N1D4  Gaseous Detectors: R&D I

Monday, Nov. 2  16:30-18:10  Pacific Salon 1&2

Session Chair:  Silvia Dalla Torre, INFN Trieste, Italy; Graham Smith, Brookhaven National Laboratory, United States

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(16:30) N1D4-1, The Pixel-TPC: a Feasibility Study

M. Lupberger

University of Bonn, Bonn, Germany

On behalf of the LCTPC Collaboration
The idea to combine micro-pattern gaseous detectors (MPGDs) with a pixelised readout was born more than 10 years ago. Since about 5 years, the InGrid, an ASIC including a Micromegas is available. It can detect single electrons with high granularity. This feature would also improve the performance of Time Projection Chambers (TPCs). However, the endplate of such detectors measures several square meters compared to an InGrid with 1.4 cm × 1.4 cm. Many of these devices have to be combined to increase the sensitive area.
In context of the International Large Detector (ILD) at the ILC, new technologies based on MPGDs are tested as TPC readout. The ILD is designed to consist of modules with a size of about 400 cm2. The goal of the project presented here was, to demonstrate that it is possible to build and operate a module with about 100 InGrid chips. For test beams, the LCTPC collaboration provides a TPC prototype at DESY that can hold those modules.
For the Timepix, which is the ASIC of the InGrid, a new readout system had to be designed. The Scalable Readout System from the RD51 collaboration at CERN was chosen as basis. Additional electronics, FPGA firmware and data acquisition software had to be developed to implement the Timepix chip.
The module construction was done in two stages. First, an 8-InGrid module as tested as a proof of principle and for a review of the design. Field distortions between the InGrids, cooling and powering were investigated.
Finally, the novel type of gaseous detector, called Pixel-TPC, was operated for the first time at a test beam in spring 2015. It consisted of three modules with in total 160 InGrids. 1.5 million track with a length of about 60 cm were recorded in the TPC with 10.5 million channels.

The presentation will mainly focus on the technological development of this new detector type. In addition, analyses concerning the data quality and TPC performance will be shown.

(16:50) N1D4-2, Imaging Demonstration of a Glass Gas Electron Multiplier with Analogue Charge Readout

Y. Mitsuya1, P. Thuiner2,3, E. Oliveri3, F. Resnati3, M. V. Stenis3, T. Fujiwara4, H. Takahashi1, C. Streli2, L. Ropelewski3

1The University of Tokyo, Tokyo, Japan
2Vienna University of Technology, Vienna, Austria
3European Organization for Nuclear Research (CERN), Geneva, Switzerland
4National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
We have developed a Glass Gaseous Electron Multiplier (Glass GEM, G-GEM), which is composed of two copper electrodes separated by a photoetchable glass substrate with holes arranged in a honeycomb pattern. In this paper we report the result of imaging with a G-GEM combined with a 2D analogue charge readout. We used a crystallized photoetchable glass (PEG3C) as the G-GEM substrate. A precise X-ray image of a small mammal was successfully obtained with position resolution of less than 150 micrometers in standard deviation.

(17:10) N1D4-3, Particle Tracking with GEMPix, a Timepix Based Triple GEM Detector

S. P. George1, F. Murtas1, J. Alozy1, A. Curioni1, A. B. Rozenfeld2, M. Silari1

1CERN, 1211 Geneva, Switzerland
2Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia
This paper details the response of a triple GEM detector with a 55 µm pitch pixelated ASIC (the Timepix) for readout. The detector is operated as a micro TPC with 9.5 cm3 (3×3×1.2 cm3) sensitive volume and characterized with a mixed beam of 120 GeV protons and positive pions. A process for reconstruction of incident particle tracks from individual ionization clusters is described and scans of the gain and drift fields are performed. The drift velocity is measured and used to construct 3D paths of the tracks in the detector. The angular resolution of the measured tracks is characterized to be between 1 and 7 degrees depending on the angle of the incident beam, the spatial resolution was measured to be 170 µm. Also, the readout was operated in a mixed mode where some pixels measure drift time and others charge, in order to simultaneously measure the drift time and charge deposition. The charge deposition spectrum is compared to a Geant4 simulation and found to match well. The charge cloud size as a function of interaction depth is investigated. Future improvements to the device and its potential use as a ‘tracking microdosimeter’ are discussed.

(17:30) N1D4-4, Scintillating Glass GEM Detector for High Resolution X-Ray Imaging and CT

T. Fujiwara1, Y. Mitsuya2, H. Takahashi2, T. Yanagida3, H. Toyokawa1

1National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
2Department of Nuclear Engineering and Management, The University of Tokyo, Bunkyo, Tokyo, Japan
3Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara, Japan
A novel radiation imaging gaseous detector has been successfully developed and 3D computed tomography (CT) is successfully demonstrated. The imaging system consists of a chamber filled with Ar/CF4 scintillating gas mixture, inside of which Glass GEM (G-GEM) is mounted for gas multiplication. In this system electrons are generated by the reaction between X-rays and the gas, and visible photons by excited Ar/CF4 gas molecules during the gas electron multiplication process in the G-GEM holes. These photons are detected by a mirror-lens-CCD-camera system and a radiograph is formed. Here, we report on the scintillation properties of G-GEM and the results of using it as a digital X-ray imager with a large sensitive area. Since the imaging system is based on a gaseous detector, it shows high sensitivity to low-energy X-rays, which results in a high contrast radiograph for elements with low atomic numbers. In addition, the combination of G-GEM (280 µm pitch precise holes) and a 300,000 pixel CCD sensor enables high spatial resolution. Moreover, a high gas gain of G-GEM enables rapid imaging. Successful operation of G-GEM with a scintillating gas and a mirror-lens-CCD-camera system has enabled us to realize a novel radiation imaging device for digital X-ray imaging and we successfully demonstrated 3D X-ray CT.

(17:50) N1D4-5, Effects of High Charge Densities in Multi-GEM Detectors

F. Resnati1, S. Franchino1, D. Gonzalez Diaz1, R. Hall-Wilton2, H. Muller1, E. Oliveri1, D. Pfeiffer1,2, L. Ropelewski1, M. Van Stenis1, C. Streli3, P. Thuiner1,3, R. Veenhof1

1CERN, Geneva, Switzerland
2ESS, Lund, Sweden
3TUW, Wien, Austria
One of the key features of Gaseous Electron Multipliers (GEMs) is their capability to well cope with high particle fluxes. For this reason, GEMs will be installed in the forward muon detector system of CMS, and as amplification device in the ALICE TPC. For the first time, we present a study of the intrinsic limits of GEM detectors when exposed to very large particle fluxes or operated at very large gains, and we give an interpretation of the results. The observed variations of the gain, of the ion back-flow, and of the pulse height spectra are fully explained in terms of the effects of the spatial distribution of positive ions and their movement. As a function of the particle flux, the dynamic equilibrium of creation and evacuation of ions results in a space charge which distorts the electric field such that the effective gain first increases and then decreases. This behaviour is expected to be common to all multi-stage amplification devices where the efficiency of transferring the electrons from one stage to the next is not 100%. At very high gains, the ions produced within each avalanche instantaneously modify the electric field such that its growth is quenched the larger the avalanche is. These behaviours are well reproduced by computations done with COMSOL Multiphysics, which allows to dynamically compute the electric field in the presence of charges, as well as the amplification and transport of the charges themselves under the influence of the electric field. The predictive capabilities of our model can be used in specific applications for the detector optimisation. The impact of a detailed study of the detector in extreme conditions is multiple: it clarifies some detector behaviours observed for several years, it defines intrinsic limits of the GEM technology, and it suggests possible ways to extend them.