Deuterium and helium outgassing following plasma discharges in WEST: Delayed D outgassing during D-to-He changeover experiments studied with threshold ionization mass spectrometry

Bisson, Régis; Hodille, E.; Gaspar, J.; Douai, D.; Wauters, T.; Gallo, A.; Gunn, J.; Hakola, A.; Loarer, T.; Nouailletas, R.; Moralès, J.; Pégouriè, B.; Reux, C.; Sabot, R.; Tsitrone, E.; Vartanian, S.; Wang, E.; Fedorczak, N.; Brezinsek, S.

doi:10.1016/j.nme.2020.100885

Cited by 7 publications

(9 citation statements)

References 26 publications

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“…A boronisation was performed on the day before the start of the He experiments, but no boronisation was run during the He campaign to avoid strong variations in the vessel wall conditions. After a few shots performed for change over between D and He (typically ~10 shots, see [15] for more details on He to D changeover in WEST), the He/(D 2 +He) ratio, as measured from optical Penning gauge spectroscopy in the exhaust gas, was typically above 90% and up to 95% during the discharge flat top, despite the D prefill. Figure 2 illustrates typical parameters for a shot of the He campaign in terms of plasma current, density and temperature.…”

Section: Plasma Scenario For the He Campaignmentioning

confidence: 99%

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Investigation of plasma wall interactions between tungsten plasma facing components and helium plasmas in the WEST tokamak

Tsitrone¹,

Pégouriè²,

Gunn³

et al. 2022

Nucl. Fusion

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ITER will operate with a tungsten divertor, a material featuring surface morphology changes when exposed to helium plasmas, in particular the formation of the so called tungsten fuzz under specific conditions. Investigating interactions between tungsten plasma facing components and helium plasmas in a tokamak environment is therefore a key point to consolidate predictions for the ITER divertor performance and lifetime. To this end, a dedicated helium campaign was performed in the full tungsten WEST tokamak, cumulating ∼2000 s of repetitive L mode discharges. It is shown that conditions for tungsten fuzz formation, as derived from linear devices experiments (incident helium energy E inc > 20 eV, helium fluence >1024 He/m2, surface temperature T surf > 700 °C), were met in the outer strike point (OSP) area of the inertially cooled tungsten divertor elements of WEST. Preliminary inspection of the components after the campaign did not show visible signs of surface modification, but points to significant net erosion in the OSP area. An extensive post mortem analysis is now ongoing to confirm these first indications. These results underline that the complex balance between erosion/redeposition (in particular linked to impurities) and tungsten fuzz formation needs to be taken into account in tokamak conditions.

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Section: Plasma Scenario For the He Campaignmentioning

confidence: 99%

“…Figure 2), and is not fully recovered during post pulse outgassing up to 30s. He is also seen to outgas more rapidly than D, suggesting different release mechanisms [15]. Local divertor plasma parameters were measured by Langmuir probes, and are shown in Figure 3.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Investigation of plasma wall interactions between tungsten plasma facing components and helium plasmas in the WEST tokamak

Tsitrone¹,

Pégouriè²,

Gunn³

et al. 2022

Nucl. Fusion

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“…Threshold Ionisation Mass Spectrometry was used by Bisson et al to analyse D and He outgassing post-discharge in the full tungsten tokamak WEST. 169 Results included the presentation of the Threshold Ionisation Mass Spectrometry calibration method and consideration for uncertainties due to rapid pressure variations. The He outgassing was significantly faster than D, which may be related to different retention and outgassing from W and W-coated graphite plasma facing components.…”

Section: Inorganic Materialsmentioning

confidence: 99%

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

Carter¹,

Clough

Fisher

et al. 2022

J. Anal. At. Spectrom.

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“…In a real tokamak, the pressure ramp down is limited by the pumping speed of the pumping system and the outgassing from the wall. The pressure decrease is expected to happen in the hundred seconds time scale for tokamaks with metallic walls like JET [43] or WEST [44].…”

Section: Effect Of Realistic Pressure Decreasementioning

confidence: 99%

Modelling tritium adsorption and desorption from tungsten dust particles with a surface kinetic model

et al. 2021

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A kinetic surface model is presented and used to explain the loading and desorption kinetics of tritium retained in micrometre-sized tungsten (W) dust particles. The model describes the sticking of hydrogen isotopes from the gas phase to W surfaces and the desorption from W surfaces. The initial sticking coefficient is set to one and independent of the temperature. The activation energy for desorption depends on the hydrogen coverage of the surface and is parametrised with density functional theory (DFT) calculations for W(100), W(110) and W(111) surfaces. The DFT-parametrised model is successfully compared to experimental results showing that the amount of measured tritium as well as the desorption kinetic can be modelled with only tritium adsorbed on the surface of W dust particles. Then, the model is used to explore possible scenarios to remove the tritium from the W surfaces by exposing the tritiated surfaces to either deuterium and hydrogen. The simulations suggest that it can be possible to remove all the tritium trapped on the W surfaces even at room temperature as soon as the hydrogen or deuterium pressure is higher than the tritium pressure. This gives opportunity to build tritium removal scenarios for ITER.

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Deuterium and helium outgassing following plasma discharges in WEST: Delayed D outgassing during D-to-He changeover experiments studied with threshold ionization mass spectrometry

Cited by 7 publications

References 26 publications

Investigation of plasma wall interactions between tungsten plasma facing components and helium plasmas in the WEST tokamak

Investigation of plasma wall interactions between tungsten plasma facing components and helium plasmas in the WEST tokamak

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

Modelling tritium adsorption and desorption from tungsten dust particles with a surface kinetic model

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