- Email: [email protected]
TPCs of the T2K experiment
Nuclear Instruments and Methods in Physics Research A 623 (2010) 105–107
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Production and calibration of 9 m2 of bulk-micromegas detectors for the readout of the ND280/TPCs of the T2K experiment A. Delbart CEA/CE-Saclay, DSM-IRFU, 91191 Gif sur Yvette Cedex, France
on behalf of the T2K/TPC Collaboration a r t i c l e in fo
abstract
Available online 4 March 2010
The near detector ND280 of the long baseline neutrino experiment T2K (JPARC, Japan) will contain three large 5 m3 time projection chambers (TPC) for charged particles tracking and identification. These TPCs will be the first large TPCs readout by micro pattern gaseous detectors (MPGD). The bulk-Micromegas MPGD is a micro mesh gaseous structure (MicroMeGaS) in which the woven micromesh is embedded on top of the segmented anode plane of the MPGD by use of standard photolithographic techniques. This MPGD was chosen for its performances in terms of gas gain uniformity, energy resolution and space point resolution, and for its capability to efficiently pave large readout surfaces with minimized dead zones. We developed and improved the bulk-micromegas production methods to be suitable for a uniform, cheap and high quality mass production of 34 36 cm2 bulk-micromegas modules of 1726 pads. Production of 72 bulk-micromegas modules, for an equivalent total readout surface of 9 m2, began in may 2008 at CERN. After the description of a module and its production, we report on the pad per pad calibration with a strong 55Fe X-ray source of the 32 bulk-micromegas produced so far. Gas gain and 5.9 keV energy resolution are presented to illustrate their good uniformity within the whole surface of each module (2.8% and 6% r.m.s dispersion, respectively) and their good reproducibility from one module to another (8% and 3% r.m.s, respectively). & 2010 Elsevier B.V. All rights reserved.
Keywords: T2K TPC MPGD Micromegas Bulk-micromegas
1. Introduction The T2K experiment is a long baseline experiment dedicated to the precise measurement of the mixing angle y13 through the observation of nm ne oscillations [1]. The 0.2 T magnetized near detector (ND280) of the experiment will measure the neutrino flux and spectrum as well as the ne contamination in the beam at JPARC (Tokai, Japan). It contains three large 2.4 0.9 2.5 m3 TPCs that will measure tracks produced in the fine grained detectors [2]. Each TPC has two 2.4 0.9 m2 readout planes on both sides of the central cathode and each readout plane is paved by 12 bulk-micromegas modules, for an equivalent total surface of 9 m2. The inner and outer sides of a readout plane are shown in Fig. 1. The TPC is operated with Ar(95%)–CF4(3%)–isobutane(2%) gas mixture and ionization electrons are drifted for up to 1m under an electric field of 200 V/cm. After 3 years of R&D, the final design of a module was validated by cosmic rays tests performed on the HARP TPC cage in November 2007. The required performance of a better than 10% momentum resolution at a
momentum of 1 GeV/c, and a better than 10% dE/dx resolution for good particle identification, were achieved [3,4]. The production of the 72 bulk-micromegas, the 124 416 Front-End AFTER Electronics channels [5] and the 3 TPC cages began 1 year ago. The first TPC was equipped with 24 bulk-micromegas modules and Front-End Electronics and tested with cosmics and muon beam at TRIUMF [6]. The 3 TPCs will be commissioned at JPARC at the end of 2009. We report on the production and calibration of the 32 bulk-micromegas modules produced so far.
2. Description and production of the T2K/TPC bulkmicromegas modules The technique for manufacturing all-in-one micromegas detectors, called bulk-micromegas, has been developed by a collaboration between CERN/TS-DEM and IRFU (CEA-Saclay) [7]. The T2K bulk-micromegas is made of a 430 Lines/in., 30 mm thick, 304 L stainless steel woven mesh1 which is laminated on top of the anode Printed Circuit Board covered by a photo-imageable
Tel.: + 33 1 69 08 3454; fax: + 33 1 69 08 3024.
E-mail address: [email protected] 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.163
1
BOPP, Bachmannweg 21, CH-8046, Zurich, Switzerland (www.bopp.ch).
