Micro-pattern Gas Detectors Research Articles

Micromesh-selection for the ATLAS New Small Wheel Micromegas detectors

The ATLAS New Small Wheels will be the first major upgrade to an LHC experiment utilizing the Micromegas technology. With an active detection area of 1280 m2 and comprising more than two million channels it is the largest and probably most ambitious system of Micro Pattern Gaseous Detectors (MPGDs) currently under construction. The eponymous component of the Micromegas technology, the micromesh, is the detector's most precise component. Although a wide range of meshes, mesh geometries and parameters can be used to build an operational Micromegas, its properties can affect a range of detector qualities, such as reconstruction efficiency, timing and energy resolution. Conversely, the correct choice of this component will permit a wider range in operation parameters and optimize the detector performance.

Production and quality control of Micromegas anode PCBs for the ATLAS NSW upgrade

To exploit the full discovery potential of the Large Hadron Collider an upgrade towards high luminosity (HL-LHC) is scheduled for 2024–25. Simultaneously to the accelerator, the experiments have to adapt to the expected higher particle rates and detector occupancy. Within the next long shutdown in 2019-20 the innermost end-cap regions of the ATLAS Muon spectrometer will be replaced by the New Small Wheels (NSW) including Micromegas detector modules of several m2 size.The Micromegas readout anode boards, representing the core components of the detector, are manufactured in industry, making the NSW Micromegas the first Micro Pattern Gaseous Detector (MPGD) for a major LHC experiment with a crucial industrial contribution. Production of the up to 2.2 m long boards is a serious challenge for industrialization technology and quality control methods.

Towards spark-proof gaseous pixel detectors

The micro-pattern gaseous pixel detector, is a promising technology for imaging and particle tracking applications. It is a combination of a gas layer acting as detection medium and a CMOS pixelated readout-chip. As a prevention against discharges we deposit a protection layer on the chip and then integrate on top a micromegas-like amplification structure. With this technology we are able to reconstruct 3D track segments of particles passing through the gas thanks to the functionality of the chip. We have turned a Timepix3 chip into a gaseous pixel detector and tested it at the SPS at Cern. The preliminary results are promising and within the expectations. However, the spark protection layer needs further improvement to make reliable detectors. For this reason, we have created a setup for spark-testing. We present the first results obtained from the lab-measurements along with preliminary results from the testbeam.

Detailed 3D Simulation of the GEM-based detector

The operation of Micro Pattern Gaseous Detectors (MPGDs) has often suffered from effects such as distortion of the electric field due to space charge, despite their widespread use in particle-physics and nuclear-physics experiments, astro-particle research, medical imaging, material science etc. To keep distortions due to space-charge at a manageable level, a lower ion feedback is required while maintaining substantial detector gain and good resolution. Thus, a proper optimization of the detector geometry, field configuration and gas mixtures are required to have a higher electron transparency and lower ion backflow. In our work, Garfield simulation framework has been adopted as a tool to evaluate the fundamental features of Gas Electron Multiplier (GEM). Our study begins with the computation of electrostatic field and its variation with different geometrical and electrical parameters using the neBEM toolkit. Different efficient algorithms have been implemented to increase the computational efficiency of the field solver. Finally, ion backflow and electron transparency of single and quadruple GEMs with different geometry and field configurations suitable for the ALICE-TPC, have been studied.

Combination of two Gas Electron Multipliers and a Micromegas as gain elements for a time projection chamber

We measured the properties of a novel combination of two Gas Electron Multipliers with a Micromegas for use as amplification devices in high-rate gaseous time projection chambers. The goal of this design is to minimize the buildup of space charge in the drift volume of such detectors in order to eliminate the standard gating grid and its resultant dead time, while preserving good tracking and particle identification performance. To characterize this micro-pattern gas detector configuration, we measured the positive ion back-flow and energy resolution at various element gains and electric fields, using a variety of gases, and additionally studied crosstalk effects and discharge rates. At a gain of 2000, this configuration achieves an ion back-flow below 0.4% and an energy resolution better than σ/E=12% for 55Fe X-rays.

