A new kind of particle detector based on RPC-like structure was developed. Semi-conductive electrodes with resistivity ρ up to 108 Ω·cm have been used to improve the RPC rate capability. The aim is to obtain a detector with

sub-nanosecond time resolution capable of working in a high-rate environment (rate capability of the order of MHz/cm2). In this paper the results on two different detector structures are presented: one with 1 mm gas gap and both SI(Semi-Insulating)- GaAs electrodes (ρ ∼ 108 Ω·cm), and the other characterized by 1.5 mm gas gap,

one SI-GaAs electrode and one intrinsic silicon electrode (ρ ∼ 104 Ω · cm)

Bruno, S.

Caltabiano, A.

Camarri, P.

Cardarelli, R.

Liberti, B.

Pizzimento, L.

Rocchi, A.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2018-18100-2Communications: SIF Congress 2017IL NUOVO CIMENTO 41 C (2018) 100Development of gaseous particle detectors based onsemi-conductive electrode platesA. Rocchi(1) on behalf of R. Cardarelli(2), B. Liberti(2), P. Camarri(1),A. Caltabiano(1), S. Bruno(1) and L. Pizzimento(1)(1) Universitá di Roma Tor Vergata - Via della ricerca scientifica 1, Roma 00133, Italy(2) INFN Sezione Tor Vergata - Via della ricerca scientifica 1, Roma 00133, Italyreceived 30 January 2018Summary. — A new kind of particle detector based on RPC-like structure wasdeveloped. Semi-conductive electrodes with resistivity ρ up to 108 Ω·cm have beenused to improve the RPC rate capability. The aim is to obtain a detector withsub-nanosecond time resolution capable of working in a high-rate environment (ratecapability of the order of MHz/cm2). In this paper the results on two different detec-tor structures are presented: one with 1 mm gas gap and both SI(Semi-Insulating)-GaAs electrodes (ρ ∼ 108 Ω·cm), and the other characterized by 1.5 mm gas gap,one SI-GaAs electrode and one intrinsic silicon electrode (ρ ∼ 104 Ω · cm).1. – IntroductionThe increasing luminosity in future colliders requires the development of new detec-tors capable of working with higher rate and higher time resolution for bunch crossingidentification. At present, the rate capability of RPCs (Resistive Palte Chambers) ex-ceeds 1 kHz/cm2 [1]. Due to the detector ageing, the initial rate capability drops off asthe integrated luminosity increases. The RPC detectors developed for the experimentsat LHC (designed luminosity L = 1014 cm−2 s−1) can work for ten years at a rate of100 Hz/cm2 [1]. At future colliders such as HL-LHC and FCC (Future Circular Collider)the luminosity will increase by a factor of 5 to 30 [2]. In this scenario it would be ex-tremely useful to develop a detector similar to the RPC as far as time resolution andradiation hardness are concerned, but with a rate capability of the order of MHz/cm2.2. – Increasing the rate capabilityAn RPC [3,4] detector can be described as a set of unit cells interconnected accordingto the diagram in fig. 1. A unit cell is characterized by the gas capacitance CG, theelectrodes capacitances C and by RT and RL resistances, which represent respectivelyCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 A. ROCCHI et al.Fig. 1. – Semplified equivalent circuit superimposed on an RPC detector sketch.the electrode resistance in the normal and parallel directions with respect to the electrodesurface. RG is the resistance of the graphite layer which distributes the high voltage Von the electrode surface.If the high voltage across the gas gap Vgas is high enough (applied electic field Egreater than 5 kV/mm for 95%/4.5%/0.5% of C2H2F4-iC4H10-SF6 gas mixture), a ion-izing particle crossing a unit cell triggers an avalanche multiplication. This process canbe seen as the closure of the switch in the equivalent circuit of the unit cell involved inthe discharge. The resistance RT dumps the voltage across the gas gap proportionally tothe current generated in the avalanche discharge. The resistance RL  RG restricts thetransfer of energy from adjacent cells, and this is the reason for the RPC rate capability.When a charged-particle flux Φ crosses an RPC detector, the simultaneous ignition ofmany unit cells occurs and the cumulative effect causes a voltage drop on the electrodes.Expressing the electrode resistance as a function of the electrode resistivity ρ and thethickness d, as shown in fig. 2, the effective voltage on the gas gap can be written as ineq. (1) with 〈Q〉 representing the mean charge involved in a single process and Φeff thenumber of processes occurring in the detector per unit time and surface.