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The study of Soft X-ray emission can be a source of fundamental information, particularly for what concerns tokamaks and plasma diagnostics, but also in general in the fields of high energy and nuclear physics. Detection systems based on Gas Electron Multipliers (GEM) technology can be of particular use in the context of X-ray analyses, being relatively low cost while maintaining good spatial and temporal resolution and capability to sustain high counting rates (up to MHz/mm2). The development of these new and improved detectors is thus of interest, especially in the research about diagnostic and control of machines for fusion energy. In this work, the performance of a new triple-GEM detector, characterized by an aluminum metallic coating on both layers of the GEM foils, is presented and a comparison is made with the more conventional design employing copper coating. The performances of an aluminum-coated GEM (Al-GEM) detector and of a standard copper-coated GEM (Cu-GEM) detector in revealing quasi-monochromatic X-ray beams coming from different fluorescence materials are compared. The Al-GEM detector is shown to less suffer the issue of unwanted background on the signal caused by the presence of copper inside the detector itself. The suppression of this noise source encourages the use of Al-GEM detectors to perform spectroscopy in harsh environments, such as tokamak machines, where soft X-rays are useful probes to control different plasma properties and parameters. [ABSTRACT FROM AUTHOR]

Abstract: This paper is focused on the soft X-ray tomography system set-up at Tore Supra (DTOMOX) and the recent developments made to get precise information about plasma features from a raw or inverted data. The ultimate aim is not only to use this information in real time for visualisation but also for potential feedback, with a particular emphasis on the optimisation of the reconstruction technique and on simple analysis tools developed for an automatic treatment of these inverted data. Recent progress made on the optimisation of free parameters used for the tomographic inversion will be explained. Finally, future techniques using advanced imaging detector will be presented. In particular, preliminary investigation on the use on Tore Supra of Gas Electron Multiplier (GEM) detector for imaging purposes will be described also including some first observations in situ. [Copyright &y& Elsevier]

A triple gas electron multiplier (GEM) detector has been built and characterized in a collaboration between ENEA, INFN and CEA to develop a soft X-ray imaging diagnostic for magnetic fusion plasmas. It has an active area of 5×5cm2, 128pixels and electronics in counting mode. Since burning plasma experiments will have a very large background of radiation, this prototype has been tested with contemporary X-ray, neutron and gamma irradiation, to study the detection efficiencies, and the discrimination capabilities. The detector has been preliminarily characterized under DD neutron irradiation (2.45MeV) up to 2.2×106 n/s on the detector active area, showing a detection efficiency of about 10−4, while the detection efficiency of X-rays is more than three orders of magnitude higher. The detector has been also tested under DT neutron flux (14MeV) up to 2.8×108 n/s on the whole detector, with a detection efficiency of about 10−5. The calibration of the γ-rays detection has been done by means of a source of 60Co (gamma rays of energy 1.17MeV and 1.33MeV) and the detection efficiency was found of the order of 10−4. Thanks to the adjustable gain of the detector and the discrimination threshold of the electronics, it is possible to minimize the sensitivity to neutrons and gamma, and discriminate the X-ray signals even with very high radiative background. [ABSTRACT FROM AUTHOR]