Structure and Morphology of the Tungsten-Based Material of the First Wall of a Tokamak Divertor before and after Irradiation with Hydrogen Plasma

Abstract

The results of studying the morphology and structure of the “Tungsten Metal Powder” brand plates (Spetsmetallmaster Group of Companies (SMM GC)) used as protective tiles in the lower divertor of the Globus-M tokamak and subjected to additional processing with the hydrogen plasma of a coaxial accelerator from distances of 50 and 260 mm at 5, 10, and 20 irradiation cycles are described. The morphology and elemental composition of the surface of the plates are determined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The structure of the irradiated surface layer of the plates at an X-ray penetration depth of up to ~1.4 μm is analyzed on the basis of X-ray diffraction (XRD) data using Williamson–Hall profile analysis and size-strain plot methods adapted to take into account the observed pseudo-Voigt type of XRD reflections. The crystal structure of this layer is refined using the Rietveld method. The asymmetry of tungsten reflections after plasma treatment is described by simulation with two (for samples irradiated from a distance of 260 mm) and three (for a distance of 50 mm) crystalline phases of W with the same cubic symmetry, but with a slightly different unit cell parameter and different values of the mean crystallite size and absolute mean value of the microstrain in them.