Coherent drift-wave structures in toroidal plasmas

1996 ◽  
Vol 56 (3) ◽  
pp. 605-613 ◽  
Author(s):  
W. Horton ◽  
T. Tajima ◽  
J.-Y. Kim ◽  
Y. Kishimoto ◽  
M. Ottaviani
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Marginal Stability ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Toroidal Plasmas ◽  
Convective Structures ◽  
Drift Wave ◽  
Particle Simulations ◽  
Two Phases

Using the ion-temperature-gradient-driven drift waves as a paradigm for drift-wave anomalous transport, we explore the structure of the linear and nonlinear modes. Two phases of transport are shown to exist: (i) Bohm-like transport for parameters close to marginal stability; (ii) gyro-Bohm transport for turbulent convection cells in systems driven away from marginal stability. Nonlinear relaxation to large-scale coherent convective structures is observed in three-dimensional toroidal particle simulations.

Envelope nonlinear drift structures in a non-equilibrium plasma near the boundary of marginal stability

1998 ◽  
Vol 59 (1) ◽  
pp. 179-191 ◽  
Author(s):  
TATIANA A. DAVYDOVA ◽  
ALEXEI YU. PANKIN
Keyword(s):  
Numerical Simulation ◽  
Temperature Gradient ◽  
Wave Interaction ◽  
Marginal Stability ◽  
Driving Mechanism ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Equilibrium Plasma ◽  
Explosive Instability ◽  
Special Cases

An explosive instability of the ion-temperature-gradient (ITG)-driven modes (ηi modes) near the boundary of marginal stability is considered as a driving mechanism for subcritical turbulence. It is shown that boundedness of the wave interaction region leads to saturation of the instability. The possibility of coherent soliton-like structure formation in both slab and toroidal geometries is demonstrated by numerical simulation. An analytical soliton solution is found in some special cases.

Anomalous tungsten transport driven by ion temperature gradient turbulence

2021 ◽  
Author(s):  
Shaokang Xu ◽  
Shinya Maeyama ◽  
Tomohiko Watanabe
Keyword(s):  
Particle Transport ◽  
Large Scale ◽  
Critical Density ◽  
Small Scale ◽  
Particle Diffusion ◽  
Tungsten Particle ◽  
Ion Temperature ◽  
Nonlinear Excitation ◽  
Ion Temperature Gradient ◽  
Gyrokinetic Simulations

Abstract The present study reveals that the anomalous tungsten particle transport based on the nonlinear gyrokinetic simulations shares some similarities with that of the linear gyrokinetic study, meanwhile there exist some significant differences. In particular, nonlinear excitation of the linearly stable modes plays a non-negligible role in anomalous tungsten particle transport. The highlighted results are the downshift of the critical density gradient for zero tungsten particle transport and the mod- ification of the poloidal profile of the outward tungsten particle transport, which are both related to the small scale turbulent fluctuations. The former one is due to the outward particle convection produced by the linearly stable modes. The later one is brought by both the linearly stable modes and the large-scale eddies with finite ballooning angle, which flatten the poloidal profile of the particle diffusion and further shift the peak positions of the strongest outward particle transport to the high poloidal angle regions.

scholarly journals Investigation of tokamak turbulent avalanches using wave-kinetic formulation in toroidal geometry

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Camille Gillot ◽  
Guilhem Dif-Pradalier ◽  
Xavier Garbet ◽  
Olivier Panico ◽  
Yanick Sarazin ◽  
...  
Keyword(s):  
Coupled System ◽  
Wave Turbulence ◽  
Ion Temperature ◽  
Flow Shear ◽  
Ion Temperature Gradient ◽  
Kinetic Formulation ◽  
Drift Wave Turbulence ◽  
Drift Wave ◽  
Low Field ◽  
Primary Driver

The interplay between toroidal drift-wave turbulence and tokamak profiles is investigated using a wave-kinetic description. The coupled system is used to investigate the interplay between marginally stable toroidal drift-wave turbulence and geodesic acoustic modes (GAMs). The coupled system is found to be unstable. Notably, the most unstable mode corresponds to the resonance between the turbulent wave radial group velocity and the GAM phase velocity. For a low-field-side ballooned drift-wave growth, a background flow shear breaks the symmetry between inwards- and outwards-travelling instabilities. Although this turbulence–GAM coupling may not be the primary driver for avalanches in standard core ion temperature gradient simulations, this mechanism is generic and displays many of the expected features, and should be of interest in several other regimes, which include towards the edge or in the presence of energetic particles.

scholarly journals Advancing the physics basis for quasi-helically symmetric stellarators

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
A. Bader ◽  
B. J. Faber ◽  
J. C. Schmitt ◽  
D. T. Anderson ◽  
M. Drevlak ◽  
...  
Keyword(s):  
Energetic Particle ◽  
Turbulent Transport ◽  
Three Dimensional ◽  
Plasma Pressure ◽  
Ion Temperature ◽  
Single Filament ◽  
Ion Temperature Gradient ◽  
Vessel Volume ◽  
Energetic Particle Transport ◽  
Particle Confinement

A new optimized quasi-helically symmetric configuration is described that has the desirable properties of improved energetic particle confinement, reduced turbulent transport by three-dimensional shaping and non-resonant divertor capabilities. The configuration presented in this paper is explicitly optimized for quasi-helical symmetry, energetic particle confinement, neoclassical confinement and stability near the axis. Post optimization, the configuration was evaluated for its performance with regard to energetic particle transport, ideal magnetohydrodynamic stability at various values of plasma pressure and ion temperature gradient instability induced turbulent transport. The effects of discrete coils on various confinement figures of merit, including energetic particle confinement, are determined by generating single-filament coils for the configuration. Preliminary divertor analysis shows that coils can be created that do not interfere with expansion of the vessel volume near the regions of outgoing heat flux, thus demonstrating the possibility of operating a non-resonant divertor.

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