A prototype scalable readout system for micro-pattern gas detectors**Supported by National Natural Science Foundation of China (11222552)

A scalable readout system (SRS) is designed to provide a general solution for different micro-pattern gas detectors in various applications. The system mainly consists of three kinds of modules: the ASIC card, the adapter card and the front-end card (FEC). The ASIC cards, mounted with particular ASIC chips, are designed for receiving detector signals. The adapter card is in charge of digitizing the output signals from several ASIC cards. The FEC, edged-mounted with the adapter, has field-programmable gate array (FPGA)-based reconfigurable logic and I/O interfaces, allowing users to choose different ASIC cards and adapters for different experiments, which expands the system to various applications. The FEC transfers data through Gigabit Ethernet protocol realized by a TCP processor (SiTCP) IP core in FPGA. By assembling a flexible number of FECs in parallel through Gigabit Ethernet, the readout system can be tailored to specific sizes to adapt to the experiment scales and readout requirements. In this paper, two kinds of multi-channel ASIC chip, VA140 and AGET, are applied to verify the scalability of this SRS architecture. Based on this VA140 or AGET SRS, one FEC covers 8 ASIC (VA140) cards handling 512 detector channels, or 4 ASIC (AGET) cards handling 256 detector channels, respectively. More FECs can be assembled in crates to handle thousands of detector channels.

Quantitative autoradiography of alpha particle emission in geo-materials using the Beaver™ system

In rocks or artificial geo-materials, radioactive isotopes emitting alpha particles are dispersed according to the mineralogy. At hand specimen scale, the achievement of quantitative chemical mapping of these isotopes takes on a specific importance. Knowledge of the distribution of the uranium and thorium series radionuclides is of prime interest to several disciplines, from the geochemistry of uranium deposits, to the dispersion of uranium mill tailings in the biosphere. The disequilibrium of these disintegration chains is also commonly used for dating. However, some prime importance isotopes, such as 226Ra, are complicated to localize in geo-materials. Because of its high specific activity, 226Ra is found in very low concentrations (~ppq), preventing its accurate localization in rock forming minerals.This paper formulates a quantitative answer to the following question: at hand specimen scale, how can alpha emitters in geo-materials be mapped quantitatively? In this study, we tested a new digital autoradiographic method (called the Beaver™) based on a Micro Patterned Gaseous Detector (MPGD) in order to quantitatively map alpha emission at the centimeter scale rock section. Firstly, for two thin sections containing U-bearing minerals at secular equilibrium, we compared the experimental and theoretical alpha count rates, measured by the Beaver™ and calculated from the uranium content, respectively. We found that they are very similar. Secondly, for a set of eight homemade standards made up of a mixture of inactive sand and low-radioactivity mud, we compared the count rates obtained by the Beaver™ and by an alpha spectrometer. The results indicate (i) a linearity between both count rates, and (ii) that the count obtained by the Beaver™ can be estimated from the count obtained by the alpha spectrometry using a factor of 0.82.

Development of a hole-type MPGD with funnel-capillary plate

A new glass capillary plate (CP) has been developed for a hole-type micro-pattern gas detector (MPGD). The developed CP has a funnel structure (funnel-CP) fabricated using a special manufacturing process for a CP. The opening to surface area ratio is 83% for the funnel-CP. A higher ratio is expected to improve the collection efficiency of primary electrons created by X-ray radiations, a higher optical transparency should prove reliable for digital X-ray radiography and cold neutron imaging. Basic performance tests of the hole-type MPGD were carried out using X-ray beams for several gas mixtures based on neon and argon at 1atm. We successfully obtained a gain of up to 1×104, and an energy resolution of 16% for 6keV X-rays. An excellent imaging capability was demonstrated by the X-ray image.

R&D on a new type of micropattern gaseous detector: The Fast Timing Micropattern detector

This contribution introduces a new type of Micropattern Gaseous Detector, the Fast Timing Micropattern (FTM) detector, utilizing fully Resistive WELL structures. The structure of the prototype will be described in detail and the results of the characterization study performed with an X-ray gun will be presented, together with the first results on time resolution based on data collected with muon/pion test beams.

Studies on GEM modules for a Large Prototype TPC for the ILC

The International Linear Collider (ILC) is a future electron–positron collider with centre of mass energy of 500–1000GeV. The International Large Detector (ILD) is one of two detector concepts at the ILC. Its high precision tracking system consists of Silicon sub-detectors and a Time Projection Chamber (TPC) equipped with micro-pattern gas detectors (MPGDs). Within the framework of the LCTPC collaboration, a Large Prototype (LP) TPC has been built as a demonstrator. This prototype has been equipped with Gas Electron Multiplier (GEM) modules and studied with electron beams of energies 1–6GeV at the DESY test beam facility. The performance of the prototype detector and the extrapolation to the ILD TPC is presented here. In addition, ongoing optimisation studies and R&D activities in order to prepare the next GEM module iteration are discussed.

