Impact of ELM control techniques on tungsten sputtering in the DIII-D divertor and extrapolations to ITER

Abrams, T.; Unterberg, E.A.; Rudakov, D. L.; Leonard, A. W.; Schmitz, O.; Shiraki, D.; Baylor, L. R.; Stangeby, P.C.; Thomas, D. M.; Wang, Huiqian

doi:10.1063/1.5089895

Cited by 25 publications

(33 citation statements)

References 53 publications

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“…However, during ELMs, the ion impact energy can be a few keV [11]. The erosion of the tungsten PFCs by ELMs is therefore a concern [36]. On the other hand, the core plasma has a low tolerability to tungsten impurities, as tungsten degrades the core plasma performance [37].…”

Section: Implications For Itermentioning

confidence: 99%

Power deposition behavior of high-density transient hydrogen plasma on tungsten in Magnum-PSI

Li¹,

Morgan²,

Berg-Stolp³

et al. 2021

Plasma Phys. Control. Fusion

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The lifetime of plasma-facing components (PFCs) will have a strong influence on the efficiency and viability of future fusion power plants. However, the PFCs suffer from thermal stresses and physical sputtering induced by edge-localized modes (ELMs). ELMs in future fusion devices are expected to occur with a high plasma density compared to current day devices such that coupling of recycling neutrals and plasma ions will be strong. Because of the scale hierarchy of future fusion devices compared to the present ones, the influence of this coupling is difficult to predict. Here, we investigate the ELM-like hydrogen plasma induced heat loads on tungsten in the linear device Magnum-PSI, producing ∼1 ms plasma pulses with electron densities up to 3.5 × 10 21 m −3 . A combination of time-resolved Thomson scattering and coherent Thomson scattering was used to acquire plasma parameters in front of the target. Moreover, a fast infrared camera coupled to finite element thermal analyses allowed to determine the deposited heat loads on the target. We found a significant inconsistency between the plasma power calculated with a conventional collisionless sheath model and the absorbed power by the target. Moreover, plasma stagnation upstream and plasma cooling downstream were observed during the pulses. The observations are explained based on ionization and elastic collisions between the recycling neutrals and plasma ions. The results highlight the impact of plasma-neutral interaction on the power deposition behavior of ELM-like hydrogen plasma on tungsten.

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Section: Implications For Itermentioning

confidence: 99%

Power deposition behavior of high-density transient hydrogen plasma on tungsten in Magnum-PSI

Li¹,

Morgan²,

Berg-Stolp³

et al. 2021

Plasma Phys. Control. Fusion

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“…the tungsten ring in the lower divertor [47]. Mixed material DIVIMP-WallDYN modeling [45] including E × B drifts is more consistent with the observed redeposition profile (diamonds in figure 11(a)) than modeling that neglects E × B drifts; however, simulations using 60% of the theoretical drifts Reprinted from [48], with the permission of AIP Publishing.…”

Section: Fundamental Plasma Physics Understanding and Model Validatio...mentioning

confidence: 55%

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

et al. 2022

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DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.

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“…ELMs have the effect of transiently increasing the ion impact energy in the divertor (e.g., see [45]), which causes more Si enrichment of the SiC surface (Figure 3) and more Si physical sputtering (Figure 1). The difference between measurement and model diverges at low values of 𝑇𝑇 𝑒𝑒,𝑑𝑑𝑆𝑆𝑑𝑑 , where intra-ELM impurity source begins to dominate over inter-ELM sources [46]. Si physical sputtering yields from SiC are also rather sensitive to the assumed average ion impact angle.…”

Section: Si Erosionmentioning

confidence: 95%

Evaluation of silicon carbide as a divertor armor material in DIII-D H-mode discharges

Abrams¹,

Bringuier²,

Thomas³

et al. 2021

Nucl. Fusion

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Silicon carbide (SiC) represents a promising but largely untested plasma-facing material (PFM) for next-step fusion devices. In this work, an analytic mixed-material erosion model is developed by calculating the physical (via SDTrimSP) and chemical (via empirical scalings) sputtering yield from SiC, Si, and C. The Si content in the near-surface SiC layer is predicted to increase during D plasma bombardment due to more efficient physical and chemical sputtering of C relative to Si. Silicon erosion from SiC thereby occurs primarily from sputtering of the enriched Si layer, rather than directly from the SiC itself. SiC coatings on ATJ graphite, manufactured via chemical vapor deposition, were exposed to repeated H-mode plasma discharges in the DIII-D tokamak to test this model. The qualitative trends from analytic modeling are reproduced by the experimental measurements, obtained via spectroscopic inference using the S/XB method. Quantitatively the model slightly underpredicts measured erosion rates, which is attributed to uncertainties in the ion impact angle distribution, as well as the effect of edge-localized modes. After exposure, minimal changes to the macroscopic or microscopic surface morphology of the SiC coatings were observed. Compositional analysis reveals Si enrichment of about 10%, in line with expectations from the erosion model. Extrapolating to a DEMO-type device, an order-of-magnitude decrease in impurity sourcing, and up to a factor of 2 decrease in impurity radiation, is expected with SiC walls, relative to graphite, if low C plasma impurity content can be achieved. These favorable erosion properties motivate further investigations of SiC as a low-Z, non-metallic PFM.

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Impact of ELM control techniques on tungsten sputtering in the DIII-D divertor and extrapolations to ITER

Cited by 25 publications

References 53 publications

Power deposition behavior of high-density transient hydrogen plasma on tungsten in Magnum-PSI

Power deposition behavior of high-density transient hydrogen plasma on tungsten in Magnum-PSI

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

Evaluation of silicon carbide as a divertor armor material in DIII-D H-mode discharges

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