Gas Electron Multiplier Chambers Research Articles

Production status of the JLAB Hall-A GEM and Si [formula omitted] Tracker

We developed and tested a new charged particle tracking system, able to operate in high luminosity experiments, which will be installed at Jefferson Laboratory HallA (VA, USA) for optimally exploit the new 12GeV energy electron beam available at the end of 2013. The tracker is made of six GEM (Gas Electron Multiplier) large chambers and two 10×20cm2 planes of SIlicon microstrip Detectors (SIDs). Each GEM chamber is composed by three 40×50cm2 GEM modules, with two-dimensional strip readout, with expected spatial resolution of about 70μm. The same dedicated acquisition system will be used for both detectors (GEM & SID) for a grand total of more than 50,000 channels. The readout electronics is divided into two parts: the front-end cards (based on the existing APV25 chip), hosted on the detectors periphery and the digitizer, a multi purpose VME-64x/VXS board located far from the high radiation environment. The very same electronics has been adopted by the Olympus experiment (DESY, Hamburg, D) to read out the six GEM chambers of its luminosity monitor. The developed detectors and electronics are now ready for the production, which will last for the next 2 years.

Development of Large Area GEM Chambers

The High Energy Physics group of the University of Texas at Arlington Physics Department has been developing Gas Electron Multiplier (GEM) detectors for use as the sensitive gap detector in digital hadron calorimeters (DHCAL) for the future International Linear Collider. In this study, two kinds of prototype GEM detectors have been tested. One has 30x30 cm 2 active area double GEM structure with a 3 mm drift gap, a 1 mm transfer gap and a 1 mm induction gap. The other one has two 2x2 cm 2 GEM foils in the amplifier stage with a 5 mm drift gap, a 2 mm transfer gap and a 1 mm induction gap. We present characteristics of these detectors obtained using high-energy charged particles, cosmic ray muons and 106 Ru and 55 Fe radioactive sources. From the 55 Fe tests, we observed two well-separated X-ray emission peaks and measured the chamber gain to be over 6500 with a high voltage of 395 V across each GEM electrode. Both the spectra from cosmic rays and the 106 Ru fit well to Landau distributions as expected from minimum ionizing particles. We also present the chamber performance after high dosage exposure to radiation as well as the pressure dependence of the gain and correction factors. Finally, we discuss the quality test results of the first set of large scale GEM foils and discuss progress and future plans for constructing large scale (100cmx100 cm) GEM detectors.

The UA9 experimental layout

The UA9 experimental equipment was installed in the CERN-SPS in March '09 with the aim of investigating crystal assisted collimation in coasting mode. Its basic layout comprises silicon bent crystals acting as primary collimators mounted inside two vacuum vessels. A movable 60 cm long block of tungsten located downstream at about 90 degrees phase advance intercepts the deflected beam.Scintillators, Gas Electron Multiplier chambers and other beam loss monitors measure nuclear loss rates induced by the interaction of the beam halo in the crystal. Two Roman pots installed in the path of the deflected particles are equipped with a Medipix detector to reconstruct the transverse distribution of the impinging beam. Finally UA9 takes advantage of an LHC-collimator prototype installed close to the first Roman pot to help in setting the beam conditions and to analyze the efficiency to deflect the beam. This paper describes in details the hardware installed to study the crystal collimation during 2010.

Development of digital imaging device based on the gas electron multiplier

We fabricated a gas electron multiplier (GEM) for application to digital imaging devices such as X-ray or γ -ray detectors. Sixty-four square ( 3 × 3 mm ) copper pads were used to collect avalanched electron charge clusters from the GEM chamber. A 128-channel charge sensitive preamplifier, which also includes sample/hold amplifiers and a multiplexer, was used as the front end electronics of the readout circuits for data acquisition. With this system, we successfully took a two-dimensional digital image under the irradiation of the 55Fe radiation source.

First Observation of Signals Due to KAERI's 10 MeV Electron Beam by Using GEM Detectors

Department of Physics, University of Texas, Arlington, TX 76019, U.S.A.(Received 12 September 2006)Performance tests of a single channel double Gas Electron multiplier (GEM) detector constructedby the Radiation Detector Development Group of Changwon National University (CNU) and amulti-channel double GEM chamber constructed by the High Energy Physics Group of the Univer-sity of Texas at Arlington was carried out at the Korea Atomic Energy Research Institute (KAERI’s)RF accelerator by using 10-MeV electron beams during May 20 - 26, 2006. In this experiment, weobserved signals by both 10-MeV beam electrons and X-ray photons in the CNU single-channeldouble GEM chamber and in the UTA chamber by using an oscilloscope and photographed wave-forms. By analyzing the chamber output signals on the oscilloscope, computing the number ofX-rays photons produced by bremsstrahlung of the beam electrons in a 2-mm lead plate, calculat-ing the angular distribution of beam electrons caused by multiple scatterings in the lead plate, andestimating the interaction probabilities of X-ray photons in the lead plate, the Ar/CO

A Study on the Edge Enhancement of X-ray Images Generated by a Gas Electron Multiplier Chamber

In this paper, we describe the results of a study on the edge enhancement of X-ray images by using their fuzzy system representation. A set of gray scale X-ray images was generated using the EGS4 computer code. An aluminum plate or a lead plate with three parallel strips taken out has been used as the object with the thickness and the width of the plate, and the gap between the two strips varied. We started with a comparative study on a set of the fuzzy sets for their applicability as the input fuzzy sets for the fuzzy system representation of the gray scale images. Then we describe how the fuzzy system is used to sharpen the edges. Our algorithm is based on adding the magnitude of the gradient not to the pixel value of concern but rather to the nearest neighboring pixel in the direction of the gradient. We show that this algorithm is better in maintaining the spatial resolution of the original image after the edge enhancement.

Radiation hardness and ageing properties of small gap plus GEM chambers

Large size small gap chambers (SGC) equipped with gas electron multiplier (GEM) were exposed to a low-energy hadron beam to characterize their hardness to highly ionizing radiations. During the test, rate and effect of discharges induced by highly ionizing particles were studied as a function of the cathode and GEM voltages. We propose an optimization of the voltages to safely operate the detectors at the largest signal-to-noise ratio. In a second test, the ageing properties of the chambers were measured up to a 5 mC/ cm integrated charge, induced by an X-ray beam. We conclude from the two measurements on the good reliability and possible improvements of the SG plus GEM Chambers for long term use in a harsh radiation environment.