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

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

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

Ours idea-CsI coating to enhance the QE

.. the spin of ALICE and COMPASSapproach for Cherenkov photons detection

Laboratory prototype

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

Immediate gain in sensitivity 1000 times

It is excellent for indoor applications, however in direct sunlight ”noise” pulses appear

Alternative approach

-photosensitive vapour. In this case the sensitivity to direct sunlight is practically zero

Ethylferrocene

TMAE

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Efficiency vs. temperature

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Detectors with photosensitive gases are efficient at room and elevated temperatures

Signals from invisible sparks

All these detectors were exploitedin proportional mode,so they can distinguish betweensingle photons and sparks

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

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

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

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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Series1 Series2 Series3

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

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

Later a more advanced, more convenient, setup was developed

Heating cabinet(in collaboration with A. Di Mauro)

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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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

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)

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

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

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

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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