Characterization of dust particles generated in Thailand Tokamak-1

Thailand Tokamak-1 (TT-1) is the first magnetic confinement fusion device in Thailand and the ASEAN region. During plasma operation, plasma–wall interactions (PWI) inevitably lead to erosion of the 316L stainless-steel vacuum vessel and the boronized first wall, resulting in dust generation and plasma contamination. This work investigates the morphology and elemental composition of dust particles collected from the TT-1 vacuum chamber after plasma campaigns. In this experiment, we carried out a total of 604 discharge operation shots over a period of three months, using 99.999% purity H2 gas as the fuel gas and 99.999% purity He gas for Glow Discharge Cleaning (GDC). Dust was sampled from the inner surface of the vacuum vessel using carbon tape and analyzed by field-emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Four primary dust morphologies were identified: (i) smooth flake-like particles, (ii) grain-crack particles with surface cracking, (iii) granular particles with fine grains distributed across the surface, and (iv) cauliflower-like structures attributed to repeated thermal cycling. EDS analysis revealed that Fe, Cr, and Ni, originating from the 316L stainless-steel wall, are the dominant metallic constituents, together with light elements such as B, C, and O associated with the boronization layer and subsequent oxidation. The presence of B- and C-rich granular dust confirms successful deposition and erosion of the boron coating used for wall conditioning. These results demonstrate that dust generated in TT-1 is a mixture of wall and boronization-layer fragments, which poses potential theoretical risks of plasma impurity accumulation, enhanced radiative losses, and compromised plasma ignition and stability in future high-performance campaigns. The present characterization provides a basis for future studies on dust transport, retention, and mitigation strategies in TT-1 and similar medium-size tokamak devices.