Dust Studies in DIII-D Tokamak

Abstract

Abstract. Studies of submicron dust using Mie scattering from Nd:YAG lasers and video data of micron to sub-millimeter sized dust on DIII-D tokamak have provided the first data of dust sources and transport during tokamak discharges. During normal operation on DIII-D dust observation rates are low, a few events per discharge or less. The net carbon content of the dust corresponds to a carbon atom density a few orders of magnitude below the core impurity density. Statistical analysis of Mie data collected over months of operation reveal correlation of increased dust rate with increased heating power and impulsive wall loading due to edge localized modes (ELMs) and disruptions. Generation of significant amounts of dust by disruptions is confirmed by the camera data. However, dust production by disruptions alone is insufficient to account for estimated in-vessel dust inventory in DIII-D. After an extended entry vent, thousands of dust particles are observed by cameras in the first 2-3 plasma discharges. Individual particles moving at velocities up to ~300 m/s, breakup of larger particles into pieces, and collisions of particles with walls are observed. After ~70 discharges, dust levels are reduced to a few events per discharge. In order to calibrate diagnostics and benchmark modeling, milligram amounts of micron-sized carbon dust have been injected into DIII-D discharges, leading to the core carbon density increase by a factor of 2-3. Following injection, dust trajectories in the divertor are mostly in the toroidal direction, consistent with the ion drag force. Dust from the injection is observed in the outboard midplane by a fast framing camera. The observed trajectories and velocities of the dust particles are in qualitative agreement with modeling by the 3D DustT code.

Dust Effects on Nucleation Kinetics and Nanoparticle Product Size Distributions: Illustrative Case Study of a Prototype Ir(0)n Transition-Metal Nanoparticle Formation System

“…As noted in the Introduction, even in the best literature we have been able to locate on the effects of microfiltration and the implied dust on nucleation phenomena, direct evidence for the presence of dust (and its precise size, composition, and so on) and then for the removal of dust by microfiltration is lacking. 42 We thought that we should have at least a shot at this challenging problem, and we chose dynamic light scattering (DLS) to start because light scattering has been employed in detecting particles in plasma 51,52 or gases. 53,54 We did so with some trepidation given the expected issues of deconvoluting total light scattering by a wide range of sizes and probably shapes of low levels of broadly heterogeneous dust as well as the omnipresence of dust (e.g., on DLS instrument optics and background air) in any experiments done outside of, ideally, Class 9 Clean Room, experimental conditions.…”

The influence of temperature dynamics and dynamic finite ion Larmor radius effects on seeded high amplitude plasma blobs

“…In magnetised fusion plasmas the exhaust of particles and heat critically determines the lifetime of the plasma facing components. Intermittent outbreaks of spatially localised structures [1,2] may damage the divertor plates and the surrounding wall [3][4][5]. These structures, often referred to as blobs or filaments, are born in the edge in the vicinity of the last closed flux surface (LCFS) and are expelled into the scrape-off layer (SOL).…”

Analyses of dust samples collected in the MAST tokamak

“…But in a first calculation using Rayleigh approximation, the minimum size was estimated to be 55 nm and then 160 nm, using Mie-scattering model and taking into account dust ablation by the laser [31]. Optical imaging with cameras during tokamak operation revealed only the presence of individual big dust particles [32,33]. However, in previous dust analyses, TEM revealed the presence of nanoparticles of $15 nm diameter in Tore Supra [4] and more recent analyses by HRTEM showed, still in this tokamak the presence of onion-like nanoparticles of size as low as 5 nm [17,34].…”