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Abstract:
The purpose of this research is to design and construct a plasma radiation imaging system for fusion devices which is focused on soft X-ray region from about 2 to 15 keV photon energy. The proposed 2D diagnostic system, as opposed to conventional 1D systems, is expected to benefit from tangential field of view and to deliver new data for toroidal phenomena observations. This contribution relates to the introductory development of such 2D system laying out details on the overall design of the detecting unit (based on GEM technology) as well as on its acquisition module. The results cover also the expected photon flux and spectra foreseen for COMPASS-U device, as a first choice for testing and verification. Considerations on working medium and internal structure of the detecting sensor are presented including electrodes configurations and collecting electrode pattern. The preliminary establishments for data acquisition system are presented as well.

Keywords:
Plasma physics, Plasma radiation diagnostics, SXR imaging detector, Micropattern gaseous detectors (MSGC; GEM; THGEM; RETHGEM; MHSP; MICROPIC, MICROMEGAS; InGrid; etc.), Gas electron multiplier, Detector simulations

Abstract:
A detecting system based on the Gas Electron Multiplier (GEM) technology is considered for tokamak plasma radiation monitoring. In order to estimate its capabilities in processing and recording intense photon flux (up to similar to 0.1 MHz/mm(2)), the imaging effectiveness of GEM detectors was tested with different patterned anode planes (i. e., different signal readouts): a simple hexagonal readout structure and three structures with interconnected electrodes (XY square, XY rectangular, and UXV). It was found that under intense photon flux, all the readouts fail to account for a considerable amount of the incoming signals due to mostly photon position determination ambiguity and overlapped signals. Analysis of the signals that can be used to determine photon position and energy unambiguously showed that the UXV readout structure is more effective among the readouts with interconnected electrodes. Along with similar spatial resolution and accuracy, the UXV based layout could be considered as a quite promising base of the interconnected anode electrodes configuration, keeping in mind that the photon rate capability has to be improved for the final application.