study of a silica aerogel for a cherenkov radiator
DESCRIPTION
Study of a Silica Aerogel for a Cherenkov Radiator. Ichiro Adachi KEK representing for the Belle Aerogel RICH R&D group 2007 October 15-20 RICH2007, Trieste, Italy. Outline. Introduction Silica Aerogel Production Optical Quality Improvements & Studies Transparancy - PowerPoint PPT PresentationTRANSCRIPT
Study of a Silica Aerogel for a Cherenkov Radiator
Ichiro Adachi
KEKrepresenting for the Belle Aerogel RICH R&D group
2007 October 15-20
RICH2007, Trieste, Italy
RICH2007, Trieste, Italy2
Outline
• Introduction
• Silica Aerogel Production
• Optical Quality Improvements & Studies Transparancy Refractive Index Uniformity
• Machining Possibility
• Further Developments
• Conclusions
RICH2007, Trieste, Italy3
Introduction
• Proximity focusing RICH with silica aerogel as Cherenkov radiator for new Belle forward PID upgrade program going on to replace the present threshold-type
aerogel Cherenkov counter
• Requirements for radiator Refractive index ~ 1.05 High transparency Hydrophobic
for long term stability
Reasonable block size Aerogel radiator
Position sensitive PDwith B=1.5Tesla
Readout electronics
Cherenkov photon
200mm
n=1.05
RICH2007, Trieste, Italy4
• Baseline aerogel tiling configuration
Cover ~3.6m2 area Use hexagonal-shape aerogel
block• Reduce possible photon loss a
t corner
Hexagon with 75-mm side ~220 tiles in total Make square shape block first Then, make it hexagon with wa
ter-jet cutting device, making full advantage of hydrophobic nature
Radiator Tiling Layout
420mm
1145mm
Hexagon shape
RICH2007, Trieste, Italy5
Silica Aerogel Production
• Production Method Sol-gel process
nSi(OR)4 + 4nH2O nSi(OH)4 + 4nH2O hydrolysisnSi(OH)4 (SiO2)n + 2nH2O condensation
Chemical treatment to make hydrophobic Supercritical drying
CO2 extraction method 31 degree Celsius and 7.5 MPa
• Optical Quality Transparency
T = T0*exp(-d/) where T is light intensity and d sample thickness Refractive index measured with Fraunhofer method These properties are strongly related to:
Chemical solvent Mixing ratio between them
3 dimensional network
RICH2007, Trieste, Italy6
History of Aerogel Production
20
50
tran
smis
sion
leng
th a
t 40
0nm
(m
m)
refractive index
1.010 1.040 1.070 1.100
1st generation:1970’s-1980’sTASSO/PETRA1.025 ~ 1.055
2nd generation:1992-2002Belle Aerogel counter/KEKB1.010 ~ 1.030new production methodhydrophobic
3rd generation:2002- A-RICH for Belle upgrade1.030 ~ 1.080new solventI
II
III
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Optical Transparency
0
2
4
6
8
10
12
57 59 61 63 65 67
n = 1.050 sample20 mm thickness
Transmission at 400nm (%)
transmission measurement for 20 mm thickness samples
n = 1.045 20 mm thickness
Target indexAveraged transmission
length at 400nm
1.045 46.6 1.4
1.050 40.4 1.1
1.055 32.8 1.1
1.060 28.9 0.7
T = T0 exp(–d/): trans.length
2 times higher than previous samples
C = 0.005 m4/cm
C ~ 0.005-6 m4/cm
RICH2007, Trieste, Italy8
Transmission Length
• Transparency for index ~ 1.04-1.06 samples almost doubled• Confirmed in a series of test beam experiments
2nd generation
0
10
20
30
40
50
60
1.02 1.04 1.06 1.08Refractive index
Transmision length(mm)
◆2005-2006▲2004■Before 2003
Transmission length at = 400nmprototype result with 3 GeV/c pions
2005 sample
2001 sample
n~1.050
photon yield is not limited by radiator transparency up to ~50mm
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Index Measurement
• Refractive index Measured with Fraunhofer method using 405nm laser
0
5
10
15
Measured index
1.050
1.045 1.055 1.060
Target index Measured
1.045 1.0446 ± 0.0002
1.050 1.0488 ± 0.0001
1.055 1.0533 ± 0.0003
1.060 1.0614 ± 0.0002
screen
deflection angle
405nm laser
aerogel sample
only edge of aerogel block is usedCheck other area with an independent way
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0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
108 108.5 109 109.5 110 110.5 111 111.5
Angle
Intensity
Index Scan Study (1)
• Relative weight for each composition in an aerogel was examined with XRF (X-ray fluorescence) analysis
• X-ray tomography device was used to scan relative aerogel density difference
X-ray =0.156nm
beam spot < 1mm
element Si O C
weight(%) 43.4% 50.6% 6.0%
Si
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Index Scan Study (2)
109mm
109mm
• density relative uniformity
Distance from edge(mm)
Den
sity
rat
io(%
)
edge
center
middle
(n-1)/(n-1) ~ +/-0.02
Index (Fraunhofer method at 405nm) = 1.0577 +/- 0.0006
10.7mmt
need further studies
preliminary value:
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Block Size
• Large sample produced Can be used for real detector 150 x 150 mm2 cross section Thickness: 10 mm and 20 mm
0% 50% 100%
1.045
1.050
1.055
1.060
150x150x20
150x150x10
100x100x10
“crack-free” rate by visual scan
110x110x20mm3 150x150x20mm3
n =1.050
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Machining Possibility
• Hydrophobic feature allows us to use “water-jet” cutter for machining
highly pressurized water injected via very small hole to a sample
hexagonal shape for two samples
110mm150mm
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Multiple-Layer Sample
two-layer sample with 160x160x20 mm3 has been successfully producedone can use two aerogel layers as one unit
n = 1.045
n = 1.050
160mm
transmission length(400nm): 46mm
old new
stress inside a tile well controlled
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High Density Aerogel
• Challenge to produce transparent aerogel with high density index ~ 1.10-1.20 ( ~ 0.4-0.8g/cc ). Fill a “gap” between gas and li
quid. Very difficult to make high density aerogel. Aerogel gets milky and i
t can not be used due to low transparency in a normal way. new method invented
n = 1.22
60x35x10mm3
transmission length: 18mm at 400nm
clear enough to detect Cherenkov photonsNpe ~ 9 for 3 GeV/c pions
RICH2007, Trieste, Italy16
Conclusions
• Aerogel in the 3rd generation has been produced. index : 1.03 - 1.08 transmission length at 400 nm ~ 40 mm clarity factor ~ 0.005-6 m4/cm transparent sufficiently to employ Cherenkov radiator uniformity of index examined with X-ray tomography device
• Various aspects in aerogel production as well as handling possibility have been investigated machining two layer samples with big size of 160x160x20 cm3
• Further attempt for the 4th generation high density aerogels
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KEK - J. Stefan Institute - Univ. Ljubljana - Nagoya - Chiba - Tokyo Metro. Univ. - Toho
Acknowledgements to Matstushita Electric Works
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Backup Slide
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Aerogel Production Procedure
PreparationAging ~2 weeks
Rinse 1Hydrophobic treatment
Rinse 2-1Rinse 2-2
Rinse 2-3(Rinse 2-4)
3 days3 days
2 days2 days
2 days(2 days)
3 daysSupercritical drying
total 1 month