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SiO x coated fiber optic sensor for gas monitoring in RPC

This project focuses on the development of an innovative sensor for gas monitoring in Resistive Plate Chambers (RPCs), a type of fast gaseous detector used in particle physics experiments. The sensor, based on SiOx coated plastic optic fiber, offers high detection capabilities and is immune to electrostatic discharges and magnetic fields. It provides a cost-effective and reliable solution for monitoring gas concentrations in RPCs.

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SiO x coated fiber optic sensor for gas monitoring in RPC

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  1. SiOx coated fiber optic sensor for gas monitoring in RPC S. Grassini1, M. Parvis2, M. Ishaiwi2 1 Dip. di ScienzaApplicata e Tecnologia2Dip. di Elettronica e Telecomunicazioni, Politecnico di Torino, Italy L. Benussi, S. Bianco, S. Colafranceschi, D. Piccolo INFN- Istituto Nazionale di Fisica Nucleare, Frascati, Italy

  2. Project supported by ItalianResearchMinistery PRIN2008 Innovative sensors for gas monitoring • Politecnico di Torino • Università di Roma la Sapienza • INFN- Istituto Nazionale di Fisica Nucleare, Frascati

  3. The Higgs Boson Hunt

  4. RPC: Resistive Plate Chambers Fast gaseous detectors that provide a muon trigger system µ+ Detecting strips Bakelite plates (= 2-5x1010 Ω∙cm) V = 9.0 kV GAS GAP 2 mm HV Al foil Gas mixture: 96% of C2H2F4 / 3.5% of iC4H10 / 0.5% SF6 ; 45% RH

  5. RPC issue • It is known that an increase of the leakage current with time is observed, which may impair the muon detection • The chemical analysis showed a correlation between leakage current increase and F-concentration in the gas • The F-concentration can be reduced by renewing the gas, but the gas mixture is expensive and the volumes are huge so that a closed loop recirculation system with gas filters was designed • New gas fraction variable from 30% (currently) to 2%

  6. The RPC Closed-loop system RPC RPC Chemical analyses (GC, ICP-MS)

  7. New proposed approach RPC RPC Plastic Optic Fiber Sensor

  8. POF sensor • immune to electrostatic discharges and magnetic fields • fire safety compliance • robust and flexible • cheap • easy to obtain high detection capabilities via cumulative output responses

  9. Plastic Optic Fiber Sensor LED PD • Claddingremoval (in ethylacetate) • Depositionon the core of a sensitive layer capable of reacting with the gas • Selective and non-reversible Sensor principle The chemical reaction must alter the fiber light transmittance capability

  10. Radiation effect @ the Gamma IrradiationFacility (GIF) - CERN • A very intense (740 GBq) 137Cs source • A continuous photon load • Six months test exposing the fiber to 2 Gy (corresponding to several months of CMS operation) No light transmittance changes detected both on bare and coated fibers

  11. Sensitive Layer deposition via plasma Glow discharge

  12. Sensitive Layer deposition via plasma • Ag layer by plasma sputtering • SiOx by PECVD of organosilicon compounds Glowdischarge

  13. CO CO2 H(OH)C H2O, OH Si(CHx)y O2, O CHX OSi(CHX)Y CH + H (CH3)2C H Si SiO C2H2 CH4 CH3 OH CH2 OH O O Si Si Si Si Si O OH O O H O CH2 OH O O Si Si Si Si O O O O Si Si CH2 O SiOx layer (a glass-like layer) TEOS + Ar + O2 SiC8H20O4 Electron bombardment Ion bombardment

  14. SiOx layer (a glass-like layer) The SiOxhas an high reflectiveindexwhichmakes the fiber dispersive The F-reacts with SiOxcorroding the layer: SiO2 + 4 HF  SiF4 + 2 H2O TEOS:O2:Ar plasma @ 5 Pa - 50  100 W 200 nm

  15. Measuring set-up POF SENSORS PT100 HF solution REACTION CHAMBER

  16. HF vapor exposition PHF200 Pa The current increases as the time passes until a plateau

  17. HF effect on the fiber dispersion Uncoated fiber SiOx coated SiOx coated + HF

  18. HF effect on the fiber surface before 50 µm 1 µm

  19. HF effect on the fiber surface before after 50 µm 50 µm 1 µm 1 µm

  20. Plasma chemistry and fiber response to HF TEOS:O2: Ar=1:20:10 100W TEOS:O2: Ar=1:0:30 50W

  21. Plasma chemistry and fiber response to HF TEOS:O2: Ar=1:20:10 100W TEOS:O2: Ar=1:0:30 50W 1 µm

  22. Plasma chemistry and fiber response to HF TEOS:O2: Ar=1:20:10 100W TEOS:O2: Ar=1:0:30 50W 1 µm 1 µm

  23. Plasma chemistry and fiber response The FTIR shows the presence of organic groups which make the coating not completely glass-like

  24. Plasma chemistry and fiber response Increasing O2 a fraction and discharge power leads to SiO2-like films The sensitivity significantly increases

  25. Conclusions • Plasma modified POFs can be successfully used for measurement of F-concentration in gas mixtures • The sensors are cumulative so theydirectly estimate the filterexposition • First prototypes showed a good sensitivity (the light changes 3 times after an exposition of 15000 ppm per hour) • The overall sensor cost is less than 1€ • Experiments are being performed to assess the sensor repeatability

  26. Thank you CMS building – CERN - February 2011

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