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Small-pads resistive Micromegas prototype
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Small-pads resistive Micromegas prototype C. Di Donato a ,∗, M. Alviggi b , M.T. Camerlingo c , V. Canale b , M. Della Pietra b , P. Iengo d , M. Iodice c , F. Petrucci c , G. Sekhniaidze b a
Universitá Parthenope e Sezione INFN di Napoli, Italy Universitá Federico II e Sezione INFN di Napoli, Italy c Universitá e Sezione INFN di Roma Tre, Italy d CERN, Switzerland b
ARTICLE
INFO
Keywords: Gas detectors Micromegas Micro-pattern gas detectors
ABSTRACT Detectors at future accelerators will require operation at rates up to three orders of magnitude higher than 15 kHz/cm2 the hit rates expected in the current upgrades forward muon detectors of LHC experiments. A resistive Micromegas detectors with modified readout system can achieve rate capability up to few MHz/cm2 low occupancy. We present the development of small-pad Micromegas detectors with a pad resistive readout of few mm2 in size, built with the spark protection resistive layer realized with different techniques.
1. Introduction Micromegas Detectors are based on a double gas gap structure, drift and amplification regions, where ionization and avalanche multiplication take place, respectively. The first resistive Micromegas detectors [1], with rate capability up to few kHz/cm2 , were developed with strip readout plane for the ATLAS New Small Wheel, muon spectrometer upgrade [2]. High Energy Physics experiments at future colliders will require rate capability up to few MHz/cm2 . In order to improve the rate capability up to this requirement a careful optimization of the resistive protection system and a finer read-out (pixel/pad) are necessary [3]. 2. Detectors structure Fig. 1. Picture of detector anode; zoom on readout pattern detector.
The readout pattern detector is a matrix with 48 × 16 rectangular pads, 0.8 × 2.8 mm2 , with a pitch of 1 and 3 mm (Fig. 1), resulting in 768 readout channels, for a total active area of 48 × 48 mm2 . There are 48 pads along the precision coordinate, defined by the 1 mm pad pitch and 16 pads along the orthogonal direction. Two different spark protection resistive layer have been tested: in the first one the resistive layers have been deposited with screen printing and the anode pads are overlaid by resistive pads, both interconnected by intermediate embedded resistors, (resistance 3–7 MOhm), for charge evacuation (Fig. 2.a), the signal is transmitted by capacitive coupling; in the second one a uniform Diamond Like Carbon structure (DLC) has been done by sputtering, resulting in two continuous resistive DLC layers, interconnected between them and to the readout pads with network of conducting links with the pitch of few mm, to evacuate
the charge, (Fig. 2.b). DLC foils resistivity is about 50 MOhm/sq (DLC-High prototype). We show preliminary results for a new DLC prototype with a lower resistivity, about 20 MOhm/sq (DLC-Low). In the measurements presented we use Ar–CO2 (93%–7%) gas mixture. Detector characterization. Detectors have been extensively tested in the laboratory of the RD51 collaboration [4] at CERN, using different radiation sources and measuring their performances in different conditions [3]. Detectors have been operated with the anode pads connected to ground, whit mesh and cathode powered with negative voltages. The gain has been measured with two methods, first analyzing signals from mesh with a MultiChannel Analyzer, second reading the
∗ Correspondence to: Universitá Parthenope Napoli, Centro Direzionale Is. C4, 80143 Napoli, Italy. E-mail addresses: [email protected], [email protected] (C.D. Donato).
https://doi.org/10.1016/j.nima.2019.162799 Received 8 April 2019; Accepted 16 September 2019 Available online xxxx 0168-9002/© 2019 Published by Elsevier B.V.
Please cite this article as: C.D. Donato, M. Alviggi, M.T. Camerlingo et al., Small-pads resistive Micromegas prototype, Nuclear Inst. and Methods in Physics Research, A (2019) 162799, https://doi.org/10.1016/j.nima.2019.162799.
C.D. Donato, M. Alviggi, M.T. Camerlingo et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Fig. 2. Schematic side view for the two prototypes.
Fig. 5. Residuals distribution between expected and reconstructed cluster position for precision coordinate; Embedded-Resistor prototype with the amplification voltage of 530 V.