106
A. Delbart / Nuclear Instruments and Methods in Physics Research A 623 (2010) 105–107
polyimide film. The PCB is 2.2 mm thick and made of four copper layers for anode pads, routing net, grounding and pad-readout connectors. During the lamination, the micromesh is held on an external frame with a tension of 12 N in order to guarantee a good flatness of the micromesh and thereby a uniform micromegas amplification gap of 128 mm. At the end of the process, the detector is cut at its final 34 36 cm2 dimensions. The micromesh is held by a 2 mm coverlay border surrounding the detector’s active area and by 20 736 regularly distributed pillars, maintaining the amplification gap of 128 mm. The pillars, 12 per pad, are cylindrical with a diameter of 0.5 mm [4]. The 6.85 9.65 mm2 pads are arranged in 48 rows of 36 pads each apart from a corner where a two pads equivalent surface is reserved for the micromesh high voltage supply connection from the backside of the PCB (Fig. 2). Ninety-five percent of the surface of a module and more than 85% of the surface of a readout plane is active area.
Fig. 1. A TPC readout plane equipped with 12 micromegas modules and Front-End AFTER Electronics, seen from the inner side of the TPC (left) and seen from the outside of the TPC (right).
These bulk-micromegas MPGD are therefore well suited to pave large detection surfaces with minimal dead zones and minimal drift electric field distortions between modules. The complete production sequence of a T2K/TPC bulk micromegas module is described in Fig. 3. Eight bulk-micromegas are produced per month at CERN/TS-DEM-PMT with several mechanical and electrical quality controls performed at critical steps. Once qualified with a measured global mesh current below 2 nA at 600 V in air, the bulk-micromegas is cut at its final dimensions and equipped with the 24 pad-readout connectors. The bulk-micromegas is then transferred to the T2K/TPC production lab at CERN where it is first glued in class 1000 clean room on a FR5 mechanical stiffener with control of the stiffener’s gasket-tomicromegas’ mesh dimension at 750 mm. This is required to guarantee the proper location and flatness of the micromesh of the 12 modules of a TPC readout plane and thereby a uniform drift electric field. The detector is then inserted into a gas-tight test box filled with dry air and forced to spark by gradually increasing the mesh high-voltage. This way, most of the dusts are burnt, and most of the tiny surface asperities of the micromesh and/or the copper pads are smoothed. This procedure was proved to greatly lower the natural sparking rate of the detector in T2K/TPC gas for a given high-voltage on the micromesh, leading to a safer operation of the detector in the experiment. The quality of the first 32 modules produced is very high: all the detectors sustain up to 900 V in dry-air (70 kV/cm) and four of them have one pad in short-circuit with the mesh (four dead pads over 55 232). The production yield of the anode PCBs is 83% to achieve the stringent Q/C criteria (no electrical defects and PCB thickness within specifications) and the production yield of the bulk-micromegas (including the mesh integration, the final detector’s cutting and the connectors’ soldering) is 4 90%. The last stage of the production is the calibration of the modules on a dedicated automatized test bench. 3. Calibration of the micromegas modules
Fig. 2. T2K/TPC bulk-micromegas module.
Fig. 3. Production sequence of a T2K/TPC bulk-micromegas module.
The purpose of the calibration is to measure the average gain and 5.9 keV resolution with a 370 MBq 55Fe X-ray source for each of the 1726 pads of a module and in the operating conditions of the detector in the T2K/TPC:T2K/TPC gas mixture, AFTER based front-end electronics [5], operating mesh high voltage of 350 V (which corresponds to a micromegas gas gain of around 1700 and a S/N ratio 4200) and 200 V/cm drift electric field. The core of the test bench is a gas chamber designed to define a uniform 4 cm drift electric field and filled with 10 l/h gas flow at 1 mbar above atmospheric pressure. A X–Y motorized holder allows to precisely position the source in front of each pad (Fig. 4). A complete scan of a module is done in around 6 h with 1000 events acquired for each pad. A gain vs mesh high voltage curve ( 320 up to 370 V) is also done for a group of pads in the middle of the module.
Fig. 4.
55
Fe X-ray source calibration test bench.
A. Delbart / Nuclear Instruments and Methods in Physics Research A 623 (2010) 105–107
Fig. 5. Typical gain vs high-voltage curve (left) and
107
55
Fe X-ray source spectrum (right) of a T2K/TPC micromegas detector.
Fig. 6. Typical 2D-map of collected charge (top left) with the corresponding distribution over the 1726 pads (bottom left) and typical 2D-map of r.m.s 5.9 keV resolution (top right) with the corresponding distribution over the 1726 pads (bottom right). Channel (0;30) is a dead electronics channel and the two pads in the bottom right corner are used for mesh HV connection.
