scholarly journals Tokamak Edge Plasma Turbulence Interaction with Magnetic X-Point in 3D Global Simulations

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 50 ◽  
Author(s):  
Davide Galassi ◽  
Guido Ciraolo ◽  
Patrick Tamain ◽  
Hugo Bufferand ◽  
Philippe Ghendrih ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Edge Plasma ◽  
Turbulent Structures ◽  
Magnetic Shear ◽  
Transport Barrier ◽  
Fluid Turbulence ◽  
Transport Barriers ◽  
Tokamak Edge ◽  
The Impact

Turbulence in the edge plasma of a tokamak is a key actor in the determination of the confinement properties. The divertor configuration seems to be beneficial for confinement, suggesting an effect on turbulence of the particular magnetic geometry introduced by the X-point. Simulations with the 3D fluid turbulence code TOKAM3X are performed here to evaluate the impact of a diverted configuration on turbulence in the edge plasma, in an isothermal framework. The presence of the X-point is found, locally, to affect both the shape of turbulent structures and the amplitude of fluctuations, in qualitative agreement with recent experimental observations. In particular, a quiescent region is found in the divertor scrape-off layer (SOL), close to the separatrix. Globally, a mild transport barrier spontaneously forms in the closed flux surfaces region near the separatrix, differently from simulations in limiter configuration. The effect of turbulence-driven Reynolds stress on the formation of the barrier is found to be weak by dedicated simulations, while turbulence damping around the X-point seems to globally reduce turbulent transport on the whole flux surface. The magnetic shear is thus pointed out as a possible element that contributes to the formation of edge transport barriers.

scholarly journals Formation of the radial electric field profile in the WEST tokamak

2021 ◽  
Author(s):  
Laure Vermare ◽  
Pascale Hennequin ◽  
Cyrille Honore ◽  
Mathieu Peret ◽  
Guilhem Dif-Pradalier ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Electric Field ◽  
Turbulent Transport ◽  
Radial Profile ◽  
Radial Electric Field ◽  
Turbulent Structures ◽  
The West ◽  
Transport Barrier ◽  
Deep Well ◽  
Electric Field Profile

Abstract Sheared flows are known to reduce turbulent transport by decreasing the correlation length and/or intensity of turbulent structures. The transport barrier that takes place at the edge during improved regimes such as H mode, corresponds to the establishment of a large shear of the radial electric field. In this context, the radial shape of the radial electric field or more exactly of the perpendicular $E\times B$ velocity appears as a key element in accessing improved confinement regimes. In this paper, we present the radial profile of the perpendicular velocity measured using Doppler back-scattering system at the edge of the plasma, dominated by the $E\times B$ velocity, during the first campaigns of the WEST tokamak. It is found that the radial velocity profile is clearly more sheared in LSN than in USN configuration for ohmic and low current plasmas ($B=3.7T$ and $q_{95}=4.7$), consistently with the expectation comparing respectively “favourable” versus “unfavourable” configuration. Interestingly, this tendency is sensitive to the plasma current and to the amount of additional heating power leading to plasma conditions in which the $E\times B$ velocity exhibits a deeper well in USN configuration. For example, while the velocity profile exhibits a clear and deep well just inside the separatrix concomitant with the formation of a density pedestal during L-H transitions observed in LSN configuration, deeper $E_r$ wells are observed in USN configuration during similar transitions with less pronounced density pedestal.

Plasma-turbulence suppression and transport-barrier formation by externally driven radiofrequency waves in spherical tokamaks

2001 ◽  
Vol 65 (3) ◽  
pp. 235-253 ◽  
Author(s):  
K. KOMOSHVILI ◽  
S. CUPERMAN ◽  
C. BRUMA
Keyword(s):  
Electric Fields ◽  
Turbulent Transport ◽  
Plasma Turbulence ◽  
Ion Temperature ◽  
Transport Barrier ◽  
Ion Temperature Gradient ◽  
Turbulence Suppression ◽  
Barrier Formation ◽  
Transport Barriers ◽  
Fast Waves

Turbulent transport of heat and particles is the principle obstacle confronting controlled fusion today. We investigate quantitatively the suppression of turbulence and formation of transport barriers in spherical tokamaks by sheared electric fields generated by externally driven radiofrequency (RF) waves, in the frequency range ωA ∼ ω < ωci (where ωA and ωci are the Alfvén and ion cyclotron frequencies).This investigation consists of the solution of the full-wave equation for a spherical tokamak in the presence of externally driven fast waves and the evaluation of the power dissipation by the mode-converted Alfvén waves. This in turn provides a radial flow shear responsible for the suppression of plasma turbulence. Thus a strongly nonlinear equation for the radial sheared electric field is solved, and the turbulent transport suppression rate is evaluated and compared with the ion temperature gradient (ITG) instability increment.

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

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
M. Giacomin ◽  
P. Ricci
Keyword(s):  
Turbulent Transport ◽  
Transport Barrier ◽  
Analytical Estimate ◽  
Analytical Expression ◽  
Density Limit ◽  
Minor Radius ◽  
Transport Regime ◽  
Power Threshold ◽  
Tokamak Edge ◽  
Two Fluid

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.

