The occurrence and damage of unipolar arcing on fuzzy tungsten

Abstract

This research investigated whether unipolar arcing in the divertor of fusion reactors is a potential cause for enhanced wear of the divertor. It was found that of nano-fuzz growth is sufficient to initiate arcing, mainly depending on the sheath potential drop and electron density. The average mass loss rate induced by the arc was determined from mass loss measurements and found to be consistent with the value estimated from the arc current. The average arc track erosion depth was estimated by using the measured mass loss and damaged surface area and was found to be one tenth of the fuzzy layer thickness. Due to melting of the fuzzy structures the actual depth is larger and some arc tracks occasionally appeared to even reach the bulk beyond the fuzzy layer. The conclusion of this study is therefore that arcing in the divertor of future tokamaks (e.g. ITER) potentially is an important cause for surface damage and plasma pollution.

He-ion induced surface morphology change and nanofuzz growth on hot tungsten surfaces

“…The above peak temperature for nanotendril He release is in excellent agreement with TDS measurements reported by (Gasparyan et al 2016) and (Baldwin et al 2011b). In contrast to the above studies, in which there was no observable mass loss, more aggressive fuzz destruction during unipolar arcing was found to have some accompanying mass loss (Aussems et al 2015).…”

Spectroscopic characterization and imaging of laser- and unipolar arc-induced plasmas

“…7,8 Moreover, since the arcing may take place in fusion experiments, special model experiments have been conducted for a systematic study in which arcing is initiated by plasmas generated by a high-frequency discharge, 9,10 a plasma gun, 11,12 and a laser beam. 4,13,14 What is missing is an investigation into the properties of (unipolar) arc-induced plasma, which requires proper diagnostics. This research uses the transient heat load of a laserpulse to trigger unipolar arcing on fuzzy tungsten and has the aim to spectroscopically characterize the arc-induced plasma.…”

Arc spot grouping: An entanglement of arc spot cells

“…[10][11][12] Recently, with a usage of nanostructured metal (tungsten), several new features of arcing have been revealed. For example, an unipolar arcing was initiated in a controlled way in laboratory plasma devices, [13][14][15] magnetic field dependence of self-affine fractality has been clearly identified, 16 and grouping feature of arcing was observed on the arc trail. 17 The advantage of the usage of the nanostructured medium is likely to be in the changes in some physical properties.…”