Interaction of metal dust adhered on castellated substrates with the ELMy H-mode plasmas of ASDEX-Upgrade

Abstract

Castellated substrates with adhered micron dust have been exposed in the outer ASDEX-Upgrade divertor to ELMy H-mode discharges. Beryllium proxy (chromium, copper) and refractory metal (tungsten, molybdenum) dust has been deposited on the plasma-facing and plasma-shadowed sides of the monoblocks as well as the bottom of the gaps. Interaction with time-averaged transient heat loads up to 5 MW m−2 led to dust remobilization, clustering, melting and wetting-induced coagulation. The amount of dust released in the vessel has been quantified and remobilized dust trajectories inferred. Gaps can efficiently trap locally adhered dust, but dust detaching from adjacent monoblocks does not preferentially move inside the gaps implying that they do not constitute a dust accumulation site. Heat transfer simulations of melting events are also reported taking into account heat constriction due to the finite contact area and the presence of surface roughness.

Resolidification-controlled melt dynamics under fast transient tokamak plasma loads

“…The fluid equations, equations (1), (2), are solved on a 2D geometry along the sample surface imposing a free flow boundary condition at the edge of the melt pool. The heat equation, equation (3), is solved on the full 3D domain that corresponds to the actual sample with surface fluxes due to plasma heating, vaporization, thermal radiation and thermionic emission [17,18]. Latent heat transfer is evaluated with the heat integration method, wherein the phase change enthalpy is counted in each grid point [19].…”

Remobilized dust dynamics and inventory evolution in ITER-like start-up plasmas

“…In particular, the mobilization of larger particles was hindered by supposing a strong inverse scaling between initial radius and velocity, and repeated remobilization events within a single discharge were excluded. The likelihood of such events in concrete fusion plasmas remains an open issue as no direct experimental tests have been attempted, and theoretical approaches are greatly complicated by the stochastic nature of remobilization [21,27,34] as well as the potential effects of numerous phenomena, such as surface roughness [20,21,27,32,33], thermal processes across the dust-wall contact [27,35], or electrostatic perturbations of the plasma sheath due to the presence of particles larger than the local Debye length [20].…”

“…Dust remobilization has been observed experimentally under a wide range of fusion-relevant conditions [20,21,26,27]. Although the intricate details of remobilization phenomena are not thoroughly understood, a consistent description has emerged of their broad features.…”

Observations of dust fragmentations in the Experimental Advanced Superconducting Tokamak

“…2016; Ratynskaia et al. 2016, 2018), the interaction between dust particles and plasma (Laux, Balden & Siemroth 2014; Autricque et al. 2018; Block & Melzer 2019), particle injections and transports (Delzanno & Tang 2014; Lunsford et al.…”

“…In recent years, studies of dust particles in fusion devices have been carried out in many aspects, including the generation and re-deposition of dust particles (Tolias et al 2016;Ratynskaia et al 2016Ratynskaia et al , 2018, the interaction between dust particles and plasma (Laux, Balden & Siemroth 2014;Autricque et al 2018;Block & Melzer 2019), particle injections and transports (Delzanno & Tang 2014;Lunsford et al 2018) and the characteristics of dust particles (Arnas et al 2017;Pardanaud et al 2020;Pan et al 2022). The applications of fast cameras provide an important method for particle and plasma diagnosis (Ratynskaia et al 2011;Shalpegin et al 2015).…”