Pattern Gaseous Detectors Research Articles

The μTPC method: improving the position resolution of neutron detectors based on MPGDs

Due to the 3He crisis, alternatives to the standard neutron detection techniques are becoming urgent. In addition, the instruments of the European Spallation Source (ESS) require advances in the state of the art of neutron detection. The instruments need detectors with excellent neutron detection efficiency, high rate capabilities and unprecedented spatial resolution. The Macromolecular Crystallography instrument (NMX) requires a position resolution in the order of 200 μm over a wide angular range of incoming neutrons. Solid converters in combination with Micro Pattern Gaseous Detectors (MPGDs) are proposed to meet the new requirements. Charged particles rising from the neutron capture have usually ranges larger than several millimetres in gas. This is apparently in contrast with the requirements for the position resolution. In this paper, we present an analysis technique, new in the field of neutron detection, based on the Time Projection Chamber (TPC) concept. Using a standard Single-GEM with the cathode coated with 10B4C, we extract the neutron interaction point with a resolution of better than σ = 200 μm.

Absolute position measurement in a gas time projection chamber via transverse diffusion of drift charge

Time Projection Chambers (TPCs) with charge readout via micro pattern gaseous detectors can provide detailed measurements of charge density distributions. We here report on measurements of alpha particle tracks, using a TPC where the drift charge is amplified with Gas Electron Multipliers and detected with a pixel ASIC. We find that by measuring the 3-D topology of drift charge and fitting for its transverse diffusion, we obtain the absolute position of tracks in the drift direction. For example, we obtain a precision of ~1cm for 0.8cm-long alpha track segments. To our knowledge this is the first demonstration of such a measurement in a gas TPC. This technique has several attractive features: it does not require knowledge of the initial specific ionization, is robust against bias from diffuse charge below detection threshold, and is also robust against high charge densities that saturate the detector response.

Micromegas detectors for the Muon Spectrometer upgrade of the ATLAS experiment

Through the years the Micromegas (MICRO MEsh GAseous Structure) devices have proven to be reliable detectors with excellent space resolution and high rate capability. Large area Micromegas will be employed for the first time in high-energy physics for the Muon Spectrometer upgrade of the ATLAS experiment at the CERN LHC. A total surface of about 150 m2 of the forward regions of the Muon Spectrometer will be equipped with 8 layers of Micromegas modules. Each module covers a surface from 2 to 3 m2 for a total active area of 1200 m2. Together with the small-strips Thin Gap Chambers, they will compose the two New Small Wheels, which will replace the innermost stations of the ATLAS Endcap Muon tracking system in the 2018/19 shutdown. The breakthroughs and developments of this type of Micro Pattern Gas Detector will be reviewed, along with the path towards the construction of the modules, which will take place in several production sites starting in 2015. An overview of the detector performance obtained in the test beam campaigns in recent years at CERN will be also presented.

Front-end electronics and readout system for the ILD TPC

A high resolution TPC is the main option for a central tracking detector at the future International Linear Collider (ILC). It is planned that the MPGD (Micro Pattern Gas Detector) technology will be used for the readout. A Large Prototype TPC at DESY has been used to test the performance of MPGDs in an electron beam of energies up to 6 GeV. The first step in the technology development was to demonstrate that the MPGDs are able to achieve the necessary performance set by the goals of ILC. For this `proof of principle' phase, the ALTRO front-end electronics from the ALICE TPC was used, modified to adapt to MPGD readout. The proof of principle has been verified and at present further improvement of the MPGD technology is going on, using the same readout electronics. The next step is the 'feasibility phase', which aims at producing front-end electronics comparable in size (few mm2) to the readout pads of the TPC. This development work is based on the succeeding SALTRO16 chip, which combines the analogue and digital signal processing in the same chip. This paper summarizes the status of this work and discusses how the experiences made so far can be exploited to improve the final readout electronics.

A dynamic method for charging-up calculations: the case of GEM

The simulation of Micro Pattern Gaseous Detectors (MPGDs) signal response is an important and powerful tool for the design and optimization of such detectors. However, several attempts to exactly simulate the effective gas gain have not been completely successful. Namely, the gain stability over time has not been fully understood.Charging-up of the insulator surfaces have been pointed as one of the responsible for the difference between experimental and Monte Carlo results.This work describes two iterative methods to simulate the charging-up in one MPGD device, the Gas Electron Multiplier (GEM).The first method, which uses a constant step size for avalanches time evolution, is very detailed but slow to compute.The second method instead uses a dynamic step-size that improves the computing time. Good agreement between both methods was achieved.Comparison with experimental results shows that charging-up plays an important role in detectors operation, explaining the time evolution of the gain. However it doesn't seem to be the only responsible for the difference between measurements and Monte Carlo simulations.

