Shaping effects on scrape-off layer plasma turbulence: A rigorous validation of three-dimensional simulations against TCV measurements

Riva, Fabio; Tsui, C.; Boedo, J. A.; Ricci, Paolo; Team, Tcv

doi:10.1063/1.5123451

Cited by 16 publications

(20 citation statements)

References 62 publications

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“…In particular, our theoretical scaling law does not include the effect of plasma triangularity, which has been studied with GBS in Refs. [73,74] for a limited configuration, showing that the near SOL width is enhanced (reduced) by positive (negative) values of triangularity, in agreement with experimental observations [75]. In addition, interchange-like turbulence, which can develop along the divertor leg, can increase the power fall-off length at the target plate [76].…”

Section: Near Solsupporting

confidence: 81%

Theory-based scaling laws of near and far scrape-off layer widths in single-null L-mode discharges

Giacomin,

Stagni,

Ricci

et al. 2021

Preprint

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Theory-based scaling laws of the near and far scrape-off layer (SOL) widths are analytically derived for L-mode diverted tokamak discharges by using a two-fluid model. The near SOL pressure and density decay lengths are obtained by leveraging a balance among the power source, perpendicular turbulent transport across the separatrix, and parallel losses at the vessel wall, while the far SOL pressure and density decay lengths are derived by using a model of intermittent transport mediated by filaments. The analytical estimates of the pressure decay length in the near SOL is then compared to the results of three-dimensional, flux-driven, global, two-fluid turbulence simulations of L-mode diverted tokamak plasmas, and validated against experimental measurements taken from an experimental multi-machine database of divertor heat flux profiles, showing in both cases a very good agreement. Analogously, the theoretical scaling law for the pressure decay length in the far SOL is compared to simulation results and to experimental measurements in TCV L-mode discharges, pointing out the need of a large multi-machine database for the far SOL decay lengths.

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Section: Near Solsupporting

confidence: 81%

Theory-based scaling laws of near and far scrape-off layer widths in single-null L-mode discharges

Giacomin,

Stagni,

Ricci

et al. 2021

Preprint

Self Cite

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“…However, the quality of the validation is very high, with values of Q = 18.6 − 19.4, reflecting the large number of observables used in the validation. The results of the quantitative analysis correspond to a lower level of agreement and a significantly higher quality compared to previous works using the same methodology, such as Ricci et al, 2015 [24], which found a χ = 0.5 − 0.75 with a Q ≈ 4 for TORPEX plasmas and Riva et al, 2020 [16] which found a value of χ = 0.45 and Q ≈ 4 for limited TCV discharges. We note that a companion work to this paper, published as Galassi et al, 2021 [25] found χ = 0.85−1.0 and Q ≈ 4 in TORPEX plasmas with an internal X-point.…”

Section: Quantitative Validation and Sensitivity Analysissupporting

confidence: 45%

“…Direct numerical turbulence simulations require more sophisticated physical models than transport codes, and orders-of-magnitude more computational resources due to the 3D multi-scale nature of turbulence. Nevertheless, advances in numerical methods and larger, faster supercomputers mean that full-size † turbulence simulations of the boundary region of existing experimental devices like COMPASS [12]- [14], MAST [15], TCV [16], Alcator C-mod [17]- [19], AUG [20] and DIII-D [17] are now achievable, allowing direct comparison between turbulence simulations and experimental results.…”

Section: Introductionmentioning

confidence: 99%

“…Importantly, validation here is not a binary result, but rather a tool for checking the fidelity of the simulations and guiding targeted development of the models -with repeated validation suggested as part of a model testing and development cycle [22]. This methodology has already been used to test boundary turbulence simulations in basic plasma physics devices [23]- [25] and limited tokamak plasmas [16].…”

Section: Introductionmentioning

confidence: 99%

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Validation of edge turbulence codes against the TCV-X21 diverted L-mode reference case