Turbulent Transport in the Tokamak Edge Plasma and SOL Region

2013 ◽  
Vol 32 (4) ◽  
pp. 496-502 ◽  
Author(s):  
S. Meshkani ◽  
M. Ghoranneviss ◽  
M. Lafouti ◽  
A. Salar Elahi
Keyword(s):  
Turbulent Transport ◽  
Edge Plasma ◽  
Tokamak Edge

FORMATION OF TRANSPORT BARRIER BY SHEARING

2004 ◽  
Vol 18 (12n13) ◽  
pp. 551-571 ◽  
Author(s):  
EUN-JIN KIM
Keyword(s):  
Turbulent Transport ◽  
Transport Barrier ◽  
Zonal Flows ◽  
Barrier Formation ◽  
Laboratory Plasmas ◽  
Transport Barriers

We review the effect of shearing on transport and the formation of transport barriers. The focus is primarily on laboratory plasmas where the formation of transport barriers (the L–H transition) is thought to originate from the turbulence regulation due to both (coherent) mean and (random) zonal flows. We provide quantitative discussion on the reduction of turbulent transport by these flows and elucidate their roles in the barrier formation.

scholarly journals The impact of mixing across the polar vortex edge on Match ozone loss estimates

2007 ◽  
Vol 7 (4) ◽  
pp. 11725-11759 ◽  
Author(s):  
J.-U. Grooß ◽  
R. Müller ◽  
P. Konopka ◽  
H.-M. Steinhorst ◽  
A. Engel ◽  
...  
Keyword(s):  
Time Integration ◽  
Polar Vortex ◽  
Lagrangian Model ◽  
Match Method ◽  
Transport Barrier ◽  
Ozone Loss ◽  
The Impact ◽  
Loss Rates

Abstract. The Match method for quantification of polar chemical ozone loss is investigated mainly with respect to the impact of mixing across the vortex edge onto this estimate. We show for the winter 2002/03 that significant mixing across the vortex edge occurred and was accurately modeled by the Chemical Lagrangian Model of the Stratosphere. Observations of inert tracers and ozone in-situ from HAGAR on the Geophysica aircraft and sondes and also remote from MIPAS on ENVISAT were reproduced well. The model even reproduced a small vortex remnant that was isolated until June 2003 and was observed in-situ by a balloon-borne whole air sampler. We use this CLaMS simulation to quantify the impact of cross vortex edge mixing on the results of the Match method. It is shown that a time integration of the determined vortex average ozone loss rates as performed in Match results in larger ozone loss than the polar vortex average ozone loss in CLaMS. Also, the determination of the Match ozone loss rates can be influenced by mixing. This is especially important below 430 K, where ozone outside the vortex is lower than inside and the vortex boundary is not a strong transport barrier. This effect and further sampling effects cause an offset between vortex average ozone loss rates derived from Match and deduced from CLaMS with an even sampling for the entire vortex. Both, the time-integration of ozone loss and the determination of ozone loss rates for Match are evaluated using the winter 2002/03 CLaMS simulation. These impacts can explain the differences between CLaMS and Match column ozone loss. While the investigated effects somewhat reduce the apparent discrepancy in January ozone loss rates, a discrepancy between simulations and Match remains. However, its contribution to the accumulated ozone loss over the winter is not large.

Comment on determination of electron temperature from Langmuir probe data in tokamak edge plasma

1990 ◽  
Vol 40 (6) ◽  
pp. 678-685 ◽  
Author(s):  
J. Dvořáček ◽  
M. Tichý ◽  
L. Kryška ◽  
J. Stöckel ◽  
F. Žáček ◽  
...  
Keyword(s):  
Electron Temperature ◽  
Langmuir Probe ◽  
Edge Plasma ◽  
Tokamak Edge

Assessment of sensitivity of the efficiency of regional tax spending towards investment attractiveness of the types of economic activity carried out by the residents of advanced development territory

2020 ◽  
pp. 98-110
Author(s):  
Evgeniya Mikhailovna Popova ◽  
Guzel Mukhtarovna Guseinova ◽  
Sergei Borisovich Milov
Keyword(s):  
Economic Activity ◽  
Socioeconomic Development ◽  
Federal District ◽  
Tax Incentives ◽  
Capital Investments ◽  
The Subject ◽  
Investment Process ◽  
The Impact ◽  
Advanced Development

The deficit of subnational budgets and deceleration capital investments in multiple Russian regions increase the relevance of research aimed at improvement of tax incentivizing practice of the regional investment process. The studies focused on determination of the impact of socioeconomic and institutional factors upon the efficiency of investment tax expenses obtained wide circulation within the foreign scientific literature. The subject of this article is the assessment of sensitivity of the efficiency of regional tax expanses towards investment attractiveness of the types of economic activity carried out by the residents of territories of advanced socioeconomic development, created in the subjects of Far Easter Federal District. The scientific novelty and practical values of this research consists in substantiation of the reasonableness of assessment of investment attractiveness of the types of economic activity that are stimulated by tax incentives. Methodology for assessing investment attractiveness is proposed and tested. The conclusion is made that in case of low investment attractiveness of the type of economic activity, which was planned to support by tax incentives, it is required to conduct and additional analysis to avoid unjustified tax expanses.

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