Development of a fast neutron imaging system for investigating two-phase flows in nuclear thermal–hydraulic phenomena: A status report

The present paper gives an overview of the status of an ongoing project aiming at the development of a fast neutron imaging system for investigating two-phase flows primarily in the context of nuclear fuel bundle development. Other potential subjects for investigations include steam explosions for severe accident research and liquid metal two-phase flows for Gen IV reactor systems. The project is carried out in the form of a feasibility study that should enable estimation of the ultimate imaging capabilities achievable. The imaging system used in the feasibility study consists of a compact, deuterium–deuterium fusion based neutron generator and dedicated imaging detectors. For the latter two promising concepts are developed in parallel: one is based on an array of plastic scintillators coupled with silicon photomultipliers, the other on a special multi-foil recoil proton converter coupled to a position sensitive charge readout using a micro pattern gas detector.

MPGD R&D Activities in JAPAN

Micro Pattern Gaseous Detector (MPGD) is one of key technology for fine particle tracking and imaging. Some part of recent MPGD R & D activities in Japan are reviewed.

Simulation of gas avalanche in a micro pixel chamber using Garfield++

A micro pixel chamber (μ-PIC), the development of which started in 2000 as a type of a micro pattern gas detector,has a high gas gain greater than 6000 in stable operation, a large detection area of 900 cm2, and a fine position resolution of about 120 μm.However, for its development, simulation verification has not been very useful,because conventional simulations explain only part of the experimental data.On the other hand, some μ-PIC applications require precise understanding of the fluctuation of the gas avalanche and signal waveform for their improvement;therefore, there is a need to update the μ-PIC simulation.Hence, we adopted Garfield++, which is developed for simulating a microscopic avalanche in an effort to explain experimental data.The simulated avalanche size was well consistent with the experimental gas gain.Moreover, we calculated a signal waveform and successfully explained the pulse height and time-over-threshold.These results clearly indicate that the simulation of μ-PIC applications will improveand that Garfield++ simulation will easily facilitate the μ-PIC development.

A comparative numerical study on GEM, MHSP and MSGC

In this work, we have tried to develop a detailed understanding of the physical processes occurring in those variants of Micro Pattern Gas Detectors (MPGDs) that share micro hole and micro strip geometry, like GEM, MHSP and MSGC etc. Some of the important and fundamental characteristics of these detectors such as gain, transparency, efficiency and their operational dependence on different device parameters have been estimated following detailed numerical simulation of the detector dynamics. We have used a relatively new simulation framework developed especially for the MPGDs that combines packages such as GARFIELD, neBEM, MAGBOLTZ and HEED. The results compare closely with the available experimental data. This suggests the efficacy of the framework to model the intricacies of these micro-structured detectors in addition to providing insight into their inherent complex dynamical processes.

MPGD for breast cancer prevention: a high resolution and low dose radiation medical imaging

Early detection of small calcifications in mammograms is considered the best preventive tool of breast cancer. However, existing digital mammography with relatively low radiation skin exposure has limited accessibility and insufficient spatial resolution for small calcification detection. Micro Pattern Gaseous Detectors (MPGD) and associated technologies, increasingly provide new information useful to generate images of microscopic structures and make more accessible cutting edge technology for medical imaging and many other applications. In this work we foresee and develop an application for the new information provided by a MPGD camera in the form of highly controlled images with high dynamical resolution. We present a new Super Detail Image (S-DI) that efficiently profits of this new information provided by the MPGD camera to obtain very high spatial resolution images. Therefore, the method presented in this work shows that the MPGD camera with SD-I, can produce mammograms with the necessary spatial resolution to detect microcalcifications. It would substantially increase efficiency and accessibility of screening mammography to highly improve breast cancer prevention.

Operation of the T2K time projection chambers

The three time projection chambers of the T2K near detector are micro pattern gaseous detectors based on bulk micromegas technology. They have been operated successfully during the first two physics runs of the experiment. Their design, operation, and performance are presented.

RD51, a world-wide collaboration for the development of Micro Pattern Gaseous Detectors

Originally introduced to improve the rate capability of traditional wire chambers, Micro Pattern Gaseous Detectors (MPGD) actually demonstrate many more benefits. Be it for medical and industry imaging, collider experiments or more interestingly in the framework of this conference for the search of rare events, they are the subject of constant research and development in several laboratories over the world. The RD51 collaboration has been coordinating this work since April 2008 and is meant to advance the technological development and application of MPGD. The collaboration is presented and emphasis is put on its latest achievements which do make these devices an attractive option for the detection of low energy rare events: the possibility to instrument large area and to detect UV photons.

A CMOS compatible Microbulk Micromegas-like detector using silicon oxide as spacer material

We present a new Micro Pattern Gaseous Detector (MPGD) fabricated with nonpolymeric materials. The device structure is similar to a Microbulk Micromegas design, consisting of a punctured metal grid supported by a continuous perforated insulating structure. In this detector, the supporting structure is made out of silicon oxide. Devices were tested in He/ iC 4H 10 (80/20) and Ar/ iC 4H 10 (80/20) gas mixtures under 55Fe irradiation. Gas gain of 20,000 and energy resolution below 13% FWHM were achieved. The CMOS compatibility of the fabrication process has been studied in Timepix chips as well as individual 0.13-μm technology CMOS transistors. Complete detectors have been fabricated on top of Timepix chips. In an Ar/ iC 4H 10 (80/20) gas mixture 55Fe decay events were recorded operating the Timepix chip in 2D readout mode.

