Geometrical characterization, chemical composition analysis, and deuterium retention study on micro-particles used for powder injection experiments in tokamak and stellarator plasmas*

Impurity powder dropper (IPD) has been used to inject microparticles of B, Si, C, and Li into fusion plasmas for in-situ and real-time wall coating and better plasma control and confinement [1]. Dust particles have been also formed in fusion reactors due to erosion and are thought to be a major issue of tritium trapping in future plasma devices [2]. In this study, we analyzed properties of IPD powders of B, B₄C, BN, C, Si, etc., such as size and shape distributions using scanning electron microscopy (SEM) and confocal microscopy, and chemical compositions using energy-dispersive X-ray spectroscopy (EDS). In an ultrahigh vacuum chamber, we installed a new powder sample manipulator which enable us to perform D ion/atom irradiations followed by temperature programmed desorption (TPD) to quantify the retained deuterium and deuterium desorption temperature in powder samples, which are supposed to emulate dust particles formed in fusion reactors. The manipulator was utilized to ramp up the temperatures up to 1100 K to study D desorption from B and B-C targets. We also utilized a Monte Carlo micro-patterning and roughness (MPR) code to simulate the ion irradiation patterns and area on the particles using 3D geometrical data obtained by confocal microscopy as an input. [1] A. Bortolon, Nucl. Fusion 60, 126010 (2020) [2] S. Ratynskaia et al., Rev. Mod. Plasma Phys. 6:20 (2022)