GEM based plasma radiation diagnostics development: design aspects affecting its performance

The advanced Soft X-ray (SXR) diagnostics setup devoted to studies of the SXR plasma emissivity focusing on the energy range of tungsten emission lines is at the moment a highly relevant and important for ITER/DEMO as W became a plasma-facing material and, therefore, plasma contamination by W and W transport in the plasma must be understood and monitored. The Gas Electron Multiplier (GEM) based SXR radiation detecting system under development by our group with a spatial and energy-resolved photon detecting chamber may become such a diagnostic setup; however, many physical, technical and technological aspects must be taken into consideration. This work presents the results of preliminary tests and simulations of the research into the optimal design of the detector’s internal chamber. The study of the effect of electrodes alignment allowed choosing the gap distances which maximize electron transmission. The study of the influence of different GEM foils on the properties and distribution of the electron avalanche as well as the effect of the high rate photon flux on GEM foil performance was performed. Finally, the optimal readout structure design was identified suitable to collect a total formed charge effectively.