Oliveira,

Body,

Galassi

et al. 2021

Preprint

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Full-size turbulence simulations of the divertor and scrape-off-layer of existing tokamaks have recently become feasible, allowing direct comparisons of turbulence simulations to experimental measurements. We present a validation of three flux-driven turbulence codes -GBS, GRILLIX and TOKAM3X -against an experimental dataset from diverted Ohmic L-mode discharges on the TCV tokamak. This "TCV-X21" dataset covers the divertor targets, volume, entrance and the outboard midplane via 5 diagnostic systems, giving a total of 45 comparison observables over two toroidal field directions. The simulations show good agreement at the outboard midplane for most observables. At the divertor targets and in the divertor volume, several individual observables show good agreement, but the overall match is lower than at the outboard midplane. The simulations typically find the correct order-of-magnitude and the approximate shape for the divertor mean profiles, with the match varying for different observables and codes. The experimental profiles of the divertor density, potential, current and velocity vary strongly with field direction, while a weaker effect is found in the simulations. The simulated divertor profiles are found to be sensitive to the choice of sheath boundary conditions and the use of artificially increased collisionality. Additionally, the observed divertor flows suggest that divertor neutral ionisation is nonnegligible. This indicates that the match could be improved by using improved boundary conditions, more realistic parameters and including self-consistent neutral physics. Future validation and benchmarking against the TCV-X21 reference dataset will assess the impact of improvements to the codes and will guide their targeted development -a process which can be extended to other turbulence codes via the freely available TCV-X21 reference dataset. As such, this work assesses the current capabilities of edge/divertor turbulence simulations and provides a systematic path towards their improved interpretive and predictive capability.

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“…Ultimately, however, in order to develop full predictive capabilities, these codes need to undergo a thorough validation with experimental data. Initially, validation exercises focused on simple magnetic configurations [22,23], while more recently they have been extended to larger experiments, as TCV (Tokamak à Configuration Variable [24]), in limiter configuration [25]. Multi-code validations of seeded blobs had been performed against TORPEX [26] and MAST [27] experiments.…”

Section: Introductionmentioning

confidence: 99%

Validation of edge turbulence codes in a magnetic X-point scenario in TORPEX

et al. 2022

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Transport processes around the magnetic X-point of tokamaks, such as turbulence and mean-field drifts, are scarcely understood. The assessment of the capability of turbulence codes to quantitatively reproduce these dynamics has been hampered by limitations in computational power and available experimental data. In this paper, we present a rigorous validation of full-scale simulations of a newly developed X-point scenario in the basic toroidal plasma device TORPEX, performed with the four state-of-the-art codes FELTOR, GBS, GRILLIX and STORM. Highresolution Langmuir probe array measurements of various time-averaged and fluctuating quantities and across the entire cross-section of TORPEX show that this X-point scenario features the key ingredients of X-point dynamics, such as small-scale fluctuations as well as background drifts.The codes are able to qualitatively reproduce some characteristics of the time-averaged fields, such as the ion saturation current profiles at mid-height, the plasma up-down asymmetry and the blob trajectories. A quantitative agreement is found for the background E × B velocity pattern, while the fluctuation levels are generally underestimated by typically factors of 2 or more, thus background fluxes are found to dominate over turbulent ones in simulations. The sensitivity of the simulation results on the plasma collisionality and on the position of the sources are tested in GBS, showing a mild effect on the overall quantitative agreement with the experiment. Overall, this validation reveals the challenges to reproduce the plasma dynamics near an X-point, and provides a clear path to a quantitative, and computationally relatively inexpensive assessment of future developments in turbulence codes.

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Shaping effects on scrape-off layer plasma turbulence: A rigorous validation of three-dimensional simulations against TCV measurements

Cited by 16 publications

References 62 publications

Theory-based scaling laws of near and far scrape-off layer widths in single-null L-mode discharges

Theory-based scaling laws of near and far scrape-off layer widths in single-null L-mode discharges

Validation of edge turbulence codes against the TCV-X21 diverted L-mode reference case

Validation of edge turbulence codes in a magnetic X-point scenario in TORPEX

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