Fig. 3. Energy spectra for 55 Fe source: energy resolution, defined as the ratio between FWHM and peak value, is 36% (Embedded-Resistor), and 14% (DLC-High).
Fig. 4. Detector gain as a function of the amplification voltage: Red dots indicate the curve measured for Embedded-Resistor prototype with ’’High Activity’’ source.
drop of about 20%, when the detector is exposed to the High activity 55 Fe source, (see Fig. 4). The gain drop is due to a local reduction of the amplification field, due to the charge-up of dielectric. DLC-Layer prototype is not affected by this problem, because of the different structure. The detectors response to increasing incoming particle flux, has been measured using an X-ray gun; photons have been focused in order to explore a large rate range up to 150 MHz/cm2 . The EmbeddedResistor prototype, using amplification voltage of 530 V, shows a gain as a function of the photon rate measured for a gain reduction of about 20% with X-rays at ≃10 MHz/cm2 , and a gain reduction of about 40% for rate well above 150 MHz/cm2 , but at this rate the gain is still about 4000. The DLC prototype shows a gain behavior which slightly depends from the pitch of the conducting vias, between the two layers and the readout pads; as expected the farer is the connection to the ground, the higher is the resistance of connection and the voltage drop of the anode with respect to the mesh, thus producing a lower amplification electric field.
detector current from readout pads with a pico-ammeter and counting signal rate from the mesh. Measurements have been performed on both prototypes using two different radiation sources: 55 Fe and X-rays. Low rate measurements have been performed using 55 Fe sources with two different activities, ’’Low activity’’ (1.3 kHz) and ’’High activity’’ (128 kHz); high rate measurements have been performed using 8 keV X-rays peak from a Cu target, tuning the intensity of the X-rays gun by varying the excitation current. The different behavior of charge spectra for the two prototypes, Fig. 3, is due to the spark protection resistive layer implemented: the DLC-Layer detector has a more uniform electric field in proximity of the resistive layer, while the pad-patterned layout of the other detector produces strong variations of the electric field along the border of the resistive pads, thus getting the energy resolution worse. The energy resolution, defined as the ratio between FWHM and peak value, for the Embedded-Resistor prototype is about 36%, while for the DLCHigh detector is about 14%; preliminary results on the new prototype DLC-Low give a promising energy resolution of about 12%. Gain measurements, as a function of the amplification voltage, has been performed using Low and High activity 55 Fe source. Results for the two prototypes are consistent, but the Embedded-Resistor shows a gain
Test beam. Detector performance, including efficiency and spatial resolution, have been studied in dedicated measurement campaigns at SPS facility at CERN, with high energy muon beam. External Tracking System with scintillator hodoscope for triggering incoming particles has been combined with two Micromegas with strip segmented anode with double view as tracking chambers. The clusters on the pad detector have been reconstructed combining the charge information from neighboring fired pads [3]. The spatial resolution has been evaluated comparing the cluster position reconstructed on the detector and the expected hit position obtained from tracking detectors. The distribution of the residuals, in the precision coordinate (1 mm pad pitch), as measured with the high energy muon beam, is reported. A residuals distribution width of 190 μm was obtained performing a Gaussian fit for the Embedded-Resistor prototype, Fig. 5. Residuals distribution in the precision coordinate for DLC-High has a 120 μm width A residuals distribution width of 90 μm was obtained performing a Gaussian fit for the DLC-Low prototype, Fig. 6. The preliminary analysis for DLC-Low shows significant improvement of spatial resolution, compared to DLC-High prototype (Fig. 7). Due to the lower resistivity, the number of pads per cluster in DLCLow is larger than in the DLC-High, this has the advantage to improve the charge weighted centroid position measurement, on the other side the occupancy increases as well, which is not desirable under very high rates. 2
Please cite this article as: C.D. Donato, M. Alviggi, M.T. Camerlingo et al., Small-pads resistive Micromegas prototype, Nuclear Inst. and Methods in Physics Research, A (2019) 162799, https://doi.org/10.1016/j.nima.2019.162799.
C.D. Donato, M. Alviggi, M.T. Camerlingo et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Fig. 7. Resolution as a function of the amplification voltage; DLC2 is DLC-Low, while DLC0 is DLC-High Resolution. Preliminary results on DLC-Low show improvement in spatial resolution, compared to DLC-High prototype.