A lightweight field cage for a large TPC prototype for the ILC

We have developed and constructed the field cage of a prototype Time Projection Chamber for research and development studies for a detector at the International Linear Collider. This prototype has an inner diameter of 72 cm and a length of 61 cm. The design of the field cage wall was optimized for a low material budget of 1.21% of a radiation length and a drift field homogeneity of ΔE/E≲10−4. Since November 2008 the prototype has been part of a comprehensive test beam setup at DESY and used as a test chamber for the development of Micro Pattern Gas Detector based readout devices.

Imaging of high-Z material for nuclear contraband detection with a minimal prototype of a muon tomography station based on GEM detectors

Muon Tomography based on the measurement of multiple scattering of atmospheric cosmic ray muons in matter is a promising technique for detecting heavily shielded high-Z radioactive materials (U, Pu) in cargo or vehicles. The technique uses the deflection of cosmic ray muons in matter to perform tomographic imaging of high-Z material inside a probed volume. A Muon Tomography Station (MTS) requires position-sensitive detectors with high spatial resolution for optimal tracking of incoming and outgoing cosmic ray muons. Micro Pattern Gaseous Detector (MPGD) technologies such as Gas Electron Multiplier (GEM) detectors are excellent candidates for this application. We have built and operated a minimal MTS prototype based on 30cm \times 30cm GEM detectors for probing targets with various Z values inside the MTS volume. We report the first successful detection and imaging of medium-Z and high-Z targets of small volumes (~0.03 liters) using GEM-based Muon Tomography.

Production and calibration of 9 m2 of bulk-micromegas detectors for the readout of the ND280/TPCs of the T2K experiment

The near detector ND280 of the long baseline neutrino experiment T2K (JPARC, Japan) will contain three large 5m3 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 34×36cm2 bulk-micromegas modules of 1726 pads. Production of 72 bulk-micromegas modules, for an equivalent total readout surface of 9m2, 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 5.9keV 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).

Development of high resolution Micro-Pattern Gas Detectors with wide readout pads

A Micro Pattern Gas Detector (MPGD) requires 200 μm wide anode readout pads to achieve ∼ 40 μm resolution. With the development of the new charge dispersion readout concept for MPGDs with a resistive anode, comparable resolution can be achieved with order of magnitude wider pads. We present here an overview and present status of the charge dispersion MPGD readout technology. The development of MPGDs with a resistive anode may permit experiments with large area high resolution tracking requirements to consider using MPGDs which would have been otherwise prohibitive due to excessive readout channel count.

A Time Projection Chamber with triple GEM and pixel readout

Due to many favorable properties it is very attractive to use Micro Pattern Gas Detectors (MPGDs) as gas amplification stages in Time Projection Chambers (TPCs). Especially the high granularity, intrinsic suppression of ion backflow, high rate capability and almost no distortions due to E × B effects are desirable in future particle physics detectors. To fully exploit the potential of combining MPGDs and TPCs the pad size in the readout plane should be adapted to the structure size of the gas amplification stage. The Timepix chip is well suited for the use as readout chip in gaseous detector by providing metalized pads to pick up the charge. We have constructed a test chamber with a triple GEM and Timepix readout and a maximum drift distance of 26 cm. With this setup we have studied the performance of the detector in various operation environments. Different setups for tests with cosmic rays and for tests in high magnetic fields have been realized. In these environments key detector parameters such as spatial resolution have been studied in dependence on different gas mixtures. We have seen strong evidence for observation of individual electrons and a spatial resolution of down to 80 μm has been measured.

Developments of a large area VUV sensitive gas PMT with GEM/μPIC

A new large area UV photon detector with micro pattern gaseous detectors isdeveloped and evaluated.A semitransparent CsI photocathode deposited on a MgF2 window wascombined with 10cm × 10cm GEM and μPIC.Using Ar+C2H6 (10%) gas, we achieved the gas gain of more than 105 which is enough to detect single photoelectron.We, then, irradiated vacuum UV photons (VUV, around 172nm) from the newly developed LaF3(Nd)scintillator to the detector and the single photoelectrons were successfully detected. We also demonstrated the imaging capability of the detector with μPIC readout systems.

New developments in gaseous tracking and imaging detectors

This year we celebrate the 100th birthday of gaseous detectors: Hans Geiger operated the first gas-filled counter in Manchester in 1908. The thin wires, essential for obtaining gas amplification, have been replaced by Micro Pattern Gas Detectors (MPGDs): Micromegas (1995) and GEM (1996). In the GridPix detector, each of the grid holes of a MPGD is equipped with its own electronic readout channel in the form of an active pixel in suitable pixel CMOS chips. By means of chip technology, the grid has been integrated with the chip, forming a monolithic readout device for gas volumes. By applying a protection layer, the chips can be made spark proof. The issue of chamber ageing is addressed. The use of gas as detection material for trackers is compared to Si, and some new developments are set out.