Study of oat glass as electrode for RPC

Transcription

1 Study of oat glass as electrode for RPC K. Raveendrababu*, P. K. Behera Physics Department, IITM, Chennai-36, INDIA. B. Satyanarayana DHEP, TIFR, Mumbai-05, INDIA. S. Mukhopadhyay, N. Majumdar ANP Division, SINP, Kolkata-64, INDIA. DAE Symp-2014, 09/11, IITG K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 1 / 21

2 Outline 1 Introduction 2 Scanning Electron Microscope (SEM) Analysis SEM Images Elemental composition 3 Density measurements 4 Relative Permittivity 5 Ageing issues of glass RPCs Plasma chemistry involved in glass RPCs operation Surface prole studies of glass samples Brand new glass sample studies Eect of HF on glass surfaces 6 Conclusions 7 Acknowledgements K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 2 / 21

3 Introduction (1) Introduction Resistive Plate Chamber (RPC). The layout of three modular INO-ICAL detector. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 3 / 21

4 Introduction Continued... Scope of the work The active elements in INO-ICAL detector are RPCs of 2m x 2m area. The number of RPCs will be used in INO-ICAL detector are 28,800. Hence there is a need of rigorous studies on the glass samples for the better selection of RPC electrodes. We have done a detailed characterization studies on glass samples from various manufacturers, viz. Asahi, Italian, Japanese and Saint-Gobain. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 4 / 21

5 Scanning Electron Microscope (SEM) Analysis SEM Images (2.1) SEM Images We scanned both sides of the four glass samples using FEI Quanta 200 Scanning Electron Microscope. ASAHI SIDE-1 ITALIAN SIDE-1 JAPANESE SIDE-1 SAINT-GOBAIN SIDE-1 ASAHI SIDE-2 ITALIAN SIDE-2 JAPANESE SIDE-2 SAINT-GOBAIN SIDE-2 K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 5 / 21

6 Scanning Electron Microscope (SEM) Analysis Elemental composition (2.2) Elemental Composition The various elemental composition of the glass samples were obtained from the Energy Dispersive X-ray Spectroscopy (EDAX) technique using FEI Quanta 200 Scanning Electron Microscope. There is no signicant variation in composition among the glass samples. Element Asahi (At%) Italian (At%) Side1 Side2 Side1 Side2 Oxygen (O) Sodium (Na) Magnesium (Mg) Silicon (Si) Calcium (Ca) Iron (Fe) Element Japanese(At%) Saint-Gobain(At%) Side1 Side2 Side1 Side2 Oxygen (O) Sodium (Na) Magnesium (Mg) Silicon (Si) Calcium (Ca) Iron (Fe) Summary of the various elemental composition in atomic level (At%) of the glass samples from dierent manufacturers. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 6 / 21

7 Density measurements (3) Density of glass samples Experimental technique The density measurements of the glass samples were measured using the METTLER-AE163 laboratory weighing balance, which works on the Archimedes buoyancy principle. We used pure water as reference uid. The density of immersed object relative to the density of uid could be calculated using : Volume of the sunken object = Volume of the displaced uid = ϱ = W 1 W 2 ϱ 0 Here W 1 = Weight of object in air, W 2 = (Weight of object in air - Apparent weight of object in water), and ϱ 0 = density of water at 27.4 C( room temperature) = g/cc. The average density of Italian glass sample is about 66% of the average densities of other three, which are having identical densities. Hence we would expect that comparatively the RPCs made of Italian glass would be less in weight. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 7 / 21

8 Density measurements Continued... Asahi Glass Italian Glass Sample No. W1 W2 Density Sample No. W1 W2 Density (g/cc) (g/cc) Asahi Italian Asahi Italian Asahi Italian Asahi Average Average Japanese Glass Saint-Gobain Glass Sample No. W1 W2 Density Sample No. W1 W2 Density (g/cc) (g/cc) Japanese SG Japanese SG Japanese SG Japanese SG Average Average Summary of the density of glass samples from the dierent manufacturers. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 8 / 21

9 Relative Permittivity (4) Relative Permittivity Denition : ɛ r = ɛ ɛ 0. Here ɛ is the permittivity of material and ɛ 0 is the permittivity of free space. 1 The relaxation time of electrode τ = RC and C = ɛ r C vac. Here R is electrode's bulk resistivity, C is capacitance, ɛ r is relative permittivity. For high rate RPCs lower the electrode's relaxation time, higher will be the detector's counting rate. 2 Resistive electrode stored energy is W = 1 2 R D. Edv. Here D = ɛ E. The permittivity should be kept as small as possible for the case of high rate RPCs to protect the front end readouts, from electrode's storage energy, by compensating with ampliers with great gain. 3 For properly designed RPC, the requirement is that, most of the voltage should be dropped into the gas gap. Continuity of the electric eld displacement at the plate/ gas interface states that D = ɛ g E g = ɛ p E p. Hence, the bigger the inequality of ɛ p > ɛ g, the higher the voltage drop in the gap. For INO-ICAL detector, the choice of higher permittivity electrode is better since we can operate the RPCs (28,800 in number) in a lower bias voltage and also it is a low counting rate detector. Reference: Conductivity and charge depletion aging of resistive electrodes for high rate RPCs; K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 9 / 21

10 Relative Permittivity Continued... The relative permittivity was measured using "novocontrol Technologies Broadband Dielectric/ Impedance Spectrometer". Saint-Gobain glass would be a better electrode for high count rate RPCs. Italian glass would be a better choice for low count rate RPCs (For example, for the INO-ICAL detector). Relative Permittivity Italian Asahi Japanese Saint-Gobain Frequency (Hz) Relative Permittivity K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 10 / 21