(1) Vgas = V − 2ρd〈Q〉Φeff .Fig. 2. – Representation of a three-dimensional electrode unit cell.DEVELOPMENT OF GASEOUS PARTICLE DETECTORS ETC. 3Fig. 3. – Prototype sketch.The effective flux Φeff contains the contribution of both the spontaneous noise andthe ionizing-particles events, the latter being a fraction εΦ of the particle flux, where εis the efficiency and it depends on the voltage across the gas gap Vgas. For ε ∼ 1 and Φmuch greater then the noise flux, then Φeff ∼ Φ. To prevent the detector from losingefficiency as Φ rises, it is necessary to minimize the voltage drop on the electrodes insuch a way to fix the Vgas value. For this purpose two strategies have been combinedduring the test:• reduction of the average charge 〈Q〉 using a charge amplifier with high signal-to-noise ratio [5];• replacement of the standard insulating electrodes with Semi-Insulating electrodeswith lower resistivity ρ and thickness d.3. – PrototypesThe first tested prototype was made of two SI-GaAs electrodes spaced with a 1 mmthick PET circular crown. Both electrodes were 400 μm thick and had a resistivity ofthe order of 108 Ω · cm. The gas gap was filled with a gas mixture of C2H2F4-iC4H10-SF6 (95%/4.5%/0.5%). The signal was read with a pad placed under the low-voltageelectrode (see fig. 3).The second prototype had 1.5 mm gas gap, one silicon electrode and one SI-GaAselectrode. In this case the gas gap was filled with a gas mixture of iC4H10-Ar (60%/40%).Both detectors were placed in series with a 100 MΩ resistance in order to avoid thatthe power dissipated in the electrode due to any anomalous electric discharge may damagethe crystal. The operational parameters of the charge amplifier used for the FE electronicare listed in table I.Table I. – Front End electronics features.Voltage supply 3–5 VSensitivity 2–4 mV/fCNoise (up to 20 pF input capacitance) 1000 e− RMSInput impedance 100–50OhmB.W. 10–100 MHzPower consumption 10 mW/chRadiation hardness 1Mrad, 1013 n · cm−24 A. ROCCHI et al.(a) (b)(c)Fig. 4. – (a) Time difference with respect to the trigger detector [6] corrected for the time-walk effect (HV = 5630V, prototype 1); (b) “efficiency times acceptance” (1 mm gas gap,prototype 1); (c) Pulse samples, prototype 1.(a) (b)(c)Fig. 5. – (a) Time difference with respect to the trigger detector corrected for the time-walkeffect (prototipe 2); (b) “efficiency times acceptance” (1.5 mm gas gap, prototype 2); (c) Pulsesamples, prototype 2.DEVELOPMENT OF GASEOUS PARTICLE DETECTORS ETC. 5Fig. 6. – Random counting rate as a function of high voltage.4. – Experimental testThe characterization of the first prototype was carried out at the Beam Test Facility(BTF) of the National Laboratories of Frascati with a beam of 450 MeV electrons. Theaverage multiplicity of particles per bunch was fixed at 0.3 for the whole duration of thetest. Two silicon detectors optimized for time-of-flight measurements have been used asthe trigger reference. The trigger-time resolution has been measured during the test,resulting in (180±4) ps. A summary of the results is shown in fig. 4. The time resolutionhas been evaluated by measuring the jitter of the electron time of flight with respectto one silicon detector, corrected for the time-walk effect. A jitter of (590 ± 90) ps wasmeasured. The “efficiency times acceptance” curve shows a knee at about 5600 V.The characterization of the second prototype was carried out at INFN laboratoriesof Rome Tor Vergata using atmospheric muons. Two scintillators have been used asthe trigger reference. The trigger-time resolution has been measured during the test,resulting in (456 ± 14) ps. The final results are shown in fig. 5. The time resolution hasbeen evaluated as described above: a jitter of (1.10 ± 0.09) ns has been measured. The“efficiency times acceptance” curve shows a knee point at about 6200 V.Random counting rate has been measured by acquiring waveforms in a 10 μs timewindow. The results are shown in fig. 6. The high random counting rate is ascribed tothe roughness and the imperfection of the spacers.6 A. ROCCHI et al.5. – ConclusionsThe results obtained in these preliminary tests provide a solid foundation for thedevelopment of a new type of RPC detector. The efficiency knee as well as the timeresolution are consistent with the standard RPC performances in spite of the extremelyhigh random counting rate. For an experimental confirmation of the rate capabilityincrease a test has been planned. Further studies are needed to investigate the detectorstability and the interactions between the gas mixture components and the electrodesurface.∗ ∗ ∗This research is conducted under the supervision of Prof. R. Cardarelli at the INFNRoma Tor Vergata laboratory. The authors express their fond thanks to Luigi Di Stante(University of Roma “Tor Vergata”) for his technical support.REFERENCES[1] ATL-COM-MUON-2017-033, July 7, 2017.[2] FCC-hh design study, https://fcc.web.cern.ch/Pages/fcc-hh.aspx.[3] Santonico R. and Cardarelli R., Nucl. Instrum. Methods, 187 (1981) 377.[4] Cardarelli R. and Santonico R., Nucl. Instrum. Methods, 200 (1988) 263.[5] Cardarelli R. et al., JINST, 8 (2013) P01003.[6] Benoit M. et al., JINST, 11 (2016) P03011.