Taken from the calibration of the first 32 modules produced so far, a typical 55Fe X-ray source spectrum is shown in Fig. 5 with a 5.9 keV r.m.s resolution of 9%. 2D-maps of collected charge and 5.9 keV energy resolution for each of the 1726 pads of a module are shown in Fig. 6. The typical r.m.s dispersion of collected charge is 2.8% over the whole surface of a detector and the r.m.s dispersion of the average gain of the 32 detectors is 8%. The typical r.m.s dispersion of the 5.9 keV energy resolution is 6% over the whole surface of a detector and the r.m.s dispersion of the average 5.9 keV resolution of the 32 detectors is 3%. Eighty-five percent of the detectors are ‘‘top quality’’ with typical 2D maps shown in Fig. 6, the remaining 15% can present up to 14% 5.9 keV resolution for o 10 pads ( o 1% of the active area). A typical 0.1 spark/hour sparking rate is observed at 350 V mesh voltage in a 1 cm drift chamber. All these figures were corrected for pad capacitance dispersion but not yet for temperature and pressure variations.
4. Conclusion Production of 72 bulk-micromegas modules for the TPCs of the T2K experiment began in May 2008 at CERN and should be completed by summer 2009. The pad per pad calibration of the first 32 modules shows a very good uniformity and reproducibility of performances for both gas gain and 5.9 keV energy resolution. This proves that the bulk-micromegas is becoming a mature technology well suited for high quality and large scale production of large active area MPGDs. References [1] [2] [3] [4] [5] [6] [7]
Y. Itow, et al., hep-ex/0106019. R. Tacik, The T2K fine-grained detectors, these proceedings. J. Bouchez, et al., Nucl. Instr. and Meth. A 574 (2007) 425. S. Anvar, et al., Nucl. Instr. and Meth. A 602 (2009) 415. P. Baron, et al., IEEE Trans. Nucl. Sci. NS-55 (2008) 1744. D. Karlen, Time projection chambers for the T2K experiment, these proceedings. I. Giomataris, et al., Nucl. Instr. and Meth. A 560 (2006) 405.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Production and calibration of 9 m2 of bulk-micromegas detectors for the readout of the ND280/TPCs of the T2K experiment A. Delbart CEA/CE-Saclay, DSM-IRFU, 91191 Gif sur Yvette Cedex, France
on behalf of the T2K/TPC Collaboration a r t i c l e in fo
abstract
Available online 4 March 2010
The near detector ND280 of the long baseline neutrino experiment T2K (JPARC, Japan) will contain three large 5 m3 time projection chambers (TPC) for charged particles tracking and identification. These TPCs will be the first large TPCs readout by micro pattern gaseous detectors (MPGD). The bulk-Micromegas MPGD is a micro mesh gaseous structure (MicroMeGaS) in which the woven micromesh is embedded on top of the segmented anode plane of the MPGD by use of standard photolithographic techniques. This MPGD was chosen for its performances in terms of gas gain uniformity, energy resolution and space point resolution, and for its capability to efficiently pave large readout surfaces with minimized dead zones. We developed and improved the bulk-micromegas production methods to be suitable for a uniform, cheap and high quality mass production of 34 36 cm2 bulk-micromegas modules of 1726 pads. Production of 72 bulk-micromegas modules, for an equivalent total readout surface of 9 m2, began in may 2008 at CERN. After the description of a module and its production, we report on the pad per pad calibration with a strong 55Fe X-ray source of the 32 bulk-micromegas produced so far. Gas gain and 5.9 keV energy resolution are presented to illustrate their good uniformity within the whole surface of each module (2.8% and 6% r.m.s dispersion, respectively) and their good reproducibility from one module to another (8% and 3% r.m.s, respectively). & 2010 Elsevier B.V. All rights reserved.