11 Ageing issues of glass RPCs Plasma chemistry involved in glass RPCs operation (5.1) Plasma chemistry involved in glass RPCs operation Gas mixture used for INO glass RPCs operation The optimized gas mixture for glass RPCs operation in Avalanche mode is: 1 R134a (C C 2H 2F 4 or Freon) : 95.2% (Acts as target for energetic particles to ionize.) 2 Iso-butane (i i C 4H 10) : 4.5% (To quench photons produced in the avalanche.) 3 SF 6 : 0.3% (To quench secondary electrons, which create streamers.) Though we might use dry R134a gas in RPC operation, the uorine component of R134a could react with traces of water vapor present in the gas system loop and produce Hydrogen Fluoride (HF). References: (1) H. Sakai et al., Study of the eect of water vapor on a resistive plate chamber with glass electrodes, Nucl. Instr. Meth. A 484 (2002) (2) T. Kubo et al., Study of the eect of water vapor on a glass RPC with and without freon, Nucl. Instr. Meth. A 508 (2003) This (HF) is an aggressive acid to the oat glass, hence plays a major role in damaging the inner surfaces of the glass electrodes and there by reduces the life time of RPC. Reference: Changguo Lu, RPC electrode material study, Nucl. Instr. Meth. A 602 (2009) K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 11 / 21

12 Ageing issues of glass RPCs Plasma chemistry involved in glass RPCs operation Continued... Expected chemical reactions of 'HF' with oat glass SiO 2 + 4HF SiF 4 + 2H 2O (SiF 4 is gas and hence may escape from the detector volume with gas ow, if it is enough). Reference: BOOKHEIM A., J. CHEM. EDUC., 13, 93 (1936). SiF 4 + 2F SiF 2 6 (May deposit on anode). Na 2O + 2HF 2NaF (salt) + H 2O (Might happen on both anode and cathode). CaO + 2HF CaF 2(salt) + H 2O (Might happen on both anode and cathode). Due to the above chemical reactions the inner surface of glass electrodes of RPC might become rough, during its long term run. This might cause the eld emission of electrons from cathode surface and hence there by deteriorating the RPC performance. Reference: Changguo Lu, RPC electrode material study, Nucl. Instr. Meth. A 602 (2009) K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 12 / 21

13 Ageing issues of glass RPCs Plasma chemistry involved in glass RPCs operation Continued... Polymerization In the avalanche, (C C 2H 2F 4) and (i i C 4H 10) would produce the radical, like CH 2 :, is a precursor for the production of polyethylene (C 2H 4)nH 2, an excellent insulator, there by could lead to the Malter eect. Polymerization Malter eect Courtesy : Mar Capeans; Overview of Radiation Hardness of Gaseous Detectors@IPNO, Orsay, June 25-26, K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 13 / 21

14 Ageing issues of glass RPCs Surface prole studies of glass samples (5.2) Surface roughness studies Experimental technique The surface roughness of the brand new samples was measured with "BRUKER ContourGT Optical Microscope". Resolution of the instrument is < 0.01nm. Reference: DS552-RevA0-ContourGTK 3D-Optical Microscope Datasheet.pdf The RMS roughness (Rq) of the surface can be dened as the standard deviation of the elevation, z values, within the given area is calculated from R q = q P(zi z ave ) 2 Here 'z ave' is the average of the 'z' values within the given area, 'z i ' is the 'z' value for a given point, and 'N' is the number of points within the given area. N K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 14 / 21

15 Ageing issues of glass RPCs Surface prole studies of glass samples (5.2.1) Surface roughness of brand new glass samples The size of each scan is 400 µm x 500 µm. The Japanese and Saint-Gobain samples are smoother compared to the other two. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 15 / 21

16 Ageing issues of glass RPCs Surface prole studies of glass samples Continued... K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 16 / 21

17 Ageing issues of glass RPCs Surface prole studies of glass samples (5.2.2) Eect of HF on smoother surface of glass samples 48% Hydrouoric acid (HF) was applied on the smoother surface of each of the glass sample and left for dry, and then we kept the samples in vacuum for 76 hours so that there won't be deposits of water vapor on them, which may add up to the actual surface roughness. The HF applied glass samples surface roughness was measured using "LEXT 3D Measuring Laser Microscope OLS4000". Resolution of the instrument is 0.01µm. The size of each scan is 646 µm x 647 µm. We found that Saint-Gobain glass sample is less eected by applied HF. ASAHI; Sq = 2.174µm ITALIAN; Sq = 1.992µm K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 17 / 21

18 Ageing issues of glass RPCs Surface prole studies of glass samples Continued... JAPANESE; Sq = 2.336µm SAINT-GOBAIN; Sq = 1.754µm Confocal Microscope images after applying HF. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 18 / 21

19 Conclusions (6) Conclusions There is no signicant variation in elemental composition among the four glass samples from dierent manufacturers. We found that the average density of Italian glass sample is about 66% of the average densities of other three, which are having identical densities. Hence we would expect that RPCs made of Italian glass are less in weight. From relative permittivity studies, it was found that electrode made of Saint-Gobain glass would be a better choice for high count rate RPCs and that of Italian glass for low count rate RPCs (For example, for the INO-ICAL detector). Japanese and Saint-Gobian glasse samples are comparatively smoother. It was observed that Saint-Gobain glass sample is less eected by applied HF than the other three samples. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 19 / 21

20 Acknowledgements (7) Acknowledgements This work was supported by the Department of Atomic Energy (DAE) and Department of Science and Technology (DST), Government of INDIA. The authors would thank to the Chemistry, Metallurgy and Electrical Engineering departments of IITM, Chennai, for allowing to use the needed instruments for this work. K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 20 / 21

21 Acknowledgements Thank You K. Raveendrababu () Study of oat glass as electrode for RPC DAE Symp-2014, 09/11, IITG 21 / 21