On the nature of blob propagation and generation in the large plasma device: Global GRILLIX studies

Ross, A.; Stegmeir, A.; Mänz, P.; Grošelj, Daniel; Zholobenko, W.; Coster, D.; Jenko, F.

doi:10.1063/1.5095712

Cited by 18 publications

(21 citation statements)

References 55 publications

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“…At the same time a direct comparison to a Boussinesq reduced model revealed that the Boussinesq approximation had only minor quantitative effects. However, this conclusion might possibly not hold true for other parameter regimes [19] and therefore it is safest to abolish it consequently. Besides this, other global features, e.g.…”

Section: Discussionmentioning

confidence: 97%

“…The Boussinesq approximation has often been studied at isolated sub problems, i.e. blob propagation [16,17,18,19]. Here we investigate its impact in a fully turbulent environment and find that it has only minor quantitative impact on results.…”

Section: Introductionmentioning

confidence: 85%

“…3 and follows a sec- ond order convergence, which is a good indication for correct implementation of the equations in GRILLIX. Finally, we want to note that also a validation in slab geometry based on experiments in the Large Plasma Device (LAPD) was performed for which results can be found in [18,19].…”

Section: Verificationmentioning

confidence: 99%

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Global turbulence simulations of the tokamak edge region with GRILLIX

et al. 2019

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Turbulent dynamics in the scrape-off layer (SOL) of magnetic fusion devices is intermittent with large fluctuations in density and pressure. Therefore, a model is required that allows perturbations of similar or even larger magnitude to the time-averaged background value. The fluid-turbulence code GRILLIX is extended to such a global model, which consistently accounts for large variation in plasma parameters. Derived from the drift reduced Braginskii equations, the new GRILLIX model includes electromagnetic and electron-thermal dynamics, retains global parametric dependencies and the Boussinesq approximation is not applied. The penalisation technique is combined with the flux-coordinate independent (FCI) approach [F. Hariri and M. Ottaviani, Comput. Phys. Commun. 184:2419, (2013); A. Stegmeir et al., Comput. Phys. Commun. 198:139, (2016)], which allows to study realistic diverted geometries with X-point(s) and general boundary contours. We characterise results from turbulence simulations and investigate the effect of geometry by comparing simulations in circular geometry with toroidal limiter against realistic diverted geometry at otherwise comparable parameters. Turbulence is found to be intermittent with relative fluctuation levels of up to 40% showing that a global description is indeed important. At the same time via direct comparison, we find that the Boussinesq approximation has only a small quantitative impact in a turbulent environment. In comparison to circular geometry the fluctuations are reduced in diverted geometry, which is related to a different zonal flow structure. Moreover, the fluctuation level has a more complex spatial distribution in diverted geometry. Due to local magnetic shear, which differs fundamentally in circular and diverted geometry, turbulent structures become strongly distorted in the perpendicular direction and are eventually damped away towards the X-point.

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Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 85%

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Global turbulence simulations of the tokamak edge region with GRILLIX

et al. 2019

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“…(2019) and Ross et al. (2019) showing that there is no substantial difference in the equilibrium profiles when the Boussinesq approximation is considered. Although in theoretical (Chôné et al.…”

Section: Simulation Modelmentioning

confidence: 93%

“…The effect of the Boussinesq approximation is discussed in Yu et al (2006) and Bodi et al (2011), showing that it has a negligible effect on SOL turbulence. In the edge, the validity of the Boussinesq approximation is addressed in Stegmeir et al (2019) and Ross et al (2019) showing that there is no substantial difference in the equilibrium profiles when the Boussinesq approximation is considered. Although in theoretical (Chôné et al 2014(Chôné et al , 2015 and experimental (Viezzer et al 2013) works it is shown that neoclassical corrections can play an important role in the onset of transport barriers and, consequently, in the L-H transition, we do not include these effects in our model.…”

Section: Simulation Modelmentioning

confidence: 99%

Investigation of turbulent transport regimes in the tokamak edge by using two-fluid simulations

Giacomin

Ricci

2020

J. Plasma Phys.

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The results of flux-driven, two-fluid simulations in single-null configurations are used to investigate the processes determining the turbulent transport in the tokamak edge. Three turbulent transport regimes are identified: (i) a developed transport regime with turbulence driven by an interchange instability, which shares a number of features with the standard L-mode of tokamak operation; (ii) a suppressed transport regime, characterized by a higher value of the energy confinement time, low-amplitude relative fluctuations driven by a Kelvin–Helmholtz instability, a strong $\boldsymbol {E}\times \boldsymbol {B}$ sheared flow and the formation of a transport barrier, which recalls the H-mode; and (iii) a degraded confinement regime, characterized by a catastrophically large interchange-driven turbulent transport, which recalls the crossing of the Greenwald density limit. We derive an analytical expression of the pressure gradient length in the three regimes. The transition from the developed transport regime to the suppressed transport regime is obtained by increasing the heat source or decreasing the collisionality and vice versa for the transition from the developed transport regime to the degraded confinement regime. An analytical expression of the power threshold to access the suppressed transport regime, linked to the power threshold for H-mode access, as well as the maximum density achievable before entering the degraded confinement regime, related to the Greenwald density, are also derived. The experimental dependencies of the power threshold for H-mode access on density, tokamak major radius and isotope mass are retrieved. The analytical estimate of the density limit contains the correct dependence on the plasma current and on the tokamak minor radius.

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Introducing electromagnetic effects in Soledge3X

Düll,

Bufferand,

Serre

et al. 2024

Contrib. Plasma Phys

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In the pedestal region, electromagnetic effects affect the evolution of micro‐instabilities and plasma turbulence. The transport code Soledge3X developed by the CEA offers an efficient framework for turbulent 3D simulation on an electrostatic model with a fixed magnetic field. The physical accuracy of the model is improved with electromagnetic induction, driven by the local value of the parallel component of the electromagnetic vector potential , known from Ampère's law. It is solved implicitly in a coupled system with the vorticity equation on the electric potential . The consequence is a basic electromagnetic behavior in the form of shear Alfvén waves. A finite electron mass prevents unphysical speeds but requires solving for the time evolution of the parallel current density in the generalized Ohm's law. This term can be analytically included with little computational overhead in the system on and and improves its numerical condition, facilitating the iterative solving procedure. Simulations on a periodic slab case let us observe the predicted bifurcation of the wave propagation speed between the Alfvén wave and the electron thermal wave speeds for varying perpendicular wavenumbers. The first results on a circular geometry with a limiter attest to the feasibility of turbulent electromagnetic scenarios.

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On the nature of blob propagation and generation in the large plasma device: Global GRILLIX studies

Cited by 18 publications

References 55 publications

Global turbulence simulations of the tokamak edge region with GRILLIX

Global turbulence simulations of the tokamak edge region with GRILLIX

Investigation of turbulent transport regimes in the tokamak edge by using two-fluid simulations

Introducing electromagnetic effects in Soledge3X

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