First measurements with new high-resolution gadolinium-GEM neutron detectors

European Spallation Source instruments like the macromolecular diffractometer (NMX) require an excellent neutron detection efficiency, high-rate capabilities, time resolution, and an unprecedented spatial resolution in the order of a few hundred micrometers over a wide angular range of the incoming neutrons. For these instruments solid converters in combination with Micro Pattern Gaseous Detectors (MPGDs) are a promising option. A GEM detector with gadolinium converter was tested on a cold neutron beam at the IFE research reactor in Norway. The μTPC analysis, proven to improve the spatial resolution in the case of 10B converters, is extended to gadolinium based detectors. For the first time, a Gd-GEM was successfully operated to detect neutrons with a measured efficiency of 11.8% at a wavelength of 2 Åand a position resolution better than 250 μm.

A novel method of encoded multiplexing readout for micro-pattern gas detectors

The requirement of a large number of electronic channels poses a big challenge to the further applications of Micro-pattern Gas Detectors (MPGDs). By using the redundancy that at least two neighboring strips record the signal of a particle, a novel method of encoded multiplexing readout for MPGDs is presented in this paper. The method offers a feasible and easily-extensible way of encoding and decoding, and can significantly reduce the number of readout channels. A verification test was carried out on a 5 cm × 5 cm Thick Gas Electron Multiplier (THGEM) detector using a 8 keV Cu X-ray source with 100 μm slit, where 166 strips were read out by 21 encoded readout channels. The test results show good linearity in its position response, and the spatial resolution root-mean-square (RMS) of the test system is about 260 μm. This method has potential to build large area detectors and can be easily adapted to other detectors similar to MPGDs.

Study of a Large Prototype TPC for the ILC using Micro-Pattern Gas Detectors

In the last decade, R&D for detectors for the future International Linear Collider (ILC) has been performed by the community. The International Large Detector (ILD) is one of two detector concepts at the ILC. Its tracking system consists of a Si vertex detector, forward tracking disks and a large volume Time Projection Chamber (TPC). Within the LCTPC collaboration, a Large Prototype (LP) TPC has been built as a demonstrator. Its endplate is able to house up to seven identical modules with Micro-Pattern Gas Detectors (MPGD) amplification. Recently, the LP has been equipped with resistive anode Micromegas (MM) or Gas Electron Multiplier (GEM) modules. Both the MM and GEM technologies have been studied with an electron beam up to 6 GeV in a 1 Tesla solenoid magnet. After introducing the current R&D status, recent results will be presented including field distortions, ion gating and spatial resolution as well as future plans of the LCTPC R&D.

Design and function of an electron mobility spectrometer with a thick gas electron multiplier

The design and function of an electron mobility spectrometer (EMS) including a thick gas electron multiplier (THGEM) is presented. The THGEM was designed to easily be incorporated in an existing EMS to investigate the ability to detect tritium in air using a micropattern gas detector. The THGEM and a collection plate (anode) were installed and the appropriate circuitry was designed and connected to supply the required voltages to the THGEM-EMS. An alpha source (241Am) was used to generate electron-ion pairs within the gas-filled sensitive volume of the EMS. The electrons were used to investigate the THGEM-EMS response as a function of applied voltage to the THGEM and anode. The relative gas-gain and system resolution of the THGEM-EMS were measured at various applied voltage settings. It was observed a potential difference across the THGEM of +420V and potential difference across the induction region of +150V for this EMS setup resulted in the minimum voltage requirements to operate with a stable gain and system resolution. Furthermore, as expected, the gain is strongly affected not only by the potential difference across the THGEM, but also by the applied voltage to the anode and resulting potential difference between the THGEM and anode.