Keywords: T2K TPC MPGD Micromegas Bulk-micromegas
1. Introduction The T2K experiment is a long baseline experiment dedicated to the precise measurement of the mixing angle y13 through the observation of nm ne oscillations [1]. The 0.2 T magnetized near detector (ND280) of the experiment will measure the neutrino flux and spectrum as well as the ne contamination in the beam at JPARC (Tokai, Japan). It contains three large 2.4 0.9 2.5 m3 TPCs that will measure tracks produced in the fine grained detectors [2]. Each TPC has two 2.4 0.9 m2 readout planes on both sides of the central cathode and each readout plane is paved by 12 bulk-micromegas modules, for an equivalent total surface of 9 m2. The inner and outer sides of a readout plane are shown in Fig. 1. The TPC is operated with Ar(95%)–CF4(3%)–isobutane(2%) gas mixture and ionization electrons are drifted for up to 1m under an electric field of 200 V/cm. After 3 years of R&D, the final design of a module was validated by cosmic rays tests performed on the HARP TPC cage in November 2007. The required performance of a better than 10% momentum resolution at a
momentum of 1 GeV/c, and a better than 10% dE/dx resolution for good particle identification, were achieved [3,4]. The production of the 72 bulk-micromegas, the 124 416 Front-End AFTER Electronics channels [5] and the 3 TPC cages began 1 year ago. The first TPC was equipped with 24 bulk-micromegas modules and Front-End Electronics and tested with cosmics and muon beam at TRIUMF [6]. The 3 TPCs will be commissioned at JPARC at the end of 2009. We report on the production and calibration of the 32 bulk-micromegas modules produced so far.
2. Description and production of the T2K/TPC bulkmicromegas modules The technique for manufacturing all-in-one micromegas detectors, called bulk-micromegas, has been developed by a collaboration between CERN/TS-DEM and IRFU (CEA-Saclay) [7]. The T2K bulk-micromegas is made of a 430 Lines/in., 30 mm thick, 304 L stainless steel woven mesh1 which is laminated on top of the anode Printed Circuit Board covered by a photo-imageable
Tel.: + 33 1 69 08 3454; fax: + 33 1 69 08 3024.
E-mail address: [email protected] 0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.163
1
BOPP, Bachmannweg 21, CH-8046, Zurich, Switzerland (www.bopp.ch).
106
A. Delbart / Nuclear Instruments and Methods in Physics Research A 623 (2010) 105–107
polyimide film. The PCB is 2.2 mm thick and made of four copper layers for anode pads, routing net, grounding and pad-readout connectors. During the lamination, the micromesh is held on an external frame with a tension of 12 N in order to guarantee a good flatness of the micromesh and thereby a uniform micromegas amplification gap of 128 mm. At the end of the process, the detector is cut at its final 34 36 cm2 dimensions. The micromesh is held by a 2 mm coverlay border surrounding the detector’s active area and by 20 736 regularly distributed pillars, maintaining the amplification gap of 128 mm. The pillars, 12 per pad, are cylindrical with a diameter of 0.5 mm [4]. The 6.85 9.65 mm2 pads are arranged in 48 rows of 36 pads each apart from a corner where a two pads equivalent surface is reserved for the micromesh high voltage supply connection from the backside of the PCB (Fig. 2). Ninety-five percent of the surface of a module and more than 85% of the surface of a readout plane is active area.
Fig. 1. A TPC readout plane equipped with 12 micromegas modules and Front-End AFTER Electronics, seen from the inner side of the TPC (left) and seen from the outside of the TPC (right).
These bulk-micromegas MPGD are therefore well suited to pave large detection surfaces with minimal dead zones and minimal drift electric field distortions between modules. The complete production sequence of a T2K/TPC bulk micromegas module is described in Fig. 3. Eight bulk-micromegas are produced per month at CERN/TS-DEM-PMT with several mechanical and electrical quality controls performed at critical steps. Once qualified with a measured global mesh current below 2 nA at 600 V in air, the bulk-micromegas is cut at its final dimensions and equipped with the 24 pad-readout connectors. The bulk-micromegas is then transferred to the T2K/TPC production lab at CERN where it is first glued in class 1000 clean room on a FR5 mechanical stiffener with control of the stiffener’s gasket-tomicromegas’ mesh dimension at 750 mm. This is required to guarantee the proper location and flatness of the micromesh of the 12 modules of a TPC readout plane and thereby a uniform drift electric field. The detector is then inserted into a gas-tight test box filled with dry air and forced to spark by gradually increasing the mesh high-voltage. This way, most of the dusts are burnt, and most of the tiny surface asperities of the micromesh and/or the copper pads are smoothed. This procedure was proved to greatly lower the natural sparking rate of the detector in T2K/TPC gas for a given high-voltage on the micromesh, leading to a safer operation of the detector in the experiment. The quality of the first 32 modules produced is very high: all the detectors sustain up to 900 V in dry-air (70 kV/cm) and four of them have one pad in short-circuit with the mesh (four dead pads over 55 232). The production yield of the anode PCBs is 83% to achieve the stringent Q/C criteria (no electrical defects and PCB thickness within specifications) and the production yield of the bulk-micromegas (including the mesh integration, the final detector’s cutting and the connectors’ soldering) is 4 90%. The last stage of the production is the calibration of the modules on a dedicated automatized test bench. 3. Calibration of the micromegas modules
Fig. 2. T2K/TPC bulk-micromegas module.
