Localized divertor leakage measurements using isotopic tungsten sources during edge-localized mode-y H-mode discharges on DIII-D

Unterberg, E.A.; Abrams, T.; Bykov, I.; Donovan, David; Duran, Jonah; Elder, J.D.; Guo, H.Y.; Hollmann, E. M.; Lasnier, C.J.; Leonard, A. W.; Moser, Auna; Nichols, J.H.; Nygren, R.E.; Rudakov, D.L.; Stangeby, P.C.; Thomas, D. M.; Victor, B.S.; Watkins, J. G.; Wampler, W.R.; Zach, Mike P.; Allen, S. L.; Barton, J.L.; Baylor, L. R.; Boedo, J.A.; Briesemeister, A.; Buchenauer, D.; Coburn, Jonathan; Chrobak, C.; Ding, Rui; Ennis, D.A.; Grierson, B.A.; Johnson, Curtis A.; McLean, A.G.; Pétrie, T.W.; Schmitz, O.; Shiraki, D.; Wang, Huiqian; Wilcox, R.S.; Zamperini, Shawn

doi:10.1088/1741-4326/ab537b

Cited by 14 publications

(12 citation statements)

References 52 publications

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“…Moreover, it has long been predicted that the impurity can be accumulated at the crown region of the main SOL [10], and was recently proved by the experimental observation on DIII-D [19,43,44]. But in our simulations, the W accumulation only occurs for the attached regime, as shown in the 2D W density contour plots in figure 8.…”

Section: W Screening In the Main Solsupporting

confidence: 50%

Modelling of tungsten impurity edge transport and screening for different divertor conditions in EAST

Wang

Xu²,

Ding³

et al. 2022

Nucl. Fusion

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Tungsten (W) transport and screening in the edge plasma are investigated for EAST high dissipative divertor conditions. By combining the one-dimensional impurity fluid model (1DImpFM) and the two-point model formatting (2PMF), W screening is proved to be enhanced for high upstream plasma density conditions, mainly because the impurity temperature gradient velocity decreases with the increase of the upstream plasma density. Based on dedicated EAST density ramp-up experiments, two-dimensional simulations of W erosion and transport are carried out for different levels of dissipative divertor conditions by using the SOLPS-DIVIMP code package, and the modeling results are benchmarked with the 1DImpFM analytic model. The prompt-redeposition, the divertor screening, and the main SOL screening are quantitatively analyzed. For detached divertor conditions, the increase of the W ionization length reduces the prompt redeposition rate, but both the divertor screening and SOL screening are reinforced. The 1DImpFM can well interpret the W leakage in the near separatrix region; however, the 2D simulations suggest that the impurity pressure gradient force which is neglected by the 1DImpFM plays an important role, especially in the far-SOL region. With the divertor condition varied from the high-recycling regime to the deep detachment regime, the W source moves from the near strike point region to the far SOL, and thus makes the W transport in the far SOL more important. Therefore, the impurity pressure gradient force cannot be neglected for edge W transport analysis, especially for the detached divertor conditions.

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Section: W Screening In the Main Solsupporting

confidence: 50%

Modelling of tungsten impurity edge transport and screening for different divertor conditions in EAST

Wang

Xu²,

Ding³

et al. 2022

Nucl. Fusion

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“…Despite the higher core leakage fraction, the W density at the OMP separatrix will still be higher at a lower pedestal density due to the higher gross erosion rate (21% higher). Similar trends in erosion and transport were during the DIII-D Metal Rings Campaign, where the probability of W from the toroidally-continuous, W-coated ring located 10 cm outboard of the OSP in the open lower divertor increased by a factor 6 when the pedestal electron density was increased by 50% [51]. Changes to the ionization mean free path and the net force acting on W ions in the far-SOL, among others, were cited in that study as possible reasons for the increase in leakage.…”

Section: Effect Of Upstream Densitysupporting

confidence: 52%

Predicting tungsten erosion and leakage properties for the new V-shaped small angle slot divertor in DIII-D

Sinclair

Maurizio²,

Ma³

et al. 2022

Nucl. Fusion

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Impurity transport modeling of the new tungsten-coated, V-shaped Small Angle Slot (SAS) divertor in the DIII-D tokamak was conducted using the SOLPS-ITER plasma edge code package and the DIVIMP impurity tracking code. The inboard baffle of the current SAS divertor will be shifted closer to the outboard baffle, creating a V-corner at the slot vertex. In addition, the outboard baffle will be coated with 10-15 μm of tungsten (W) for experiments studying high-Z sourcing and leakage in a closed divertor. Modeling of the “SAS-VW” divertor predicts that these changes to the inner baffle will reduce W gross erosion by 40× relative to the existing SAS divertor when the outer strike point is at the V-corner and the ion B×∇B drift is towards the divertor, driven primarily by significant cooling near the slot vertex. Most W erosion in SAS-VW is expected to occur near the slot entrance, which may pose a higher risk to core contamination than W eroded deeper in the slot. Adding a new sheath-based prompt redeposition model outlined in (Guterl J, Bykov I, Ding R and Snyder P 2021 Nucl. Mater. Energy 27 100948) increases the sensitivity of redeposition estimates to near-target plasma conditions and may provide more accurate predictions of net erosion. Moving the outer strike point outboard from the slot vertex ~4 cm onto the W-coated region yielded a 40× increase in the gross erosion rate and a 50% decrease in the core leakage fraction. Thus slight variations in strike point location may counteract the potential benefits of the tightly-baffled V slot on minimizing erosion. This impurity transport modeling provides useful guidance for future experiments on the SAS-VW divertor focused on high-Z erosion/redeposition, scrape-off layer transport, and core leakage.

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“…Modeling of intra-ELM tungsten gross erosion from the continuous toroidal ring [47] with an analytic free-streaming plus recycling model (FSRM) [48,49] is now validated in ITER-relevant mitigated-ELM regimes using pellet pacing and RMPs (figures 11(c) and (d)) [49]. For pellet paced ELMs the FSRM reproduces the observation that the peak intra-ELM W gross erosion is reduced compared with natural ELMs (figure 11(c)).…”

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

confidence: 73%

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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Localized divertor leakage measurements using isotopic tungsten sources during edge-localized mode-y H-mode discharges on DIII-D

Cited by 14 publications

References 52 publications

Modelling of tungsten impurity edge transport and screening for different divertor conditions in EAST

Modelling of tungsten impurity edge transport and screening for different divertor conditions in EAST

Predicting tungsten erosion and leakage properties for the new V-shaped small angle slot divertor in DIII-D

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

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