The effect of safety factor and magnetic shear on turbulent transport in nonlinear gyrokinetic simulations

2006 ◽  
Vol 13 (2) ◽  
pp. 022305 ◽  
Author(s):  
J. E. Kinsey ◽  
R. E. Waltz ◽  
J. Candy
Keyword(s):  
Safety Factor ◽  
Turbulent Transport ◽  
Magnetic Shear ◽  
Gyrokinetic Simulations

scholarly journals Flux-driven gyrokinetic simulations of ion turbulent transport at low magnetic shear

2010 ◽  
Vol 260 ◽  
pp. 012017 ◽  
Author(s):  
Y Sarazin ◽  
A Strugarek ◽  
G Dif-Pradalier ◽  
J Abiteboul ◽  
S Allfrey ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Magnetic Shear ◽  
Gyrokinetic Simulations

scholarly journals Eliminating turbulent self-interaction through the parallel boundary condition in local gyrokinetic simulations

2020 ◽  
Vol 86 (2) ◽  
Author(s):  
Justin Ball ◽  
Stephan Brunner ◽  
Ajay C.J.
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Correlation Length ◽  
Statistical Properties ◽  
Base Case ◽  
Magnetic Shear ◽  
Turbulent Eddies ◽  
Simulation Domain ◽  
Gyrokinetic Simulations ◽  
Full Domain

In this work, we highlight an issue that may reduce the accuracy of many local nonlinear gyrokinetic simulations – turbulent self-interaction through the parallel boundary condition. Given a sufficiently long parallel correlation length, individual turbulent eddies can span the full domain and ‘bite their own tails’, thereby altering their statistical properties. Such self-interaction is only modelled accurately when the simulation domain corresponds to a full flux surface, otherwise it is artificially strong. For Cyclone Base Case parameters and typical domain sizes, we find that this mechanism modifies the heat flux by approximately 40 % and it can be even more important. The effect is largest when using kinetic electrons, low magnetic shear and strong turbulence drive (i.e. steep background gradients). It is found that parallel self-interaction can be eliminated by increasing the parallel length and/or the binormal width of the simulation domain until convergence is achieved.

scholarly journals Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

2013 ◽  
Vol 20 (12) ◽  
pp. 122312 ◽  
Author(s):  
D. Told ◽  
F. Jenko ◽  
T. Görler ◽  
F. J. Casson ◽  
E. Fable ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Gyrokinetic Simulations

Gyrokinetic Simulations of Turbulent Transport in a Ring Dipole Plasma

2009 ◽  
Vol 103 (5) ◽  
Author(s):  
Sumire Kobayashi ◽  
Barrett N. Rogers ◽  
William Dorland
Keyword(s):  
Turbulent Transport ◽  
Gyrokinetic Simulations

scholarly journals Pedestal temperature models based on first and second stability limits of ballooning modes

2006 ◽  
Vol 24 (1) ◽  
pp. 113-116 ◽  
Author(s):  
THAWATCHAI ONJUN
Keyword(s):  
Pressure Gradient ◽  
Safety Factor ◽  
Type I ◽  
Magnetic Shear ◽  
Ballooning Mode ◽  
Bootstrap Current ◽  
Stability Limits

Models for the prediction of electron pedestal temperatures at the edge of type I ELMy H-mode plasmas are developed. These models are based on theory motivated concepts for pedestal width and pressure gradient. The pedestal pressure gradient is assumed to be limited by high n ballooning mode instabilities, where both the first and second stability limits are considered. The effect of the bootstrap current, which reduces the magnetic shear in the steep pressure gradient region at the edge of the H-mode plasma, can result in access to the second stability of ballooning mode. In these pedestal models, the magnetic shear and safety factor are calculated at one pedestal width away from separatrix. The predictions of these models are compared with the experimental electron pedestal temperatures for type I ELMy H-mode discharges obtained from the latest public version (version 3.2) in the International Tokamak Physics Activity Edge (ITPA) Pedestal Database.

scholarly journals How eigenmode self-interaction affects zonal flows and convergence of tokamak core turbulence with toroidal system size

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
Ajay C. J. ◽  
Stephan Brunner ◽  
Ben McMillan ◽  
Justin Ball ◽  
Julien Dominski ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Zonal Flow ◽  
System Size ◽  
Flow Shear ◽  
Direction Parallel ◽  
Zonal Flows ◽  
Radial Extent ◽  
Modulational Instabilities ◽  
Gyrokinetic Simulations ◽  
The Magnetic Field

Self-interaction is the process by which a microinstability eigenmode that is extended along the direction parallel to the magnetic field interacts non-linearly with itself. This effect is particularly significant in gyrokinetic simulations accounting for kinetic passing electron dynamics and is known to generate stationary $E\times B$ zonal flow shear layers at radial locations near low-order mode rational surfaces (Weikl et al. Phys. Plasmas, vol. 25, 2018, 072305). We find that self-interaction, in fact, plays a very significant role in also generating fluctuating zonal flows, which is critical to regulating turbulent transport throughout the radial extent. Unlike the usual picture of zonal flow drive in which microinstability eigenmodes coherently amplify the flow via modulational instabilities, the self-interaction drive of zonal flows from these eigenmodes are uncorrelated with each other. It is shown that the associated shearing rate of the fluctuating zonal flows therefore reduces as more toroidal modes are resolved in the simulation. In simulations accounting for the full toroidal domain, such an increase in the density of toroidal modes corresponds to an increase in the toroidal system size, leading to a finite system size effect that is distinct from the well-known profile shearing effect.

Gyrokinetic simulations of turbulent transport: size scaling and chaotic behaviour

2010 ◽  
Vol 52 (12) ◽  
pp. 124038 ◽  
Author(s):  
L Villard ◽  
A Bottino ◽  
S Brunner ◽  
A Casati ◽  
J Chowdhury ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Chaotic Behaviour ◽  
Size Scaling ◽  
Gyrokinetic Simulations

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.

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