Tungsten erosion by arcs in ASDEX upgrade

Rohde, V.; Endstrasser, N.; Toussaint, U. von; Balden, M.; Lunt, T.; Neu, R.; Hakola, A.; Bucalossi, J.

doi:10.1016/j.jnucmat.2010.11.045

Cited by 58 publications

(26 citation statements)

References 8 publications

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“…4 The existence of the unipolar arc has been confirmed phenomenologically by erosion craters found in numerous fusion devices: JT-60U, LHD, 5 DIII-D, 6 and ASDEX Upgrade. 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.…”

Section: à3mentioning

confidence: 99%

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

Aussems

Nishijima

Brandt

et al. 2014

Journal of Applied Physics

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Characteristics of plasma properties in an ablative pulsed plasma thruster Phys. Plasmas 20, 033503 (2013) Tungsten plasmas induced by unipolar arcs were investigated using optical emission spectroscopy and imaging, and compared with laser-induced tungsten plasmas. The unipolar arcs were initiated in the linear-plasma simulator PISCES-A at UCSD under fusion relevant conditions. The electron temperature and density of the unipolar arc plasmas were in the range 0.5-0.7 eV and 0.7-2.0 Â 10 20 m À3, respectively, and increased with increasing negative bias voltage, but did not correlate with the surface temperature. In comparison, the electron temperature and density of the laser-induced plasmas were in the range 0.6-1.4 eV and 7 Â 10

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Section: à3mentioning

confidence: 99%

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

Aussems

Nishijima

Brandt

et al. 2014

Journal of Applied Physics

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“…If arcs are burning at the first wall liquid particles as a typical product of arc erosion will be ejected from the typical craters (figure 1) into the SOL [1,2,3,4,5]. During its flight through the plasma the particles will be evaporated [6,7] introducing wall material into the SOL and, eventually, some may even cross the LCFS thereby injecting a fraction of the impurity material into the confined central plasma column.…”

Section: Introductionmentioning

confidence: 99%

Modification of arc emitted W particles in a model scrape-off layer plasma

Laux

Balden

Siemroth³

2014

Phys. Scr.

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Abstract. In fusion machines (like e.g. ASDEX Upgrade and JET) equipped with W-coated plasma facing components (PFCs) arc tracks are observed post-mortem and W-particles are identified as a component of the dust. Results from laboratory arcing of W-coated PFC-material concerning the size, velocity, and direction of macro-particles are combined with model calculations of the heating, cooling, and evaporation of W particles flying through a simplified scrape-off layer (SOL) plasma to assess the role of arc produced particles as a source of W-impurities. W atoms or ions eroded from a macro-particle flying across the SOL plasma are not subject to prompt re-deposition onto a PFC. Therefore, macro-particles constitute an essential source of W in the SOL and even may result in an impurity input into the region of confined plasma if the particle succeeds to path the SOL and cross the last closed flux surface (LCFS). The main result of the modelling is that a W-particle from the large-size end of the distribution obtained in laboratory arcing and having a typical velocity (also known from laboratory experiment) is able to pass a SOL of 10cm thickness filled with a realistic plasma and, finally, inject a certain amount of Wmaterial into the confined plasma region.

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“…The origin of the W spheroids is proposed to be arcing, which ejects molten tungsten solidifying in spheroid shape [47,64 ]. Probably, the pores are formed during the solidification process of the molten W droplet and the nucleation of several grains.…”

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confidence: 99%

Collection strategy, inner morphology, and size distribution of dust particles in ASDEX Upgrade

et al. 2014

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Abstract.The dust collection and analysis strategy in ASDEX Upgrade (AUG) is described. During five consecutive operation campaigns (2007)(2008)(2009)(2010)(2011), Si collectors were installed, which were supported by filtered vacuum sampling and collection with adhesive tapes in 2009. The outer and inner morphology (e.g. shape) and elemental composition of the collected particles were analysed by scanning electron microscopy. The majority of the ~50000 analysed particles on the Si collectors of campaign 2009 contain tungsten -the plasma-facing material in AUG -and show basically two different types of outer appearance: spheroids and irregularly shaped particles. By far most of the W-dominated spheroids consist of a solid W core, i.e., solidified W droplets. A part of these particles is coated with low Z material; a process which seems to happen presumably in the far scrape off layer plasma. In addition, some conglomerates of B, C, and W appear as spherical particles after their contact with plasma. By far most of the particles classified as B-, C-, and W-dominated irregularly shaped particles consist of the same conglomerate with varying fraction of embedded W in the B-C matrix and some porosity, which can exceed 50%. The fragile structures of many conglomerates confirm the absence of intensive plasma contact. Both the ablation and mobilization of conglomerate material and the production of W droplets are proposed to be triggered by arcing. The size distribution of each dust particle class is best described by a lognormal distribution allowing an extrapolation of the dust volume and surface area. The maximum in this distribution is observed above the resolution limit of 0.28 µm only for the W-dominated spheroids, at around 1 µm. The amount of W-containing dust is extrapolated to be less than 300 mg on the horizontal areas of AUG.

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Tungsten erosion by arcs in ASDEX upgrade

Cited by 58 publications

References 8 publications

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

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

Modification of arc emitted W particles in a model scrape-off layer plasma

Collection strategy, inner morphology, and size distribution of dust particles in ASDEX Upgrade

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