MicroPattern Gaseous Detectors --- New Developments and Applications

MicroPattern Gaseous Detectors --- New Developments and Applications

The μ-RWELL: A compact, spark protected, single amplification-stage MPGD

In this work we present two innovative architectures of resistive MPGDs based on the WELL-amplification concept:– the micro-Resistive WELL (μ-RWELL) is a compact spark-protected single amplification-stage Micro-Pattern Gas Detector (MPGD). The amplification stage, realized with a structure very similar to a GEM foil (called WELL), is embedded through a resistive layer in the readout board. A cathode electrode, defining the gas conversion/drift gap, completes the detector mechanics. The new architecture, showing an excellent space resolution, ~50μm, is a very compact device, robust against discharges and exhibiting a large gain (>104), simple to construct and easy for engineering and then suitable for large area tracking devices as well as digital calorimeters.– the Fast Timing Micro-pattern (FTM): a new device with an architecture based on a stack of several coupled full-resistive layers where drift and multiplication stages (WELL type) alternate in the structure. The signals from each multiplication stage can be read out from any external readout boards through the capacitive couplings, providing a signal with a gain of 104–105. The main advantage of this new device is the improvement of the timing provided by the competition of the ionization processes in the different drift regions, which can be exploited for fast timing at the high luminosity accelerators (e.g. HL-LHC upgrade) as well as for applications like medical imaging.

High granularity tracker based on a Triple-GEMoptically read by a CMOS-based camera

The detection of photons produced during the avalanche development in gas chambers has been the subject of detailed studies in the past. The great progresses achieved in last years in the performance of micro-pattern gas detectors on one side and of photo-sensors on the other provide the possibility of making high granularity and very sensitive particle trackers.In this paper, the results obtained with a triple-GEM structure read-out by a CMOS based sensor are described. The use of an He/CF4 (60/40) gas mixture and a detailed optimization of the electric fields made possible to obtain a very high GEM light yield. About 80 photons per primary electron were detected by the sensor resulting in a very good capability of tracking both muons from cosmic rays and electrons from natural radioactivity.

A micro-pattern gaseous detector for beam monitoring in ion-therapy

A micro-pattern gaseous detector based on gas electron multiplier technology (GEM detector) was developed as a new transmission beam monitor for charged-particle therapy to obtain real-time information about the parameters of a therapeutic beam. Feasibility tests for the GEM detector were performed using an 80-MeV proton beam to evaluate the lateral intensity distributions of a pencil beam and the dose delivered to a target. The beam intensity distributions measured with the GEM detector were in good agreement with those measured with an imaging plate while the charge output from the GEM detector was in proportion to that of a reference dose monitor of an ionization chamber design. These experimental results showed that the GEM detector can be used not only as a beam monitor for the position and two-dimensional intensity distribution but also as a dose monitor. Thus, it is possible to simultaneously measure these beam parameters for beam control in charged-particle therapy using a single GEM-based transmission monitor.

A floating multi-channel picoammeter for micropattern gaseous detector current monitoring

This paper presents a concept of a multiple channel picoammeter suitable for operation at a high voltage. To ensure floating operation, 1kHz readout rate and low battery usage, the picoammeter employs an optical fibre for data transmission. The analogue conditioning section consists of a transimpedance amplifier that is connected to a 16 bit ΣΔ ADC which is integrated into the microcontroller. Simultaneous reception of data sent from multiple picoammeter units is achieved using an FPGA device and a USB interface to the host PC. A prototype with a ±125nA range was constructed. The paper includes a calibration procedure of the prototype and an example of a current leakage test conducted on a 10×10cm2 GEM foil. The resolution achieved by the prototype in a 15min test at 0.5nA bias was 6.5pA FWHM.

Precision tracking with a single gaseous pixel detector

The importance of micro-pattern gaseous detectors has grown over the past few years after successful usage in a large number of applications in physics experiments and medicine. We develop gaseous pixel detectors using micromegas-based amplification structures on top of CMOS pixel readout chips. Using wafer post-processing we add a spark-protection layer and a grid to create an amplification region above the chip, allowing individual electrons released above the grid by the passage of ionising radiation to be recorded. The electron creation point is measured in 3D, using the pixel position for (x, y) and the drift time for z. The track can be reconstructed by fitting a straight line to these points.In this work we have used a pixel-readout-chip which is a small-scale prototype of Timepix3 chip (designed for both silicon and gaseous detection media). This prototype chip has several advantages over the existing Timepix chip, including a faster front-end (pre-amplifier and discriminator) and a faster TDC which reduce timewalk׳s contribution to the z position error. Although the chip is very small (sensitive area of 0.88×0.88mm2), we have built it into a detector with a short drift gap (1.3mm), and measured its tracking performance in an electron beam at DESY. We present the results obtained, which lead to a significant improvement for the resolutions with respect to Timepix-based detectors.