Fig. 6. Residuals distribution between expected and reconstructed cluster position for precision coordinate; DLC-Low prototype with the amplification voltage of 520 V.
Acknowledgments
Conclusion. Different Micromegas with small resistive pads readout have been designed, built and tested. Prototypes differ from each other by the layout of the resistive spark protection layer, one with a pad patterned embedded resistors and the other with a uniform DLC layer. Both configurations show a very good efficiency and a good spatial resolution, in the more accurate coordinate. DLC compared to the Embedded-Resistor prototype shows a better energy resolution and a similar rate capability. Due to the promising results obtained, DLC prototype has been implemented in two version: DLC-High and DLCLow, which differ by the DLC foils resistivity, about 50 MOhm/sq and 20 MOhm/sq. Preliminary measurements on DLC prototype with a lower resistivity show a more uniform charge distribution among pads in the detector, resulting in significant improvement of spatial resolution, compared to DLC-High prototype.
We would like to thank the CERN MPT Workshop (R. De Oliveira and A. Teixeira for ideas, discussions and construction of the detectors), the RD51 Collaboration for support with tests 198 at the GDD Lab and at H4 SPS beam line. References [1] T. Alexopoulos, J. Burnens, et al., A spark-resistant bulk-micromegas chamber for high-rate applications, Nucl. Instrum. Methods A 640 (2011) 110, http://dx.doi. org/10.1016/j.nima.2011.03.025. [2] A. Collaboration, New small wheel technical design report, CERN-LHCC-2013-006. [3] M. Alviggi, et al., Construction and test of a small-pad resistive micromegas prototype, J. Instrum. 13 (2018) P11019, http://dx.doi.org/10.1088/1748-0221/ 13/11/P11019. [4] Collaboration-RD51, Proposal development of micro-pattern gas detector technologies, CERN-LHCC-2008-011.
3
Please cite this article as: C.D. Donato, M. Alviggi, M.T. Camerlingo et al., Small-pads resistive Micromegas prototype, Nuclear Inst. and Methods in Physics Research, A (2019) 162799, https://doi.org/10.1016/j.nima.2019.162799.
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Small-pads resistive Micromegas prototype C. Di Donato a ,∗, M. Alviggi b , M.T. Camerlingo c , V. Canale b , M. Della Pietra b , P. Iengo d , M. Iodice c , F. Petrucci c , G. Sekhniaidze b a
Universitá Parthenope e Sezione INFN di Napoli, Italy Universitá Federico II e Sezione INFN di Napoli, Italy c Universitá e Sezione INFN di Roma Tre, Italy d CERN, Switzerland b
ARTICLE
INFO
Keywords: Gas detectors Micromegas Micro-pattern gas detectors
ABSTRACT Detectors at future accelerators will require operation at rates up to three orders of magnitude higher than 15 kHz/cm2 the hit rates expected in the current upgrades forward muon detectors of LHC experiments. A resistive Micromegas detectors with modified readout system can achieve rate capability up to few MHz/cm2 low occupancy. We present the development of small-pad Micromegas detectors with a pad resistive readout of few mm2 in size, built with the spark protection resistive layer realized with different techniques.
1. Introduction Micromegas Detectors are based on a double gas gap structure, drift and amplification regions, where ionization and avalanche multiplication take place, respectively. The first resistive Micromegas detectors [1], with rate capability up to few kHz/cm2 , were developed with strip readout plane for the ATLAS New Small Wheel, muon spectrometer upgrade [2]. High Energy Physics experiments at future colliders will require rate capability up to few MHz/cm2 . In order to improve the rate capability up to this requirement a careful optimization of the resistive protection system and a finer read-out (pixel/pad) are necessary [3]. 2. Detectors structure Fig. 1. Picture of detector anode; zoom on readout pattern detector.
