Optimization of turbulence reduced model free parameters based on L‐mode experiments and 2D transport simulations

Baschetti, Serafina; Bufferand, Hugo; Ciraolo, Guido; Fedorczak, N.; Ghendrih, Philippe; Serre, Éric; Tamain, P.

doi:10.1002/ctpp.201700163

Cited by 11 publications

(18 citation statements)

References 8 publications

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“…sink k ∼ nk 2 ⊥ only. Note however that recent studies do include a dependence on machine parameters in this sink term in the Bufferand et al's model [21][22][23] . A regression analysis has been conducted to determine the corresponding constant C sink,Bu f f such that equation…”

Section: Complete 1d Transport Model and Implementation In Divoptmentioning

confidence: 99%

“…Bufferand's equation for the turbulent kinetic energy is based on a predator-prey model for the turbulence intensity derived by Miki et al 20 with some ad hoc adaptations to obtain a transport model for the turbulent kinetic energy. This model has later been refined by using global confinement scaling laws in its closure of the dissipation [21][22][23] .…”

Section: Introductionmentioning

confidence: 99%

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Turbulent kinetic energy in 2D isothermal interchange-dominated scrape-off layer E × B drift turbulence: Governing equation and relation to particle transport

2021

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This paper studies the turbulent kinetic energy (k ⊥ ) in 2D isothermal electrostatic interchange-dominated ExB drift turbulence in the scrape-off layer, and its relation to particle transport. An evolution equation for the former is analytically derived from the underlying turbulence equations. Evaluating this equation shows that the dominant source for the turbulent kinetic energy is due to interchange drive, while the parallel current loss to the sheath constitutes the main sink. Perpendicular transport of the turbulent kinetic energy seems to play a minor role in the balance equation. Reynolds stress energy transfer also seems to be negligible, presumably because no significant shear flow develops under the given assumptions of isothermal sheath-limited conditions in the open field line region. The interchange source of the turbulence is analytically related to the average turbulent ExB energy flux, while a regression analysis of TOKAM2D data suggests a model that is linear in the turbulent kinetic energy for the sheath loss. A similar regression analysis yields a diffusive model for the average radial particle flux, in which the anomalous diffusion coefficient scales with the square root of the turbulent kinetic energy. Combining these three components, a closed set of equations for the mean-field particle transport is obtained, in which the source of the turbulence depends on mean flow gradients and k ⊥ through the particle flux, while the turbulence is saturated by parallel losses to the sheath. Implementation of this new model in a 1D mean-field code shows good agreement with the original TOKAM2D data over a range of model parameters.Recently, Bufferand et al. 19 proposed a mean-field model for the turbulent particle transport in the plasma edge that draws inspiration from these RANS models. More specifically, the model bears similarity to k(−ε) models, where equations for the turbulent kinetic energy k (and dissipation ε) are solved to provide time-and length scales to model the closure terms 18 . Bufferand et al. proposed a diffusive model for the radial particle transport where the anomalous trans-

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Section: Complete 1d Transport Model and Implementation In Divoptmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Turbulent kinetic energy in 2D isothermal interchange-dominated scrape-off layer E × B drift turbulence: Governing equation and relation to particle transport

2021

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“…The minimum error is found to be for 0 = 1.33 × 10 3 (m 2 /s 2 ) and = 1.3 × 10 −3 (m 2 s −1 eV −2 ). The minimum absolute error is found to be Err min = 2 × 10 −2 (m 2 /s), Although usually considered as the standard scaling for diffusion coefficients, and in particular an upper limit, D Bohm is actually too small to account for blob convective transport particularly effective in the SOL region, [8] as one can see in the plot. Right: 2D map of diffusivity self-consistently calculated with the − model.…”

Section: Reduction and Optimization Of The Degrees Of Freedom Of The mentioning

confidence: 96%

Optimization of turbulence reduced model free parameters based on L‐mode experiments and 2D transport simulations

Baschetti

Bufferand

Ciraolo

et al. 2018

Contributions to Plasma Physics

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In this paper, a κ−ϵ transport model is presented as a turbulence reduction tool for a typical ohmic L‐mode discharge plasma in a divertor‐configurated tokamak. Taking a Tokamak à configuration variable (TCV) study case, a feedback loop procedure is performed using the SolEdge2D code to acquire plasma diffusivity at the outer mid‐plane. The κ−ϵ model is calibrated through its free parameters with the aim of recovering the diffusivity calculated in the feedback procedure. Finally, it is shown that the model can self‐consistently calculate diffusivity in the whole domain, recovering the poloidal asymmetries due to interchange instabilities.

