Detailed 3D imaging of Gas Electron Multiplier (GEM) foil hole geometry was realized. Scanning White Light Interferometry was used to examine six topological parameters of GEM foil holes from both sides of the foil. To study the effect of the hole geometry on detector gain, the ANSYS and Garfield ++ software were employed to simulate the GEM detector gain on the basis of SWLI data. In particular, the effective gain in a GEM foil with equally shaped holes was studied. The real GEM foil holes exhibited a 4% lower effective gain and 6% more electrons produced near the exit electrode of the GEM foil than the design anticipated. Our results indicate that the GEM foil hole geometry affects the gain performance of GEM detectors.

/pdf/impact-of-gem-foil-hole-geometry-on-gem-detector-gain-3bvq1sftzr.pdf

Impact of GEM foil hole geometry on GEM detector gain

Detection and Removal of Short-circuits on GEM-foils

.................................................................................................................. 3 Tiivistelmä .............................................................................................................. 4 Acknowledgements ................................................................................................. 5

/pdf/gem-tpc-detectors-for-super-frs-at-fair-2shcd975rh.pdf

Gem-tpc detectors for super-frs at fair

An optical scanning system was commissioned and further developed in the Detector Laboratory of Helsinki Institute of Physics and University of Helsinki. It was designed to automatically scan, perform on-line analysis and to classify the overall quality of GEM-foils especially of the GEM-TPC detectors for Super-FRS at FAIR. The optical scanning system consists of precision positioning table, lighting, optics and operating system with analysis software. It has active scanning area of 95 cm × 95 cm and it can study this area with a resolution of 1441 p/mm. In this paper the performance of the system is studied on different measurement tasks.

Analyzing GEM-foil properties with an optical scanning system

A gas electron multiplier (GEM) is a particle detector used in high-energy physics. Its main component is a thin copper-polymer-copper sandwich that carries O =70  ±  5 µm holes. Quality assurance (QA) is needed to guarantee both long operating life and reading fidelity of the GEM. Absence of layer defects and conformity of the holes to specifications is important. Both hole size and shape influence the detector’s gas multiplication factor and hence affect the collected data. For the scanner the required lateral measurement tolerance is ± 5 µm. We calibrated a high aspect ratio optical scanning system (OSS) to allow ensuring the quality of large GEM foils. For the calibration we microfabricated transfer standards, which were imaged with the OSS and which were compared to corresponding scanning electron microscopy (SEM) images. The calibration fulfilled the ISO/IEC 17025 and UKAS M3003 requirements: the calibration factor was 1.01  ±  0.01, determined at 95% confidence level across a 950  ×  950 mm2 area. The proposed large-scale scanning technique can potentially be valuable in other microfabricated products too.

https://iopscience.iop.org/article/10.1088/0957-0233/25/11/115403/pdf

Calibrating an optical scanner for quality assurance of large area radiation detectors

Deformations can build up in the production stages of the GEM-foils They can affect the performance of the foils and reduce the lifetime of the detector With an optical scanning system that we have obtained and developed to improve our quality control system for GEM-detector construction we can locate and study different types of defects on the GEM-foils We studied standard 100 mm × 100 mm GEM-foils by assembling them as a single-GEM detector with XY-readout and irradiated the areas with defects with X-rays from 55Fe source In this paper we present the results of these measurements

Study of GEM-foil defects with optical scanning system

The PANDA collaboration will build a detector which consists of target and forward spectrometers and aims for studying fundamental questions of hadrons and nuclear physics in interactions of antiprotons with nucleons and nuclei. The detector will be used to identify neutral and charged particles generated within the antiproton-nucleon annihilation processes. The information will be used to perform high-precision tests of strong interactions. A small TPC that will be used for characterization process prior to the development of GEM based TPC for the target spectrometer of PANDA has been designed and built. CAD software was used to create models of all components of the TPC. This complex geometry was parsed into Geant4 detector constructor class. Results of the simulations and tests with the small TPC are presented.

Study of small time projection chamber using Geant4

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Study of GEM-foil defects with optical scanning system

Study of small time projection chamber using Geant4