Development of gaseous particle detectors based on semi-conductive electrode plates

A new kind of particle detector based on a Resistive Plate Chamber structure is under development. Semi-conductive electrodes with resistivity up to 108 Ω cm are introduced to improve the Rate Capability performance. In this paper some results on the configurations under test are described. The DC Voltamperometric characterization of a SI-GaAs sample measured applying metal electrodes on the substrate is also reported

Di Ciaccio, A.

DOI 10.1393/ncc/i2018-18085-8Colloquia: IFAE 2017IL NUOVO CIMENTO 41 C (2018) 85Development of gaseous particle detectors based onsemi-conductive plate electrodesA. Rocchi(1), R. Cardarelli(2), S. Bruno(1), A. Caltabiano(1), P. Camarri(1),A. Di Ciaccio(1) and L. Pizzimento(1)(1) Università di Roma Tor Vergata - Via della ricerca scientifica 1, Roma, Italy(2) INFN, Sezione Roma 2 - Via della ricerca scientifica 1, Roma, Italyreceived 21 April 2018Summary. — A new kind of particle detector based on a Resistive Plate Chamberstructure is under development. Semi-conductive electrodes with resistivity up to108 Ω cm are introduced to improve the Rate Capability performance. In this papersome results on the configurations under test are described. The DC Voltampero-metric characterization of a SI-GaAs sample measured applying metal electrodes onthe substrate is also reported.1. – Increasing the rate capabilityWhen a particles flux Φ passes through an RPC detector [1], the simultaneous ignitionof many unit cells occurs, whose cumulative effect causes a voltage drop on the electrodesdescribed by eq. (1), with 〈Q〉 mean charge involved in a single process, Φeff numberof process occurring in the detector per unit time and surface, ρ electrode resistivity,d electrode thickness(1) V − Vgas = 2ρd〈Q〉Φeff.To prevent the detector from losing efficiency as the flux rises, it is necessary to minimizethe voltage drop on the electrodes. For this purpose in this test the combination of twostrategies was used:• Reduction of the average charge 〈Q〉 using a high Signal-to-Noise ratio chargeamplifier [2].• Replacement of standard insulating electrodes with Semi-Insulating electrodes withlower resistivity and thickness of 400 μm.Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 A. ROCCHI et al.(a) (b)Fig. 1. – (a)Time difference with respect to the trigger detector [3] corrected for the Time Walkeffect (HV = 5630 V) (b) Efficiency × acceptance, 450 MeV electrons, 1 mm gas gap.2. – Experimental testThe prototype is made of two SI-GaAs electrodes spaced by a PET circular crown1 mm thick. Both electrodes are 400 μm thick and have a resistivity on the order of108 Ω cm. The gas gap is filled with a gas mixture consisting of TFE-iC4H10-SF6(95%/4.5%/0.5%). The detector is placed in series with a 100 MΩ resistance in order toavoid that the power dissipated in the electrode, due to any shock related to edge defects,damage the crystal. The signal is read on a pad placed under the low-voltage electrode.The prototype characterization was carried out at the BTF of the National Laborato-ries of Frascati, using 450MeV electron beam. The average multiplicity of particles perbunch was fixed at 0.3 for the whole duration of the test. In fig. 1 the experimentalobservations are shown. Taking into account the trigger time resolution of (180 ± 4) ps,a time resolution of (590 ± 90) ps was measured.A second prototype with 1.5mm gas gap, one silicon electrode and one SI-GaAs elec-trode, has been investigated with atmospheric muons. In this case a time resolution of(1.10 ± 0.09) ns was measured. These results provide a solid foundation for the develop-ment of new prototypes. Efficiency × acceptance curves, as well as the time resolution,are consistent with what observed in a standard RPC detector. For an experimentalconfirmation of the increase in terms of Rate Capability, a test with a source of photonhas been planned.∗ ∗ ∗The authors acknowledge Luigi Di Stante and Barbara Liberti for their technical andscientific support.REFERENCES[1] Santonico R. and Cardarelli R., Nucl. Instrum. Methods, 187 (1981) 377.[2] Cardarelli R. et al., JINST, 8 (2013) P01003.[3] Benoit M. et al., JINST, 11 (2016) P03011.

Development of gaseous particle detectors based on

semi-conductive plate electrodes

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Development of gaseous particle detectors based on semi-conductive electrode plates

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