The readout pattern detector is a matrix with 48 × 16 rectangular pads, 0.8 × 2.8 mm2 , with a pitch of 1 and 3 mm (Fig. 1), resulting in 768 readout channels, for a total active area of 48 × 48 mm2 . There are 48 pads along the precision coordinate, defined by the 1 mm pad pitch and 16 pads along the orthogonal direction. Two different spark protection resistive layer have been tested: in the first one the resistive layers have been deposited with screen printing and the anode pads are overlaid by resistive pads, both interconnected by intermediate embedded resistors, (resistance 3–7 MOhm), for charge evacuation (Fig. 2.a), the signal is transmitted by capacitive coupling; in the second one a uniform Diamond Like Carbon structure (DLC) has been done by sputtering, resulting in two continuous resistive DLC layers, interconnected between them and to the readout pads with network of conducting links with the pitch of few mm, to evacuate
the charge, (Fig. 2.b). DLC foils resistivity is about 50 MOhm/sq (DLC-High prototype). We show preliminary results for a new DLC prototype with a lower resistivity, about 20 MOhm/sq (DLC-Low). In the measurements presented we use Ar–CO2 (93%–7%) gas mixture. Detector characterization. Detectors have been extensively tested in the laboratory of the RD51 collaboration [4] at CERN, using different radiation sources and measuring their performances in different conditions [3]. Detectors have been operated with the anode pads connected to ground, whit mesh and cathode powered with negative voltages. The gain has been measured with two methods, first analyzing signals from mesh with a MultiChannel Analyzer, second reading the
∗ Correspondence to: Universitá Parthenope Napoli, Centro Direzionale Is. C4, 80143 Napoli, Italy. E-mail addresses: [email protected], [email protected] (C.D. Donato).
https://doi.org/10.1016/j.nima.2019.162799 Received 8 April 2019; Accepted 16 September 2019 Available online xxxx 0168-9002/© 2019 Published by Elsevier B.V.
Please cite this article as: C.D. Donato, M. Alviggi, M.T. Camerlingo et al., Small-pads resistive Micromegas prototype, Nuclear Inst. and Methods in Physics Research, A (2019) 162799, https://doi.org/10.1016/j.nima.2019.162799.
C.D. Donato, M. Alviggi, M.T. Camerlingo et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Fig. 2. Schematic side view for the two prototypes.
Fig. 5. Residuals distribution between expected and reconstructed cluster position for precision coordinate; Embedded-Resistor prototype with the amplification voltage of 530 V.
Fig. 3. Energy spectra for 55 Fe source: energy resolution, defined as the ratio between FWHM and peak value, is 36% (Embedded-Resistor), and 14% (DLC-High).
Fig. 4. Detector gain as a function of the amplification voltage: Red dots indicate the curve measured for Embedded-Resistor prototype with ’’High Activity’’ source.
drop of about 20%, when the detector is exposed to the High activity 55 Fe source, (see Fig. 4). The gain drop is due to a local reduction of the amplification field, due to the charge-up of dielectric. DLC-Layer prototype is not affected by this problem, because of the different structure. The detectors response to increasing incoming particle flux, has been measured using an X-ray gun; photons have been focused in order to explore a large rate range up to 150 MHz/cm2 . The EmbeddedResistor prototype, using amplification voltage of 530 V, shows a gain as a function of the photon rate measured for a gain reduction of about 20% with X-rays at ≃10 MHz/cm2 , and a gain reduction of about 40% for rate well above 150 MHz/cm2 , but at this rate the gain is still about 4000. The DLC prototype shows a gain behavior which slightly depends from the pitch of the conducting vias, between the two layers and the readout pads; as expected the farer is the connection to the ground, the higher is the resistance of connection and the voltage drop of the anode with respect to the mesh, thus producing a lower amplification electric field.
