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Register a new userBeam Performance of Tracking Detectors with Industrially Produced GEM Foils
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Three Gas-Electron-Multiplier tracking detectors with an active area of 10 cm x 10 cm and a two-dimensional, laser-etched orthogonal strip readout have been tested extensively in particle beams at the Meson Test Beam Facility at Fermilab. These detectors used GEM foils produced by Tech-Etch, Inc. They showed an efficiency in excess of 95% and spatial resolution better than 70 um. The influence of the angle of incidence of particles on efficiency and spatial resolution was studied in detail.
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The planned tracking upgrade of the STAR experiment at RHIC includes a large-area GEM tracker used to determine the charge sign of electrons and positrons produced from W+(-) decays. For such a large-scale project commercial availability of GEM foils is necessary. We report first results obtained with a triple GEM detector using GEM foils produced by Tech-Etch Inc. of Plymouth, MA, USA. Measurements of gain uniformity, long-term stability as well as measurements of the energy resolution for X-Rays are compared to results obtained with an identical detector using GEM foils produced at CERN. A quality assurance procedure based on optical tests using an automated high-resolution scanner has been established, allowing a study of the correlation of the observed behavior of the detector and the geometrical properties of the GEM foils. Detectors based on Tech-Etch and CERN produced foils both show good uniformity of the gain over the active area and stable gain after an initial charge-up period, making them well suited for precision tracking applications.
Many experiments are currently using or proposing to use large area GEM foils in their detectors, which is creating a need for commercially available GEM foils. Currently CERN is the only main distributor of large GEM foils, however with the growing interest in GEM technology keeping up with the increasing demand for GEMs will be difficult. Thus the commercialization of GEMs up to 50 $times$ 50 cm$^2$ has been established by Tech-Etch Inc. of Plymouth, MA, USA using the single-mask technique. The electrical performance and optical quality of the single-mask GEM foils have been found to be on par with those produced by CERN. The next critical step towards validating the Tech-Etch single-mask GEM foils is to test their performance under physics conditions. These measurements will allow us to quantify and compare the gain and efficiency of the detector to other triple-GEM detectors. This will be done by constructing several single-mask triple-GEM detectors, using foils manufactured by Tech-Etch, which follow the design used by the STAR Forward GEM Tracker (FGT). These detectors will investigate ways in which to further decrease the material budget and increase the efficiency of the detector by incorporating perforated Kapton spacer rings rather than G10 spacing grids to reduce the dead area of the detector. The materials and tooling needed to assemble the triple-GEM detectors have been acquired. The GEM foils have been electrically tested, and a handful have been optically scanned. We found these results to be consistent with GEM foils produced by CERN. With the success of these initial tests, construction of the triple-GEM detectors is now under way.
Fiber Bragg Grating (FBG) sensors have been so far mainly used in high energy physics (HEP) as high precision positioning and re-positioning sensors and as low cost, easy to mount, radiation hard and low space- consuming temperature and humidity devices. FBGs are also commonly used for very precise strain measurements. In this work we present a novel use of FBGs as flatness and mechanical tensioning sensors applied to the wide Gas Electron Multiplier (GEM) foils of the GE1/1 chambers of the Compact Muon Solenoid (CMS) experiment at Large Hadron Collider (LHC) of CERN. A network of FBG sensors has been used to determine the optimal mechanical tension applied and to characterize the mechanical stress applied to the foils. The preliminary results of the test performed on a full size GE1/1 final prototype and possible future developments will be discussed.
An analysis software was developed for the high aspect ratio optical scanning system in the Detec- tor Laboratory of the University of Helsinki and the Helsinki Institute of Physics. The system is used e.g. in the quality assurance of the GEM-TPC detectors being developed for the beam diagnostics system of the SuperFRS at future FAIR facility. The software was tested by analyzing five CERN standard GEM foils scanned with the optical scanning system. The measurement uncertainty of the diameter of the GEM holes and the pitch of the hole pattern was found to be 0.5 {mu}m and 0.3 {mu}m, respectively. The software design and the performance are discussed. The correlation between the GEM hole size distribution and the corresponding gain variation was studied by comparing them against a detailed gain mapping of a foil and a set of six lower precision control measurements. It can be seen that a qualitative estimation of the behavior of the local variation in gain across the GEM foil can be made based on the measured sizes of the outer and inner holes.
Many experiments are currently using or proposing to use large area GEM foils in their detectors, which is creating a need for commercially available GEM foils. Currently CERN is the only main distributor of large GEM foils, however with the growing interest in GEM technology keeping up with the increasing demand for GEMs will be difficult. We present here an update on the assembly and testing of triple-GEM tracking detectors utilizing single-masked $40 times 40$ cm$^2$ commercial GEM foils produced by Tech-Etch. The triple-GEM detectors will allow us to characterize the overall quality of these Tech-Etch foils through gain, efficiency, and energy resolution measurements. This will be done by constructing four single-mask triple-GEM detectors, using foils manufactured by Tech-Etch, which follow the design used by the STAR Forward GEM Tracker (FGT). The stack is formed by gluing the foils to the frames and then gluing the frames together. The stack also includes a Tech-Etch produced high voltage foil and a 2D $r-phi$ readout foil. While one of the four triple-GEM detectors will be built identically to the STAR FGT, the other three will investigate ways in which to further decrease the material budget and increase the efficiency of the detector by incorporating perforated Kapton spacer rings rather than G10 spacing grids to reduce the dead area of the detector.
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