Fig. 3. Production sequence of a T2K/TPC bulk-micromegas module.
The purpose of the calibration is to measure the average gain and 5.9 keV resolution with a 370 MBq 55Fe X-ray source for each of the 1726 pads of a module and in the operating conditions of the detector in the T2K/TPC:T2K/TPC gas mixture, AFTER based front-end electronics [5], operating mesh high voltage of 350 V (which corresponds to a micromegas gas gain of around 1700 and a S/N ratio 4200) and 200 V/cm drift electric field. The core of the test bench is a gas chamber designed to define a uniform 4 cm drift electric field and filled with 10 l/h gas flow at 1 mbar above atmospheric pressure. A X–Y motorized holder allows to precisely position the source in front of each pad (Fig. 4). A complete scan of a module is done in around 6 h with 1000 events acquired for each pad. A gain vs mesh high voltage curve ( 320 up to 370 V) is also done for a group of pads in the middle of the module.
Fig. 4.
55
Fe X-ray source calibration test bench.
A. Delbart / Nuclear Instruments and Methods in Physics Research A 623 (2010) 105–107
Fig. 5. Typical gain vs high-voltage curve (left) and
107
55
Fe X-ray source spectrum (right) of a T2K/TPC micromegas detector.
Fig. 6. Typical 2D-map of collected charge (top left) with the corresponding distribution over the 1726 pads (bottom left) and typical 2D-map of r.m.s 5.9 keV resolution (top right) with the corresponding distribution over the 1726 pads (bottom right). Channel (0;30) is a dead electronics channel and the two pads in the bottom right corner are used for mesh HV connection.
Taken from the calibration of the first 32 modules produced so far, a typical 55Fe X-ray source spectrum is shown in Fig. 5 with a 5.9 keV r.m.s resolution of 9%. 2D-maps of collected charge and 5.9 keV energy resolution for each of the 1726 pads of a module are shown in Fig. 6. The typical r.m.s dispersion of collected charge is 2.8% over the whole surface of a detector and the r.m.s dispersion of the average gain of the 32 detectors is 8%. The typical r.m.s dispersion of the 5.9 keV energy resolution is 6% over the whole surface of a detector and the r.m.s dispersion of the average 5.9 keV resolution of the 32 detectors is 3%. Eighty-five percent of the detectors are ‘‘top quality’’ with typical 2D maps shown in Fig. 6, the remaining 15% can present up to 14% 5.9 keV resolution for o 10 pads ( o 1% of the active area). A typical 0.1 spark/hour sparking rate is observed at 350 V mesh voltage in a 1 cm drift chamber. All these figures were corrected for pad capacitance dispersion but not yet for temperature and pressure variations.
4. Conclusion Production of 72 bulk-micromegas modules for the TPCs of the T2K experiment began in May 2008 at CERN and should be completed by summer 2009. The pad per pad calibration of the first 32 modules shows a very good uniformity and reproducibility of performances for both gas gain and 5.9 keV energy resolution. This proves that the bulk-micromegas is becoming a mature technology well suited for high quality and large scale production of large active area MPGDs. References [1] [2] [3] [4] [5] [6] [7]
Y. Itow, et al., hep-ex/0106019. R. Tacik, The T2K fine-grained detectors, these proceedings. J. Bouchez, et al., Nucl. Instr. and Meth. A 574 (2007) 425. S. Anvar, et al., Nucl. Instr. and Meth. A 602 (2009) 415. P. Baron, et al., IEEE Trans. Nucl. Sci. NS-55 (2008) 1744. D. Karlen, Time projection chambers for the T2K experiment, these proceedings. I. Giomataris, et al., Nucl. Instr. and Meth. A 560 (2006) 405.