holey silica-core fibres: an alternative fibre type for plasma diagnostic systems
DESCRIPTION
Fibre Optics Research Centre of the Russian Academy of Sciences (FORC). Holey Silica-Core Fibres: An Alternative Fibre Type for Plasma Diagnostic Systems. A.L.Tomashuk , A.F.Kosolapov and S.L.Semjonov [email protected]. 10th Meeting of the ITPA Topical Group on Diagnostics, - PowerPoint PPT PresentationTRANSCRIPT
1
Holey Silica-Core Fibres: An Alternative Fibre Type for Plasma Diagnostic Systems
A.L.Tomashuk, A.F.Kosolapov and S.L.Semjonov
10th Meeting of the ITPA Topical Group on Diagnostics, Moscow, Russia, 10-14 April, 2006
2
OUTLINE
1. Retrospective glance at the progress in the development of fibers for plasma diagnostics in ITER
2. Silica-core holey fibres: properties and potential advantages
3. In-situ radiation hardening of a holey fibre with H2 gas: the first experiment
4. CONCLUSION
3
1. Retrospective glance at the progress in the development of fibers for plasma diagnostics
4
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
1995 1997 1999 2001 2003 2005
420 nm
610 nm
1995 – US and RF HT comparison experiment. Low-OH, low-Cl fibres are found to be most rad-hard:
Russian KS-V4 and Japanese F-doped-silica fibres.
(D.L.Griscom, K.M.Golant, A.L.Tomashuk, D.V.Pavlov, Yu.A.Tarabrin, Appl. Phys. Lett., vol. 69, pp. 322-324 (1996))
Radiation-induced optical loss, dB/m/MGy
Wavelength:
5
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
1995 1997 1999 2001 2003 2005
420 nm
610 nm
1997 – H2-loading and pre-irradiation of polymer-coated fibres: significant reduction of radiation-induced optical absorption regardless of the type of silica in the core
(A.L.Tomashuk, E.M.Dianov, K.M.Golant, A.O.Rybaltovsky, IEEE Trans. Nucl. Sci., vol. 45, pp. 1575-1579 (1998))
Radiation-induced optical loss, dB/m/MGy
Wavelength:
6
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
1995 1997 1999 2001 2003 2005
420 nm
610 nm
2000 – EU–JA–RF HT ‘round-robin’ experiment: H2-loaded and pre-irradiated KU-1-silica fibre (“KU-1H2G”) showed the lowest radiation-induced absorption.
(B.Brichard et al, J. Nucl. Mater., vol. 329-333, pp. 1456-1460 (2004); T.Kakuta et al, J. Nucl. Mater., vol. 307-311, pp. 1277-1281 (2002))
Radiation-induced optical loss, dB/m/MGy
Wavelength:
7
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
1995 1997 1999 2001 2003 2005
420 nm
610 nm
2001 – H2-loaded hermetically Al-coated 100-μm-core fibre. Very high H2 content of 5.7∙1020 cm-3
(A.L.Tomashuk, K.M.Golant, E.M.Dianov et al., Patent RU2222032 (2004))
Radiation-induced optical loss, dB/m/MGy
Wavelength:
8
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
1995 1997 1999 2001 2003 2005
420 nm
610 nm
2003 – H2-loaded hermetically Al-coated 200-μm-core fibres. Testing in EU and RF. H2 content of ~ 1∙1019 cm-3
(B.Brichard, 7th ITPA Meeting, Hefei, China, 11-15 Oct. 2004)
Radiation-induced optical loss, dB/m/MGy
Wavelength:
9
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
1995 1997 1999 2001 2003 2005
420 nm
610 nm
Radiation-induced optical loss, dB/m/MGy
Wavelength:
2003 – H2-loaded hermetically Al-coated 200-μm-core fibres. Testing in EU and RF HT. H2 content of ~ 1∙1019 cm-3
A better result in RF HT owing to a higher temperature ? It was concluded that fibres CAN be used inside the cryostat.
(A.Krasilnikov, 6th ITPA Meeting, Naka, Japan, 19-21 Feb. 2004; A.V.Bondarenko et al., Instruments and Experimental Techniques,vol. 49, pp. 190-198 (2006));
10
H-associated colour centres
• H2-loading may give rise to H-associated colour centres (!!!), if1) the initial H2 content is small, or 2) all H2 molecules haveentered into the silica networkunder radiation at high doses.
• Fortunately, these centres are healed by hydrogen as well.
