Predictive modelling of L and H confinement modes and edge pedestal characteristics

Kalupin, D.; Tokar, M. Z.; Unterberg, B.; Loozen, X.; Pilipenko, Denis

doi:10.1088/0029-5515/45/6/008

Cited by 26 publications

(37 citation statements)

References 35 publications

(60 reference statements)

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“…The dominant linear instabilities in this parameter regime are resistive [34] even when the steeper temperature gradients give them an ITG character. Turbulence at the same parameters is often assumed without diagnosis to follow not only the linear mechanism but also the linear scales, whether in interpreting a computation [32,33] or in forming transport models based upon edge turbulence [35,36]. By contrast, it is known via control tests and in-context diagnosis that edge turbulence is viable in the absence of linear instabilities [6,7], and can eliminate the linear destabilisation mechanism [5,25].…”

Section: Discussionmentioning

confidence: 99%

Edge Turbulence and its Interaction with the Equilibrium

Scott

2006

Contrib. Plasma Phys.

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Tokamak edge turbulence is studied using three dimensional computations in a transcollisional, electromagnetic gyrofluid model. All scales between the ion gyroradius and the profile scale length are carried for up to the transport time scale. Profiles and the MHD equilibrium are time dependently self consistent. Basic properties of the turbulence are shown. Zonal flows are compressible and not in equilibrium, though the electric field profile on larger scales is indeed in equilibrium. Edge turbulence in the closed field line region maintains its character whether a scrape-off layer is present, though in the SOL region it becomes interchange like. Divertor separatrix topology is briefly considered, with little effect on the general turbulence/equilibrium situation. Basic situation of the tokamak edgeThe physical situation of the tokamak edge is defined by its parameters. The profile scale length L ⊥ is very short compared to the minor and major radii a and R and therefore the scale ratios L ⊥ /qR and 2L ⊥ /R which determine the general roles of the parallel dynamics and the toroidal interchange forcing are very small. Drift wave turbulence occupies mostly the perpendicular wavenumber range 0.1 > k ⊥ ρ s > 1 and involves frequencies in the range of the diamagnetic frequency at each scale, or about 0.1 to 1 times c s /L ⊥ [1,2]. Here, c s is the acoustic sound speed and ρ s is the ion sound gyroradius. The parallel wavenumber range is limited by the flux surface geometry to k qR ∼ 1 as larger values involve stronger dissipation/damping [2] and smaller values are disallowed by the geometry, specifically field line connection [3]. Due to the small size of L ⊥ /qR the electron thermal transit is not arbitrarily fast; indeed the statementμ ≡ (m e /M i )(qR/L ⊥ ) 2 > 1 essentially defines the edge region in which strongly nonadiabatic electron dynamics is expected [4,5]. The drift wave collisionality given by C = (0.51ν e L ⊥ /c s )μ is also larger than unity, so that the physics of collisional drift wave turbulence [2] and its associated self sustained turbulence nonlinear instability [6,7] enters. In modern tokamaks the edge pressure is large enough to make the drift Alfvén parameterβ = (4πp e /B2 )(qR/L ⊥ ) 2 also larger than unity, so that the drift wave physics becomes electromagnetic [8]. These features together all lead one to expect a robust physical situation in which none of the familiar restrictive limits (linearity, electrostatic adiabatic electrons, or even MHD) are applicable.This also applies to scale separation. While it is still reasonable to study edge turbulence within a local model in order to diagnose its basic character, the drift parameter δ = ρ s /L ⊥ is typically larger than 10 −2 , so that the longer wavelength component of the drift wave spectrum runs up against the limits placed by the scale length. Here, electromagnetic drift wave turbulence runs into the MHD equilibrium itself, as defined by the balances describing the Pfirsch-Schlüter currents. Indeed, as the turbulence drives zonal ExB fl...

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Section: Discussionmentioning

confidence: 99%

Edge Turbulence and its Interaction with the Equilibrium

Scott

2006

Contrib. Plasma Phys.

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“…The main line of thinking is the mitigation of drift instabilities and non-linear structures, arising on a non-linear stage of instabilities, through the shear of drift motion induced by the radial electric field (Diamond 1994, Terry 2000. Other approaches speculate on the role of the density gradient at the edge in the suppression of ITG-TE modes (Kalupin et al, 2005) and reduction of DA instabilities with decreasing plasma collisionality (Kerner, 1998;Rogers et al, 1998;Guzdar, 2001), the sharpness of the safety factor profile in the vicinity of the magnetic separatrix in a divertor configuration, etc. To prove the importance of a particular physical mechanism, the ability to solve numerically heat transport equations, allowing the formation of ETB, and to calculate the time evolution of the plasma parameter profiles is of principle importance.…”

Section: Numerical Solutionmentioning

confidence: 99%

Modelling of Profile Evolution by Transport Transitions in Fusion Plasmas

Tokar¹

2011

Two Phase Flow, Phase Change and Numerical Modeling

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“…The structure of the code and the transport model are described in detail in Refs. [6,7]. The code solves one-dimensional transport equations for the densities and temperatures of electrons, main and impurity ions and the current diffusion equation.…”

Section: Modeling Of the Etb Formation With The Ritm-codementioning

confidence: 99%

“…Transport coefficients, i.e., the particle diffusivitiesD e,Z ⊥ , pinch velocities V e,Z ⊥ and heat diffusivities χ e,i ⊥ of electrons and different ions of the charged Z are computed according to the transport model introduced in Ref. [7]. This model embraces drift instabilities of different nature, which are divided into "central" and "edge" modes.…”

Section: Modeling Of the Etb Formation With The Ritm-codementioning

confidence: 99%

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RITM-Code Modelling of Plasmas with Edge Transport Barrier

Kalupin¹,

Tokar²,

Unterberg³

et al. 2006

Contrib. Plasma Phys.

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Conditions for the formation of the edge transport barrier (ETB) in tokamaks are investigated by means of onedimensional transport modeling performed for the characteristic parameter range of the TEXTOR tokamak. The computations predict the formation of the ETB at the heating power given by the multi-machine scaling if the fraction of convective heat losses from the plasma does not exceed 50%. An increase of the amount of heat lost through convection above this critical value shifts the formation of ETB to a power several times above the level given by the scaling. For given plasma parameters, the ratio of the conductive to convective heat losses at the plasma edge is determined by the penetration of neutrals. By switching from a divertor to a limiter configuration when the distance between the LCMS and neutralizing plates decreases, this ratio increases due to the higher fraction of particles ionized inside the last closed magnetic surface (LCMS). This can be the reason for the higher H-mode power threshold in limiter tokamaks. First experimental results obtained in TEXTOR demonstrate a good agreement of the power required for ETB formation with the value calculated with 1.5D transport code RITM prior to the experiment.

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Predictive modelling of L and H confinement modes and edge pedestal characteristics

Cited by 26 publications

References 35 publications

Edge Turbulence and its Interaction with the Equilibrium

Edge Turbulence and its Interaction with the Equilibrium

Modelling of Profile Evolution by Transport Transitions in Fusion Plasmas

RITM-Code Modelling of Plasmas with Edge Transport Barrier

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