towards sealed gem-based flame detectorsconclusions • gem approach offers the possibility to...
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Towards sealed GEM-based flame detectors
G. De Cataldo1,2, G. Volpe1,2, V.Peskov1,2,3
1CERN
2Bari University
3Inst for Chem.Phys., RAS
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In fire safety it is very important to record appearance of a flame
on its early stage
EU standard:The highest sensitivityClass 1: ~30x30x30cm3 flame on ~20m in 20sec
There are various commercial flame detectors on the market
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An example of the Class-1 detector
It is a digital device, it cannot distinguish between a single photon and a spark
Hamamatsu UVtronis used in some sensors produced by other companies
UV light from flamesCreate photoelectronsfrom the metal cathodeand they trigger a glow discharge. The latter isquenched by an externalresistor
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Ours idea-CsI coating to enhance the QE
.. the spin of ALICE and COMPASSapproach for Cherenkov photons detection
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Laboratory prototype
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First sealed detector (industrial prototype)
The detector showed stable operation for 12 years, The sensitivity was 100 times higher than Hamamatsu(the QE loss was due to the exposure to air). The detector was demonstrated in operation at CERN open days
The history of manufacturing:
Miranda evaporated theCsI photocathode at CERN ona inner surface of the tube.
It was put then to a plastic bag and sent to Oxford Instr., wherethe detector was filled with the gas and sealed
CsI was exposed to air for one week
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Immediate gain in sensitivity 1000 times
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It is excellent for indoor applications, however in direct sunlight ”noise” pulses appear
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Alternative approach
-photosensitive vapour. In this case the sensitivity to direct sunlight is practically zero
Ethylferrocene
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TMAE
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Efficiency vs. temperature
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Detectors with photosensitive gases are efficient at room and elevated temperatures
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Signals from invisible sparks
All these detectors were exploitedin proportional mode,so they can distinguish betweensingle photons and sparks
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This why we are consideringnow a GEM-based approach
It offers several advantages, for example:
Compact flat-panel geometry
Large area-herefore, higher sensitivity
Single wire detectors: in the past the cost of sealed X-ray counter was low, around 100 Euro,(Hamamatsu is around 50 Euro), including HV supply and electronics.
However, nowadays they are not produced anymore (solid state detectors took over)To start their production is not easy and require a considerable investment
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We started of course, with flushed detectors (this part of work was done in collaboration with A. Di Mauro and P. Martinenego and was supported by the CERN Technology Transfer office )
In this work we try to learn the difficulties in this approach
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Examples of optimizations made in flush mode:
choice grift region geometry
Choice of THGEM and RETGEM geometries: t=0.8, d=0.6, s=1,h=0.1mmand
t=0.4, d=0.5, s=0.9,h=0.1mm
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Example of some results:efficiency vs radius
Conclusion : there ae some losses, but the construction is simpler
Break due to windows geometry
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In principle, one can gain sensitivity further with the window size increase
From:Di Mauro, P. Martinego, V. PeskovReport to CERNTech. Transfer office
Comparison with Hamamatsu
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Sealed detectors
In the case of CsI thedrift was 10 mmIn the case of photosensitive gases it was 80 mm
Teflon pieces were changed to ceramics
In first experiments we used heating tapes wrapped in Al foil 150-180, pumped for7-10 days, the vacuum was better 10-6 Torr
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Later a more advanced, more convenient, setup was developed
Heating cabinet(in collaboration with A. Di Mauro)
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Vacuum, 1 cm
CsI, 1 cm, Ne+5%CH4
TMAE, 80mm Ne+5%CH4
EF, 80mm, Ne+5%CH4
Ionization chamber measurements
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Voltage (V)
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Ne as a cleanness probeCurrent measurements
Double THGEMt=0.4, d=0.5, s=0.9,h=0.1mm
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In TMAE THGEMs become noisy even if we introduce its vapours
below the saturation value
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Original idea expressed in CERN PatentApplication.Authors:R. Oliveira, Di Mauro, P. Breule, V. Peskov
Oxide Cu (0.2 mm thick)
Ceramic
First prototypes were developed byelectronic Workshop in Ecole des Mine,
St. Etienne, France
Latest prototype-Ragent-(a photonic branch of theInst. for Chem. Phys. RAS)
Later a similar detector was developed and successfully tested by the Inst of Nucl. Phys. RAS
0.4 mm
Hols 0.4mm
Special THGEM design for TMAE(to avoid leakage current)
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Gain and stability in other gases
The method:Stabilization at low gain and step by step increase
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Note: adding a sun-blocking filter reduce the efficiency of the CsI THGEM four times
Comparison sealed GEM-based detectors with Hamamatsu
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In contrast to Hamamatsu GEM-based detectors are capable to detect sparks
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Stability with temperature
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However, the necessity to use filters create some problems,e.g:
size,price
The most attractive are GEM-based detectors with CsI photocathodes:
they operate stably in wide temperature interval
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Pilot studies progress:CsI surface coating as an incorporated filter
(in collaboration with Di Mauro, P. Martinengo and P. Breul)
CERN Techn.Transfer office filed a patent application
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Conclusions
• GEM approach offers the possibility to manufacture compact ,but large area, high sensitivity flame detectors
• CsI detectors the most attractive , but require filters for outdoor applications
This increase the cost
• GEMs with photosensive vapours practically are not sensitive to the direct Sunlight, but have high QE only at temperatures more than 15C. So they are good either for indoor application or for outdoor applications in warm countries (Greece, Israel, Italy, California etc)
• It will be attractive to coat CsI with a incorporated filter
Our nears effort will be focused on optimization of these layers
• We are also working on imaging version of GEM-based flame detectors
Probably we will be able to present some results on one of the RD51 meetings
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Backup
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