Double pulse laser-induced breakdown spectroscopy for the analysis of plasma-facing components

Oelmann, J.; Wüst, E.; Sergienko, G.; Brezinsek, S.

doi:10.1088/1402-4896/ac379c

Cited by 7 publications

(2 citation statements)

References 17 publications

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“…This more detailed study will feed into an overall carbon balance in W7-X for OP1.2B, but is out of the scope of the present studies. At this stage we can only refer to recent campaign-integrated information from colorimetric and marker sample analysis after OP1.2B [60] indicating after introduction of boronisations, that the first wall is to a large extent in erosion/deposition balance or shows in specific, mostly shadowed regions, deposition [59,67]. This is inline with the conclusion of the campaignintegrated analysis presented here: the TDU is a net C erosion source.…”

Section: Discussionsupporting

confidence: 62%

Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

et al. 2021

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W7-X completed its plasma operation in hydrogen with island divertor and inertially cooled test divertor unit (TDU) made of graphite. A substantial set of plasma-facing components (PFCs), including in particular marker target elements, were extracted from the W7-X vessel and analysed post-mortem. The analysis provided key information about underlying plasma–surface interactions (PSI) processes, namely erosion, transport, and deposition as well as fuel retention in the graphite components. The net carbon (C) erosion and deposition distribution on the horizontal target (HT) and vertical target (VT) plates were quantified and related to the plasma time in standard divertor configuration with edge transform ι = 5/5, the dominant magnetic configuration of the two operational phases (OP) with TDU. The operation resulted in integrated high net C erosion rate of 2.8 mg s−1 in OP1.2B over 4809 plasma seconds. Boronisations reduced the net erosion on the HT by about a factor 5.4 with respect to OP1.2A owing to the suppression of oxygen (O). In the case of the VT, high peak net C erosion of 11 μm at the strike line was measured during OP1.2B which converts to 2.5 nm s−1 or 1.4 mg s−1 when related to the exposed area of the target plate and the operational time in standard divertor configuration. PSI modelling with ERO2.0 and WallDYN-3D is applied in an interpretative manner and reproduces the net C erosion and deposition pattern at the target plates determined by different post-mortem analysis techniques. This includes also the 13C tracer deposition from the last experiment of OP1.2B with local 13CH4 injection through a magnetic island in one half module. The experimental findings are used to predict the C erosion, transport, and deposition in the next campaigns aiming in long-pulse operation up to 1800 s and utilising the actively cooled carbon-fibre composite (CFC) divertor currently being installed. The CFC divertor has the same geometrical design as the TDU and extrapolation depends mainly on the applied plasma boundary. Extrapolation from campaign averaged information obtained in OP1.2B reveals a net erosion of 7.6 g per 1800 s for a typical W7-X attached divertor plasma in hydrogen.

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Section: Discussionsupporting

confidence: 62%

Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

et al. 2021

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“…Here the limitation of femtosecond LIBS can be observed compared to studies with picosecond lasers that provide a higher pulse energy. In particular, the studies by Oelmann et al (2021) 28 exhibit a depth resolution of 30 nm in a double-pulse configuration. With an enormously shorter heat entry to the sample the heat affection by the laser is smaller and desorption of light particles from higher depths is less likely in relation to ns-LIBS experiments.…”

Section: Discussionmentioning

confidence: 99%

Hydrogen isotope analysis in W-tiles using fs-LIBS

Mittelmann

Touchet

Mao

et al. 2023

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Laser-Induced Breakdown Spectroscopy (LIBS) is a promising technology for in-situ analysis of Plasma-Facing Components in magnetic confinement fusion facilities. It is of major interest to monitor the hydrogen isotope retention i.e. tritium and deuterium over many operation hours to guarantee safety and availability of the future reactor. In our studies we use ultraviolet femtosecond laser pulses to analyze tungsten (W) tiles that were exposed to a deuterium plasma in the linear plasma device PSI-2, which mimics conditions at the first wall. A high-resolution spectrometer is used to detect the Balmer-$$\alpha$$ α transition of the surface from implanted hydrogen isotopes (H and D). We use Calibration Free CF-LIBS to quantify the amount of deuterium stored in W. This proof-of-principle study shows the applicability of femtosecond lasers for the detection of low deuterium concentration as present in first wall material of prevailing fusion experiments.

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