ELM and inter-ELM heat and particle flux to a secondary divertor in the DIII-D tokamak

Perillo, R.; Boedo, J. A.; Lasnier, C.J.; Rudakov, D.L.; Osborne, T.H.; Watkins, J.G.

doi:10.1088/1741-4326/ac0f38

Cited by 4 publications

(2 citation statements)

References 51 publications

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“…Finally, the PLM model is benchmarked with IRTV data of attached type-I ELMs at the secondary outer divertor in unbalanced QDN (or 'weak' USN) configurations. Details on the design of this experiment can be found in [68]. In short, shots have ∼identical plasma parameters but dR sep (i.e.…”

Section: Plm Simulations Of Type-i Elms To An Attached Secondary Dive...mentioning

confidence: 99%

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Perillo,

Boedo,

Lasnier

et al. 2023

Nucl. Fusion

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Type-I and type-II Edge-Localized-Modes (ELMs) heat flux profiles measured at the DIII-D divertor feature a peak in the vicinity of the strike-point and a plateau in the scrape-off-layer (SOL), which extends to the first wall. The plateau is present in attached and detached divertors and it is found to originate with plasma bursts upstream in the SOL. The integrated ELM heat flux is distributed at ~65% in the peak and ~35% in this plateau. The Parallel Loss Model (PLM), currently used at ITER to predict power loads to the walls, is benchmarked using these results in the primary and secondary divertors with unprecedented constraints using experimental input data for ELM size, radial velocity, energy, electron temperature and density, heat flux footprints and number of filaments. The model can reproduce the experimental near-SOL peak within ~20%, but cannot match the SOL plateau. Employing a two-component approach for the ELM radial velocity, as guided by intermittent data, the full radial heat flux profile can be well matched. The ELM-averaged radial velocity at the separatrix, which explains profile widening, increases from ~0.2 km/s in attached to ~0.8 km/s in detached scenarios, as the ELM filaments’ path becomes electrically disconnected from the sheath at the target.The results presented here indicate filaments fragmentation as a possible mechanism for ELM transport to the far-SOL and provide evidence on the beneficial role of detachment to mitigate ELM flux in the divertor far-SOL. However, these findings imply that wall regions far from the strike points in future machines should be designed to withstand significant heat flux, even for small-ELM regimes. 

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Section: Plm Simulations Of Type-i Elms To An Attached Secondary Dive...mentioning

confidence: 99%

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Perillo,

Boedo,

Lasnier

et al. 2023

Nucl. Fusion

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“…This may account for some portion of the missing heat flux from pellet-triggered ELMs shown in figure 16. Recent studies in DIII-D have shown that significant ELM-induced heat flux extends to the secondary divertor when there is a secondary X-point, even when the separation between the two X-point separatrices is quite large [46]. If devices are expected to withstand operation with ELMs, either with or without pellet ELM pacing, the possibility of ELM-induced heat fluxes to unarmored surfaces at the secondary divertor should be examined.…”

Section: Field Line Tracing Of 3d Striationsmentioning

confidence: 99%

Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

Wilcox¹,

Baylor²,

Bortolon³

et al. 2021

Nucl. Fusion

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Edge localized modes (ELMs) are triggered using deuterium pellets injected into plasmas with ITER-relevant low collisionality pedestals, and the resulting peak ELM energy fluence is reduced by approximately 25-50% relative to natural ELMs destabilized at similar pedestal pressures. Cryogenically frozen deuterium pellets are injected from the low-field side of the DIII-D tokamak at frequencies lower than the natural ELM frequency, and heat flux is measured by infrared cameras. Ideal MHD pedestal stability calculations show that without pellet injection, these low collisionality pedestals were limited by their current density (peeling-limited) rather than their pressure gradient (ballooning-limited). ELM triggering success correlates strongly with pellet mass, consistent with the theory that a large pressure perturbation is required to trigger an ELM in low collisionality discharges that are far from the ballooning stability boundary. For sufficiently large pellets, both instantaneous and time-integrated ELM energy deposition measured by infrared cameras is reduced with respect to naturally occurring ELMs at the inner strike point, which is the position where it is largest for natural ELMs. Energy fluence at the outer strike point is less effected. Cameras observing both heat flux and D-alpha emission often find significant toroidally asymmetric striations in the outboard far scrape-off layer resulting from ELMs that are triggered by pellets. Toroidal asymmetries at the inner strike point are similar between natural and pellet-triggered ELMs, suggesting that the reduction in peak heat flux and total fluence at that location is robust for the conditions reported here.

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Quantifying heat and particle flux to primary and secondary divertors for various types of edge-localized-modes

et al. 2022

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Between 15% and 30% of edge-localized-mode (ELM) heat flux can be deposited to regions outside the main divertor including the far scrape-off-layer (SOL), private flux region (PFR), and secondary divertor inner target. Analysis shown here demonstrates that type-I and small ELM plasmas are transported to the PFR and to the secondary inner divertor, which is magnetically isolated from the outer divertor, leading to well-defined heat flux profiles and with peak values that can surpass those at the secondary outer target. Such features are consistently observed for pedestal collisionalities from [Formula: see text] ∼ 1.5 to [Formula: see text] ∼ 3.9. Heat flux profiles of the examined ELM types feature rippled structures due to bursts in the outer far-SOL region but not on the secondary inner target, causing long decay lengths in the time-averaged ELM profiles. The contribution of each ELM type to the total time-averaged power deposited to the secondary divertor has been evaluated, showing that grassy ELMs contribute ∼8%, small ELMs ∼67%, and type-I ELMs ∼85%. These findings imply that small ELMs may yet pose a concern for future machines if some regions of the main wall are not designed to withstand significant heat and particle fluxes. Due to the low intra-ELM heat flux contribution, however, the grassy ELM regime is an attractive option for an ELMing scenario in future machines.

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ELM and inter-ELM heat and particle flux to a secondary divertor in the DIII-D tokamak

Cited by 4 publications

References 51 publications

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

Quantifying heat and particle flux to primary and secondary divertors for various types of edge-localized-modes

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