400 500 600 700 8000
2
4
6
8
KS-4V+H2
KU-1+H2
KS-4V
KU-14.3 MGy
indu
ced
loss
, dB
/m
wavelength, nm
11
H-associated colour centres
• H2-loading may give rise to H-associated colour centres (!!!),
FORMATION by hydrogen:
H2 + γ → H + H
=Si: + H → =Si• –H
≡Si–Si≡ + H + γ → ≡Si–H…≡Si•
H(I)-centre
E’β-centre
400 500 600 700 8000
2
4
6
8
KS-4V+H2
KU-1+H2
KS-4V
KU-14.3 MGy
indu
ced
loss
, dB
/m
wavelength, nm
12
H-associated colour centres
• H2-loading may give rise to H-associated colour centres (!!!),
FORMATION by hydrogen:
H2 + γ → H + H
=Si: + H → =Si• –H
≡Si–Si≡ + H + γ → ≡Si–H…≡Si•
H(I)-centre
E’β-centre
SUPPRESION by hydrogen:
=Si• –H + H → =Si –H │ H≡Si–H…≡Si• + H → ≡Si–H + ≡Si–H
400 500 600 700 8000
2
4
6
8
KS-4V+H2
KU-1+H2
KS-4V
KU-14.3 MGy
indu
ced
loss
, dB
/m
wavelength, nm
13
H-associated colour centres
• H2-loading may give rise to H-associated colour centres (!!!),
Practical conclusions:
1) The initial H2 contentshould be as high as possible (≥ 1∙1020 cm-3),
or, what is better,
2) the H2 reservoir in silicashould be replenishedin-situ.
400 500 600 700 8000
2
4
6
8
KS-4V+H2
KU-1+H2
KS-4V
KU-14.3 MGy
indu
ced
loss
, dB
/m
wavelength, nm
14
Thus, the state of the art of the development of rad-hard fibres is: Thus, the state of the art of the development of rad-hard fibres is:
1. Fibres to be installed inside the cryostat should be radiation-hardened via H2-loading;
2. H2-loaded hermetically Al-coated fibres are expected to withstand the radiation field inside the cryostat; 3. The initial H2 concentration should be as high as possible (≥ 1020 cm-3); otherwise, growth of loss in the blue region may occur; 4. It is desirable to have the possibility to load fibres with H2 in-situ, directly in the process of their operation in ITER.
15
2. Silica-core holey fibres: properties and potential advantages
16
500 600 700 8000
20
40
60 KU-1 silica in the core
Holey fibre
POD fibre
init
ial l
oss
, dB
/km
wavelength, nm
2. Silica-core holey fibres: properties and potential advantages
• possibility to supply H2 gas into the core in-situ through the holes• low cost of preforms in quantity production• high aperture
17
60Co rods
fibre coils
H2 pressure of 42 atm.
3. In-situ radiation hardening of a holey fibre with H2 gas: the first experiment
• Fibre coils were immediately in the water: unexpected effect of radiolythic H2
coming from the water pool
• H2 pressure was just 42 atm. It can be increased by many times. holey fibre is
connected to a hole-free fibre
holey fibre isspliced with a hole-free fibre
18
3. In-situ radiation hardening of a holey fibre with H2 gas: the first experiment
400 500 600 700 800
0,0
0,5
1,0
1,5
2,0
2,5
3,0
ind
uce
d lo
ss, d
B/m
wavelength, nm
730 kGy
8 kGy
570 kGy
140 kGy
H2-loaded holey fibre
• Very efficient suppression of the 610 nm band.
• Big H-associated absorption at short wavelengths, which decreases with dose!!!
• H2 pressure and dose should be increased in the next experiment (≥ 120 atm. and > 1 MGy).
19
Comparison with H2-free KU-1 fibres irradiated at the same time
λ=400 nm
H2-loaded holey fibre
holey fibre without H2
POD-fibre without H2 H2-loaded holey fibre
POD-fibre without H2
holey fibre without H2
λ=400 nm λ=610 nm
• Non-monotonic behavior of the ‘H2-free’ fibres is due to H2 penetration from the water pool.
• H2-loaded holey fibre: not only the 610 nm band, but also the short-wavelength absorption are gradually suppressed even at just 42 atm. H2 pressure in the holes.
20
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
1995 1997 1999 2001 2003 2005
420 nm
610 nm
Radiation-induced optical loss, dB/m/MGy
Wavelength:
2006 – Silica-core holey fibre loaded with H2 in-situ.
• Ultra-low induced loss at 610 nm!
• Suppresion of the short-wavelength absorption is likely to be achieved at a higher H2 pressure (≥ 120
atm.)
The 610 nm bandis suppressed almostcompletely (< 0,01 dB/m)!
21
CONCLUSION
A closer look should be taken at silica-core holey fibres.
Loading such fibres with H2 in-situ using the longitudinal holesopens up a possibility to significantly prolong the fibre’s life-timeinside the cryostat.
Increasing the H2 gas pressure in the holes from 42 atm. used in our experiment to ~ 120 atm. and over will allow further reduction of the radiation-induced loss in the red region and is likely to lead to suppression of the short-wavelength radiation-induced absorption.
Such an experiment under high-dose (> 1 MGy) γ- or reactor irradiation would be of much physical and practical interest.