Improving count rate capability of timing RPCs by increasing the detector working temperature

Improving count rate capability of timing RPCs by increasing the detector working temperature PM2021, 15th Pisa Meeting on Advanced Detectors, edition 2020 22–28 May 2022 La Biodola - Isola d'Elba (Italy) A. Blanco1, P. Fonte1,2, L. Lopes1 J. Saraiva1 1 Laboratory of Instrumentation and Experimental Particles Physics, Coimbra, Portugal 2 Coimbra Polytechnic - ISEC, Coimbra, Portugal Abstract -This communication describes test beam results, focusing on detection efficiency and timing precision, of common float glass timing Resistive Plate Chambers (tRPCs) exposed to a 2.7 GeV proton beam and operated at higher operational temperature in order to increase the count rate capability of the chambers, by exploiting the reduction in the resistivity of the glass electrode, one of the limiting factors. Results suggest that the count rate capability can be extended at least up to 1500 Hz/cm2 when the detector is operated at 40.6 ºC without noticeable loss of efficiency or timing precision degradation with values of 90 % and 100 ps, respectively, for this specific timing RPC chamber arrangement. tRPC have traditionally been used with relatively low particle flux (< kHz/cm2) due to the inherent limitation to the counting rate imposed by the commonly used float glass electrode resistivity. Since tRPCs are one of the main large-area timing detectors, extension of its counting rate capability is of great interest for future High Energy Particle (HEP) experiments, were the luminosity is expected to increase considerably. Attempts have already been made to increase the count rate capability by using materials with lower electrical resistivity compared to the commonly used float glass, such as ceramics [1], [2], special glasses [3] or some technical plastics [4]. As a result, the operation of small area detectors was successfully achieved, but the implementation of the medium/large area detectors failed due to the lack of homogeneity of the materials, which present spurious low electrical resistivity paths, resulting in an unstable behavior of the detector. Another possibility, still very little explored, is to decrease the resistivity of standard float glass by increasing the operational temperature of the detectors, providing a ten-fold decrease in resistivity every 25 ºC. ϕ max≤ΔV ρ d¯ q 1 - INTRODUCTION Φmax = maximum particulate flux ΔV = allowable voltage drop at the resistive electrode, which does not compromise performance. ρ = electrode resistivity d = electrode thickness q = average charge per avalanche Φmax can be increased by decreasing ρ ρ can be decreased by increasing temperature factor 10 every 25 ºC [1] L. Lopes et al. “Accurate timing of gamma rays with high-rate Resistive Plate Chambers”. NIMA 573.1 (2007).pp. 4–7. [2] L. Naumann et al. “Ceramics high rate timing RPC”. NIMA 628.1 (2011). pp. 138–141. [3] Jingbo Wang et al. “Development of multi-gap resistive plate chambers with low-resistive silicate glass electrodes for operation at high particle fluxes and large transported charges”. NIMA 621.1 (2010), pp. 151–156. [4] D. Belver et al. “The HADES RPC inner TOF wall”. NIMA 602.3 (2009). pp. 687–690. [5] D. Belver et al. “Performance of the Low-Jitter High-Gain/Bandwidth Front-End Electronics of the HADES tRPC Wall”. IEEE Transactions on Nuclear Science 57.5 (Oct. 2010), pp. 2848–2856. [6] A Neiser et al. “TRB3: a 264 channel high precision TDC platform and its applications”. JINST 8.12 2013, pp. C12043–C12043. 