1. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 1 - Use of fiber optic technology for Relative Humidity monitoring in RPC detectors L. BENUSSI 1, S. BIANCO 1, M.A. CAPONERO 1,2, S. COLAFRANCESCHI 1, M. FERRINI 1,3, F. FELLI 1,3, L. PASSAMONTI 1, D. PIERLUIGI 1, A. POLIMADEI 2, A. RUSSO 1, G. SAVIANO 1,3, C. VENDITTOZZI 3 1 Laboratori Nazionali di Frascati dell'INFN 2 Centro Ricerche ENEA Frascati 3 Università di Roma I Presented at RPC2012 by Michele Caponero michele.caponero@enea.it

2. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 2 - Fibre Bragg Grating (FBG) optical sensors: a novel technology that can allow developing distributed monitoring sensing systems for gas-based detectors in large HEP experiments Basic features of FBGs ‘Intrinsic’ optical sensor, directly integrated in the fiber: no power supply at the sensing point. Many sensors can be connected in series on the same optical fiber: reduced cabling. Underlying spectroscopic technique: long term stability for quasi-static measurements; no electro-magnetic disturbances. Hostile environment endurance, Radiation Hardness. Fibre Bragg Grating (FBG): fundamentals Array of n.6 FBGs (strain gauge) FBGs  3mm sheath f.o. (patchcord)  0.9mm sheath (wiring f.o.)

3. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 3 - Fibre Bragg Grating (FBG) sensor: diffraction grating in the core of an optical fiber. Diffraction grating is produced by modulation of the refractive index of the core. FBG Fibre Bragg Grating (FBG): fundamentals

4. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 4 - Probe:  60nm Response:   0.3nm @-3dB Light propagating along the optical fibre is diffracted (back-reflected) by FBGs Response (diffracted) signal Probe signal after diffraction Probe signal before diffraction FBG Many FBGs at different BRAGG can be arranged along one optical fibre Fibre Bragg Grating (FBG): fundamentals

5. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 5 - Diffracted wavelength depends on: -grating pitch affected by Temperature T and Stress  -effective refraction index            Fibre ‘at rest’      Fibre ‘excited’      Fibre Bragg Grating (FBG): fundamentals  = 1    1 pm  T = 0.1  K   1 pm

6. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 6 - Fibre Bragg Grating (FBG) sensor: optical Temperature and Strain Gauge FBG in thermal/structural contact with the component to be monitored FBG sensor FBG signal            FBG signal Fibre Bragg Grating (FBG): fundamentals

7. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 7 - FINUDA FBG sensors already used at INFN – Frascati National Laboratory FINUDA Experiment Monitoring deformations of vertex detector mechanical structure Fibre Bragg Grating (FBG): previous applications for HEP by the INFN-Frascati collaboration

8. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 8 - 11/Dic/2003 -03:08Massive ‘trips’ for some time due to e + injection 10:10DA  NE machine development: Microstrip and Tofino off 16:15Beam stable: Microstip and Tofino on 18:50Microstrip (OSIM1) ‘trip’: recovery procedure 19:15Microstrip stable: take data Microstrip ON Microstrip OFF Massive ‘trips’ of Microstrip Microstrip OFF Microstrip ON Fibre Bragg Grating (FBG): previous applications for HEP by the INFN-Frascati collaboration

9. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 9 - Use of FBG for monitoring RPC gas temperature presented @ TIPP2011 Array of many FBG sensors inserted in gas conduit Monitoring temperature gradient of gas fluxed in RPC detector _______ Early detection and localisation of overheating RPC chambers FBG_1 FBG_n Fibre Bragg Grating (FBG): previous work by the INFN-Frascati collaboration

10. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 10 - gas IN gas OUT FBG Temperature sensor Reference Thermocouple FBG temperature sensor Reference Thermocouple RPCs Fibre Bragg Grating (FBG): previous work by the INFN-Frascati collaboration

11. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 11 - FBG for RH measurement: hygroscopic features of the polyimide recoating FBGs are commercially available with either acrylate or polyimide recoating FBG production procedure 1) Stripping the original coating of the fiber 2) Writing the Bragg grating 3) Recoating

12. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 12 - FBG for RH measurement: hygroscopic features of the polyimide recoating FBGs are commercially available with either acrylate or polyimide recoating Polyimide recoating for RH measurement: swelling due to hygroscopic properties of the polyimide recoating induces stress and modifies the pitch of the Bragg grating Models for polyimide hygroscopic properties are available Hysteresis can be present Hysteresis usually comes from large voids in the polymeric structures and subsequent absorption of water clusters Water clusters can also deform the polymer structure and modify its hygroscopic properties Acrylate (standard fiber cladding) Polyimide (FBG recoating) FBG

13. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 13 - Sensor prototype RH reference measurement by capacitive sensor Temperature measurement for compensation by Thermocouple Polyimide recoated FBG sensor in sealed box to be installed in gas conduit Commercial polyimide recoated FBG sensor TC RH FBG Pipe joint gas inlet Pipe joint gas outlet

14. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 14 - gas IN gas OUT FBG Interrogation System Thermocouple and Hydrometer conditioner RPCs INFN - Frascati National Laboratory Experimental Hall ‘ASTRA’ RPC Test Facility Intended application: monitoring RH of gas fluxed in RPCs Monitoring RH by FBG in RPC detector TC RH FBG

15. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 15 - Sensor prototype testing Preliminary test of sensor prototype in 15% ÷ 60% RU range Test measurement worked out downstream RPC chambers Use of humidifier to control humidity of gas

16. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 16 - Sensor prototype testing RH TT  To work out RH value FBG signal must be conditioned (Temperature compensation) ? ?

17. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 17 - Sensor prototype testing

18. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 18 - Sensor prototype testing

19. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 19 - Sensor prototype testing

20. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 20 - Sensor prototype testing

21. Use of fiber optic technology for Relative Humidity monitoring in RPC detectors- M.A. Caponero @ RPC2012 - 21 - Results show the feasibility of use of commercial polyimide recoated FBG sensors to monitor RH … …but precision and resolution must be improved Planned work to test use of custom recoating on commercial uncoated FBG, either in selected polyimide or other hydroscopic polymer Prospetive: development of custom ‘sensorised gas joint’ Integration with FBG Temperature sensor prototype (previous work), to develop all-in-fiber distributed sensing system for Temperature & RH Conclusions and Future Work RPC gas flow optical fiber FBG embedded in custom gas joint FBG fiber pigtails and connector