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WEST (Tungsten Environment in Steady-State Tokamak) will be operating by theend of 2016 as a test bed for the ITER divertor components in long pulseoperation. In this context, radiative cooling of highly ionized impurities liketungsten (W) sputtered from Plasma Facing Components (PFC) into the plasma coreis a critical issue since even small impurity concentrations below 10-4 degradesignificantly plasma performances and can lead to radiative collapse. In theplasma core, tungsten emission is dominant in the Soft X-ray (SXR) range 0.1keV -- 15 keV with complex contributions from line transition, radiativerecombination and Bremsstrahlung emission.This paper presents the recentdevelopment of a synthetic SXR diagnostic using GEM (Gas Electron Multiplier)detectors. This diagnostic will be used on WEST for W transport studies andwill be equipped with two new GEM based poloidal cameras allowing 2Dtomographic reconstructions with spectral resolution in energy bands. Thus onceGEM response to plasma emissivity is characterized thanks to syntheticdiagnostic, it offers new possibilities to disentangle the different SXRcontributions in harsh fusion environments like e.g. WEST or ITER with respectto conventional semiconductor diodes working in current mode. Emitted SXRspectrum from the plasma is modelled thanks to ADAS database from given WESTscenario. The synthetic diagnostic includes Lines of Sight (LoS) etendues ofthe two cameras as well as probability of photoabsorption through filters,photoionization in the detection gas mixture (Ar-CO2), and transport ofelectron avalanches in the gas through GEM foils as computed with Magboltz.Local SXR emissivity is then retrieved from tomographic inversion using aMinimum Fisher Information (MFI) algorithm.

Synthetic SXR diagnostic using GEM detectors on WEST: development in the prospect of tungsten monitoring