2 – EXPERIMENTAL SETUP AND METHODS R P C 4 R P C 3 R P C 2 R P C 1 sc1 sc2 sc3 a) b) c) d) e) 1 3 1 2 4 2 3 1 1 2 RPC4 RPC3 RPC2 RPC 1 1 mm 1 mm 2 mm 2 mm Beam Line Figure 1. a). Internal arrangement of the tRPC chambers. b) Cross section of the four chambers arrangement. c) RPC chamber: 1 aluminum and 2 glass electrodes, 3 plastic support bar, 4 aluminum tube. d) Panoramic view of the setup in the beam line, showing the tRPC chambers gas box, surrounded by the heating wire, and the last scintillator of the telescope. e) Cross section of the scintillator and tRPC counters in the beam line. ●Four Individually shielded strip-like tRPC chambers [4], 750 mm long, widths of 22 and 44 mm and glasses of thickness 1 mm (~4.1012 Ωcm) and 2 mm (~1.1013 Ωcm) with 0.270 mm gap width. ●Gas box with controlled temperature. ●Scintillator telescope as time reference. ●Both tRPC and the PMTs signals are fed to a fast FEE [5] read out by the TRB board [6] equipped with 128 multi-hit TDC (TDCin-FPGA technology) channels with a time precision better than 20 ps. ●The chambers were operated in open gas loop with a mixture of 97% C2H2F4 and 3% SF6 and exposed to 2.7 GeV protons. R P C 4 1 m m R P C 3 1 m m R P C 2 2 m m R P C 1 2 m m s c 1 s c 2 s c 3 ???? Request hits in the scintillators and check the RPC Efficiency determination Beam line R P C 4 1 m m R P C 3 1 m m R P C 2 2 m m R P C 1 2 m m s c 1 s c 2 s c 3 ( 1 1 0 1 0 1 0 1 1 ) ( σ(RPC)2 σ(SC 1)2 σ(SC 2)2 ) = ( σ(Δ(RPCSC 1))² σ(Δ( RPCSC 2))² σ(Δ(SC 1SC 2))² ) Timing precision determination Compare RPC with scintillators 30 ps σ Time from RPC and scintillators are corrected by charge. Walk correction. This work was supported by Fundação para a Ciência e Tecnologia, Portugal, in the framework of the project CERN/FIS-INS/0009/2019 and by the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement AIDAinnova – No 101004761. Efficiency and timing precision as a function of the incident particle flux density at a working temperature of 21 ºC and reduced electric field of 443 Td. It is observed that the tRPCs with 2 mm glass (RPC2 and RPC1) lose efficiency much faster and have a worse timing precision. This difference is due to two factors. On the one hand the thickness of the glass and on the other hand the resistivity itself which is 2 - 3 times lower in the 1 mm glass, giving in combination a factor of 4 - 6 in resistance. 0 200 400 600 800 1000 1200 1400 1600 Rate (Hz/cm²) 0 25 50 75 100 Efficiency (%) rpc1 rpc2 rpc3 rpc4 polynomial fit 0 200 400 600 800 1000 1200 1400 1600 Rate (Hz/cm²) 0 50 100 150 200 Time precision (ps) 0 200 400 600 800 1000 1200 1400 1600 Rate (Hz/cm²) 0 25 50 75 100 Efficiency (%) 21 ºC (443 Td) 30.5 ºC (415 Td) 40.6 ºC (414 Td) polynomial fit 0 200 400 600 800 1000 1200 1400 1600 Rate (Hz/cm²) 0 50 100 150 200 Time precision (ps) 0 200 400 600 800 1000 1200 1400 1600 Rate (Hz/cm²) 0 25 50 75 100 Efficiency (%) 21 ºC (443 Td) 30.5 ºC (415 Td) 40.6 ºC (414 Td) polynomial fit 0 200 400 600 800 1000 1200 1400 1600 Rate (Hz/cm²) 0 50 100 150 200 Time precision (ps) 3 – RESULTS Efficiency and timing precision for RPC2 (2 mm thick glass) and RPC3 (1 mm thick glass) chambers as a function of the incident particle flux for three different working temperatures 21 ºC, 30.5 ºC and 40.6 ºC. The efficiency recovery, with increasing operating temperature (due to decreasing resistivity), is evident, becoming basically independent of the incident particle flux (at least up to 1500 Hz/cm2) for a temperature of 40.6 ºC for RPC3 . The improvement for RPC2 is smaller due to the higher resistance of the glass. Time precision for the same conditions mentioned for efficiency. Again, the recovery in timing precision is observed as the operating temperature increases, remaining at a level of approximately 100 ps up to 1500 Hz/cm2 for RPC3. We have shown that increasing the working temperature of a tRPC can substantially improve its counting rate capability. In particular, individually shielded strip-like tRPC chambers with an active area of 750 x 44 mm equipped with 4 gaps of 0.270 mm, show the same efficiency, 90 %, and approximately the same timing precision, 100 ps, over a range of incident particle fluxes up to 1500 Hz/cm2 when their working temperature is raised to 40.6 ºC. This contrasts with a 20 % loss of efficiency and a worsening of temporal precision of more than 60 ps when operated at 21 ºC. 4 – CONCLUSIONS Beam line RPC1,2 2 mm glass thickness RPC3,4 1 mm glass thickness