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تسجيل مستخدم جديدSpatial Resolution of a Micromegas-TPC Using the Charge Dispersion Signal
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The Time Projection Chamber (TPC) for the International Linear Collider will need to measure about 200 track points with a resolution close to 100 $mu$m. A Micro Pattern Gas Detector (MPGD) readout TPC could achieve the desired resolution with existing techniques using sub-millimeter width pads at the expense of a large increase in the detector cost and complexity. We have recently applied a new MPGD readout concept of charge dispersion to a prototype GEM-TPC and demonstrated the feasibility of achieving good resolution with pads similar in width to the ones used for the proportional wire TPC. The charge dispersion studies were repeated with a Micromegas TPC amplification stage. We present here our first results on the Micromegas-TPC resolution with charge dispersion. The TPC resolution with the Micromegas readout is compared to our earlier GEM results and to the resolution expected from electron statistics and transverse diffusion in a gaseous TPC.
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The International Linear Collider (ILC) Time Projection Chamber (TPC) transverse space-point resolution goal is 100 microns for all tracks including stiff 90 degree tracks with the full 2 meter drift. A Micro Pattern Gas Detector (MPGD) readout TPC c
an achieve the target resolution with existing techniques using 1 mm or narrower pads at the expense of increased detector cost and complexity. The new MPGD readout technique of charge dispersion can achieve good resolution without resorting to narrow pads. This has been demonstrated previously for 2 mm x 6 mm pads with GEMs and Micromegas in cosmic ray tests and in a KEK beam test in a 1 Tesla magnet. We have recently tested a Micromegas-TPC using the charge dispersion readout concept in a high field super-conducting magnet at DESY. The measured Micromegas gain was found to be constant within 0.5% for magnetic fields up to 5 Tesla. With the strong suppression of transverse diffusion at high magnetic fields, we measure a flat 50 micron resolution at 5 Tesla over the full 15 cm drift length of our prototype TPC.
Since the summer of 2003, a large Micromegas TPC prototype (1000 channels, 50 cm drift, 50 cm diameter) has been operated in a 2T superconducting magnet at Saclay. A description of this apparatus and first results from cosmic ray tests are presented.
Additional measurements using simpler detectors with a laser source, an X-ray gun and radio-active sources are discussed. Drift velocity and gain measurements, electron attachment and aging studies for a Micromegas TPC are presented. In particular, using simulations and measurements, it is shown that an $Argon-CF_4$ mixture is optimal for operation at a future Linear Collider.
Cosmic ray muon has strong penetrating power and no ionizing radiation hazards, which make cosmic ray muon an ideal probe to detect the special nuclear materials (SNM). However, the existing muon tomography experiments have the disadvantages of long
imaging time and poor imaging accuracy, due to the low event rate of muons and small interaction cross section between muons and material nucleus. To optimize the imaging quality and imaging time, high spatial resolution muon tomography facility should be investigated more deeply. Micromegas with its high spatial resolution and large detection area is one of the suitable detectors for the muon tomography facility. In this paper, a high spatial muon tomography prototype was presented. The Micromegas detector was based on thermal bonding technique, which was easy to manufacture and can achieve good performance. A novel multiplexing method base on position encoding was introduced in this research to reduce the channels in an order of magnitude. Then, this paper carried out the research of a general and scalable muon imaging readout system, which employed a discrete architecture of front-end and back-end electronics and can be adapted to different scales of muon tomography experiments. Finally, a tomography prototype system was designed and implemented, including eight Micromegas detectors, four front-end electronics cards and a data acquisition board. Test results showed that this prototype can image objects with 2cm size and distinguish different materials.
NEXT-MM is a general-purpose high pressure (10 bar, $sim25$ l active volume) Xenon-based TPC, read out in charge mode with an 8 cm $times$8 cm-segmented 700 cm$^2$ plane (1152 ch) of the latest microbulk-Micromegas technology. It has been recently co
mmissioned at University of Zaragoza as part of the R&D of the NEXT $0 ubetabeta$ experiment, although the experiments first stage is currently being built based on a SiPM/PMT-readout concept relying on electroluminescence. Around 2 million events were collected during the last months, stemming from the low energy $gamma$-rays emitted by a $^{241}$Am source when interacting with the Xenon gas ($epsilon$ = 26, 30, 59.5 keV). The localized nature of such events above atmospheric pressure, the long drift times, as well as the possibility to determine their production time from the associated $alpha$ particle in coincidence, allow the extraction of primordial properties of the TPC filling gas, namely the drift velocity, diffusion and attachment coefficients. In this work we focus on the little explored combination of Xe and trimethylamine (TMA) for which, in particular, such properties are largely unknown. This gas mixture offers potential advantages over pure Xenon when aimed at Rare Event Searches, mainly due to its Penning characteristics, wave-length shifting properties and reduced diffusion, and it is being actively investigated by our collaboration. The chamber is currently operated at 2.7 bar, as an intermediate step towards the envisaged 10 bar. We report here its performance as well as a first implementation of the calibration procedures that have allowed the extension of the previously reported energy resolution to the whole readout plane (10.6%FWHM@30keV).
We present ion backflow measurements in a Micromegas (MICRO-MEsh GASeous detector) TPC device developed for the next high energy electron-positron linear collider under study and a simple explanation for this backflow. A Micromegas micro-mesh has the
intrinsic property to naturally stop a large fraction of the secondary positive ions created in the avalanche. It is shown that under some workable conditions on the pitch of the mesh and on the gas mixture, the ion feedback is equal to the field ratio (ratio of the drift electric field to the amplification field). Measurements with an intense X-ray source are in good agreement with calculations and simulations. The conclusion is that in the electric field conditions foreseen for the Micromegas TPC (drift and amplification fields respectively equal to 150-200 V/cm and 50-80 kV/cm) the expected ion backflow will be of the order of $2 - 3 x 10^-3$. In addition, measurements have been done in a 2T magnetic field: as expected the ion backflow is not altered by the magnetic field.
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