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“…[85], Figure 14. On panel (a), we have reproduced the particle flux as obtained with the procedure of midplane profile tuning of the transport coefficients [24], and assuming that these coefficients can be extrapolated to the whole Figure 14: Sketch of the 2D transport pattern in TCV in the large X-point height configuration. Pattern of the particle flux in the poloidal plane, simulations with SolEdge2D-EIRENE but without κ-ε self-consistent turbulent transport, sketch from Ref.…”

Section: Transport Properties In the Poloidal Planementioning

confidence: 99%

“…Furthermore, such symmetric transport pattern is known to disagree with experimental evidence that suggests ballooned transport [25,26,27]. Another simulation was performed with a different choice of transport coefficients, tuning the radial profile to fit the midplane profiles [24] and then extrapolating these to the poloidal plane by enforcing strongly ballooned transport, Figure 14, panel (b). A modest improvement when Figure 15: Sketch of the 2D transport pattern in TCV in the large Xpoint height configuration.…”

Section: Transport Properties In the Poloidal Planementioning

confidence: 99%

Self-consistent cross-field transport model for core and edge plasma transport

Baschetti

Bufferand²,

Ciraolo³

et al. 2021

Nucl. Fusion

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The 2D mean-field plasma edge transport description of plasma wall interaction is completed by a κ-ε model as in Reynolds Average Navier Stokes simulations for neutral fluids. The local evolution of the turbulent kinetic energy κ and its dissipation rate ε are revisited and slightly modified. It is shown that the κ-ε extends the quasilinear approach by self-consistently determining κ and the relevant time κ/ε leading to the diffusion coefficient κ 2 /ε. The κ-ε evolution is also shown to be equivalent to both coupled Ginzburg-Landau amplitude equations and predator-prey systems where κ is the prey and ε the predator. The dissipation process ε we enforce describes the small scale dissipation of Kolmogorov cascades. It depends on a free parameter akin to a velocity V . The chosen closure relates V to the the parallel connection time and the normalized Scrape-Off layer width qρ * , q is the safety factor and ρ * the ratio of the characteristic Larmor radius and plasma minor radius. A 1D model with κ-ε self-organized transport is used for comparison to empirical scaling laws of SOL width and energy confinement time in L-mode plasmas. Shortfalls of the scaling laws are analyzed. Possible changes of the closure for V are discussed. The 1D model is also used to test the transport response to a dependence of V to large scale velocity shear. Spontaneous confinement improvement when increasing the heating power 1 is observed with the development of an interface barrier at the separatrix. Plasma-wall interaction simulations for TCV and WEST are analyzed. A single scalar free parameter tunes the cross field transport. Experimental midplane and divertor profiles are compared to the simulations. Remarkable agreement is observed. The SOL width determined by the simulation for WEST is close to the experimental value with less than 20 % difference, while the scaling law for L-mode is off my more than a factor 3. The turbulent transport described by the κ-ε is not homogeneous, but ballooned as experimentally observed together with cross-field transport in the divertor SOL on the low field side, and nearly none in the private flux region.

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Optimization of turbulence reduced model free parameters based on L‐mode experiments and 2D transport simulations

Cited by 11 publications

References 8 publications

Turbulent kinetic energy in 2D isothermal interchange-dominated scrape-off layer E × B drift turbulence: Governing equation and relation to particle transport

Turbulent kinetic energy in 2D isothermal interchange-dominated scrape-off layer E × B drift turbulence: Governing equation and relation to particle transport

Optimization of turbulence reduced model free parameters based on L‐mode experiments and 2D transport simulations

Self-consistent cross-field transport model for core and edge plasma transport

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