detector current from readout pads with a pico-ammeter and counting signal rate from the mesh. Measurements have been performed on both prototypes using two different radiation sources: 55 Fe and X-rays. Low rate measurements have been performed using 55 Fe sources with two different activities, ’’Low activity’’ (1.3 kHz) and ’’High activity’’ (128 kHz); high rate measurements have been performed using 8 keV X-rays peak from a Cu target, tuning the intensity of the X-rays gun by varying the excitation current. The different behavior of charge spectra for the two prototypes, Fig. 3, is due to the spark protection resistive layer implemented: the DLC-Layer detector has a more uniform electric field in proximity of the resistive layer, while the pad-patterned layout of the other detector produces strong variations of the electric field along the border of the resistive pads, thus getting the energy resolution worse. The energy resolution, defined as the ratio between FWHM and peak value, for the Embedded-Resistor prototype is about 36%, while for the DLCHigh detector is about 14%; preliminary results on the new prototype DLC-Low give a promising energy resolution of about 12%. Gain measurements, as a function of the amplification voltage, has been performed using Low and High activity 55 Fe source. Results for the two prototypes are consistent, but the Embedded-Resistor shows a gain
Test beam. Detector performance, including efficiency and spatial resolution, have been studied in dedicated measurement campaigns at SPS facility at CERN, with high energy muon beam. External Tracking System with scintillator hodoscope for triggering incoming particles has been combined with two Micromegas with strip segmented anode with double view as tracking chambers. The clusters on the pad detector have been reconstructed combining the charge information from neighboring fired pads [3]. The spatial resolution has been evaluated comparing the cluster position reconstructed on the detector and the expected hit position obtained from tracking detectors. The distribution of the residuals, in the precision coordinate (1 mm pad pitch), as measured with the high energy muon beam, is reported. A residuals distribution width of 190 μm was obtained performing a Gaussian fit for the Embedded-Resistor prototype, Fig. 5. Residuals distribution in the precision coordinate for DLC-High has a 120 μm width A residuals distribution width of 90 μm was obtained performing a Gaussian fit for the DLC-Low prototype, Fig. 6. The preliminary analysis for DLC-Low shows significant improvement of spatial resolution, compared to DLC-High prototype (Fig. 7). Due to the lower resistivity, the number of pads per cluster in DLCLow is larger than in the DLC-High, this has the advantage to improve the charge weighted centroid position measurement, on the other side the occupancy increases as well, which is not desirable under very high rates. 2
Please cite this article as: C.D. Donato, M. Alviggi, M.T. Camerlingo et al., Small-pads resistive Micromegas prototype, Nuclear Inst. and Methods in Physics Research, A (2019) 162799, https://doi.org/10.1016/j.nima.2019.162799.
C.D. Donato, M. Alviggi, M.T. Camerlingo et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Fig. 7. Resolution as a function of the amplification voltage; DLC2 is DLC-Low, while DLC0 is DLC-High Resolution. Preliminary results on DLC-Low show improvement in spatial resolution, compared to DLC-High prototype.
Fig. 6. Residuals distribution between expected and reconstructed cluster position for precision coordinate; DLC-Low prototype with the amplification voltage of 520 V.
Acknowledgments
Conclusion. Different Micromegas with small resistive pads readout have been designed, built and tested. Prototypes differ from each other by the layout of the resistive spark protection layer, one with a pad patterned embedded resistors and the other with a uniform DLC layer. Both configurations show a very good efficiency and a good spatial resolution, in the more accurate coordinate. DLC compared to the Embedded-Resistor prototype shows a better energy resolution and a similar rate capability. Due to the promising results obtained, DLC prototype has been implemented in two version: DLC-High and DLCLow, which differ by the DLC foils resistivity, about 50 MOhm/sq and 20 MOhm/sq. Preliminary measurements on DLC prototype with a lower resistivity show a more uniform charge distribution among pads in the detector, resulting in significant improvement of spatial resolution, compared to DLC-High prototype.
We would like to thank the CERN MPT Workshop (R. De Oliveira and A. Teixeira for ideas, discussions and construction of the detectors), the RD51 Collaboration for support with tests 198 at the GDD Lab and at H4 SPS beam line. References [1] T. Alexopoulos, J. Burnens, et al., A spark-resistant bulk-micromegas chamber for high-rate applications, Nucl. Instrum. Methods A 640 (2011) 110, http://dx.doi. org/10.1016/j.nima.2011.03.025. [2] A. Collaboration, New small wheel technical design report, CERN-LHCC-2013-006. [3] M. Alviggi, et al., Construction and test of a small-pad resistive micromegas prototype, J. Instrum. 13 (2018) P11019, http://dx.doi.org/10.1088/1748-0221/ 13/11/P11019. [4] Collaboration-RD51, Proposal development of micro-pattern gas detector technologies, CERN-LHCC-2008-011.
3
Please cite this article as: C.D. Donato, M. Alviggi, M.T. Camerlingo et al., Small-pads resistive Micromegas prototype, Nuclear Inst. and Methods in Physics Research, A (2019) 162799, https://doi.org/10.1016/j.nima.2019.162799.