µW
1
3
2
2
1
29-30 September 2007 6th LHC Radiation Workshop 17
Standard Ge-doped SM fiber
10-2 10-1 100 101 102 103 104 105
0.1
1
10
100
1
3.0 Gy/s
1.4 Gy/s
0.2 Gy/s
Indu
ced
Loss
[dB
/km
]
Dose [Gy(SiO2)]
Dose rate variationParameter variation(1): Wavelength(2): Lightpower
2
0.02 Gy/s
1
2
29-30 September 2007 6th LHC Radiation Workshop 18
Radiation hardened F-doped fiber
10-2 10-1 100 101 102 103 104 105
0.1
1
3.0 Gy/s
1.4 Gy/s
0.2 Gy/s
Indu
ced
Loss
[dB
/km
]
Dose [Gy(SiO2)]
Dose rate variationParameter variation(1): Wavelength(2): Lightpower(3): Temperature
1
2
3
0.02 Gy/s
1
2
3
29-30 September 2007 6th LHC Radiation Workshop 19
High Energy Physics irradiation test at CERN
Fusion splices
1x8 PLCCoupler
LED/LDSource
2-Ch opticalPower meter
BA
LabView controlleddata acquisition system
GP
IB
Control computer forremote access Internet
Measurement booth
Up to 7 test fibre spools
16 Fibres in 72-way cable
1x8 MEMSSwitch
LightShutter
OTDR
Return fibres in 72-way cable
Inward fibres in 72-way cable
Lead cable reference fibre
Reference fibre
Beam
29-30 September 2007 6th LHC Radiation Workshop 20
LHC Radiation Test Facility (TCC2)
29-30 September 2007 6th LHC Radiation Workshop 21
High Energy Physics Radiation field
0 200 400 600 800 1000 1200 1400 1600 1800 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Indu
ced
Loss
[dB
/km
]
Dose [Gy]
Ge-doped Unknown F-doped
29-30 September 2007 6th LHC Radiation Workshop 22
High Energy Physics radiation field vs 60Co
0.1 1 10 100 1000
0.01
0.1
1
Complex field:
Indu
ced
Loss
[dB
/km
]
Dose [Gy]
Ge-doped Unknown F-doped
Complex field
60CoD1.8 kGy/d
D5 Gy/d D23 Gy/d
29-30 September 2007 6th LHC Radiation Workshop 23
SM fibres Fujikura Ltd Japan
• Radiation hardening via :– F-doping– Special manufacturing process– H-loading ?
29-30 September 2007 6th LHC Radiation Workshop 24
F-doping
What are the positive effects of Fluorine doping ?– Quenches defects absorbing in the short wavelength region– Breaking of strained bonds (reduction of disorder)– Increase of band gap energy– Reduction of glass viscosity
F-doping
F
F
K. Sanada et al , Journal of Non-Cryst. Solids 179 (1994) 339-344
Fluorine contents has an optimum !
29-30 September 2007 6th LHC Radiation Workshop 25
Reducing the SiOH impurity
• Silanol (SiOH) absorbs light between 1300-1500 nm• SiOH is produced via :
– NBOHC Defect + Hydrogen
Si - O• + •Ho Si – OHSi - O•
D.L. Griscom, J. of the Ceramic Soc. Japan, Int Edition Vol.99-903
29-30 September 2007 6th LHC Radiation Workshop 26
H – loading technique
• From literature :– H2 doping reduces losses of F-doped silica
– Large reduction in absorption peak at early stage of irradiation– Two staged process :
• H2 diffusion into the fibre core
• Reaction of H2 with existing defects
K. Sanada et al , Journal of Non-Cryst. Solids 179 (1994) 339-344
29-30 September 2007 6th LHC Radiation Workshop 27
Series sample testing (60Co) 1310 nm
0 20000 40000 60000 80000 100000
0
1
2
3
4
5
Sample #4 7S-0005/3
Indu
ced
Loss
[dB
/km
]
Dose [Gy(SiO2)]
Rapid defect generation from precursors
Slow diffusion process (involving H ?) and defect conversion
29-30 September 2007 6th LHC Radiation Workshop 28
Series samples testing (60Co) 1310 nm
29-30 September 2007 6th LHC Radiation Workshop 29
Conclusions• Radiation Effects in OF are complex• RIA in Co-60 and HEP radiation fields comparable
– radiolysis– knock on process– particle type– particle energy
• F-doped SM fibre Fujikura Ltd shows excellent performance• QA production lot acceptable• RIA < 5 dB/km at 1310 nm and 1550 nm (< 1 MGy)
unprecedented result – meets LHC BLM specifications !!!• Further studies are ongoing :
– What is the role of H ?– What is the annealing behavior ?– Spectral shifts ?
• Fibre monitoring in LHC IR3/IR7 is recommended