A statistical study of gyro-averaging effects in a reduced model of drift-wave transport

Fonseca, J. D. da; Del-Castillo-Negrete, Diego B; Sokolov, Igor M.; Caldas, Iberê L.

doi:10.1063/1.4961430

Cited by 3 publications

(2 citation statements)

References 22 publications

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“…Following da Fonseca et al. (2016), in this figure we plot the fraction of trapped particles (i.e. not reaching the surface) as function of the amplitude .…”

Section: Non-diffusive Transport Due To Flr Effectsmentioning

confidence: 99%

“…However, the transport along the flow direction has a superdiffusive scaling and increases with the Larmor radius. More recently, FLR effects have been studied in the context of Hamiltonian map models of transport in monotonic and non-monotonic flows with a continuum spectrum of drift waves with a one-dimensional spatial structure (da Fonseca, del Castillo-Negrete & Caldas 2014;da Fonseca et al 2016).…”

Section: Introductionmentioning

confidence: 99%

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Finite Larmor radius effects on weak turbulence transport

2018

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Transport of test particles in two-dimensional weak turbulence with waves propagating along the poloidal direction is studied using a reduced model. Finite Larmor radius (FLR) effects are included by gyroaveraging over one particle orbit. For low wave amplitudes the motion is mostly regular with particles trapped in the potential wells. As the amplitude increases the trajectories become chaotic and the Larmor radius modifies the orbits. For a thermal distribution of Finite Larmor radii the particle distribution function (PDF) is Gaussian for small $\unicode[STIX]{x1D70C}_{th}$ (thermal gyroradius) but becomes non-Gaussian for large $\unicode[STIX]{x1D70C}_{th}$. However, the time scaling of transport is diffusive, as characterized by a linear dependence of the variance of the PDF with time. An explanation for this behaviour is presented that provides an expression for an effective diffusion coefficient and reproduces the numerical results for large wave amplitudes which implies generalized chaos. When a shear flow is added in the direction of wave propagation, a modified model is obtained that produces free-streaming particle trajectories in addition to trapped ones; these contribute to ballistic transport for low wave amplitude but produce super-ballistic transport in the chaotic regime. As in the previous case, the PDF is Gaussian for low $\unicode[STIX]{x1D70C}_{th}$ becoming non-Gaussian as it increases. The perpendicular transport presents the same behaviour as in the case with no flow but the diffusion is faster in the presence of the flow.

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“…Following da Fonseca et al. (2016), in this figure we plot the fraction of trapped particles (i.e. not reaching the surface) as function of the amplitude .…”

Section: Non-diffusive Transport Due To Flr Effectsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Finite Larmor radius effects on weak turbulence transport

2018

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Larmor radius effect on the control of chaotic transport in tokamaks

Osorio-Quiroga,

Roberto,

Viana

et al. 2024

Physics of Plasmas

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We investigate the influence of the finite Larmor radius on the dynamics of guiding-center test particles subjected to an E×B drift in a large aspect-ratio tokamak. For that, we adopt the drift-wave test particle transport model presented by Horton et al. [Phys. Plasmas 5, 3910 (1998)] and introduce a second-order gyro-averaged extension, which accounts for the finite Larmor radius effect that arises from a spatially varying electric field. Using this extended model, we numerically examine the influence of the finite Larmor radius on chaotic transport and the formation of transport barriers. For non-monotonic plasma profiles, we show that the twist condition of the dynamical system, i.e., KAM theorem's non-degeneracy condition for the Hamiltonian, is violated along a special curve, which, under non-equilibrium conditions, exhibits significant resilience to destruction, thereby inhibiting chaotic transport. This curve acts as a robust barrier to transport and is usually called shearless transport barrier. While varying the amplitude of the electrostatic perturbations, we analyze bifurcation diagrams of the shearless barriers and escape rates of orbits to explore the impact of the finite Larmor radius on controlling chaotic transport. Our findings show that increasing the Larmor radius enhances the robustness of transport barriers, as larger electrostatic perturbation amplitudes are required to disrupt them. Additionally, as the Larmor radius increases, even in the absence of transport barriers, we observe a reduction in the escape rates, indicating a decrease in chaotic transport.

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