Linearized model Fokker–Planck collision operators for gyrokinetic simulations. II. Numerical implementation and tests

Barnes, Michael; Abel, Ian; Dorland, W.; Ernst, D. R.; Hammett, G. W.; Ricci, Paolo; Rogers, B. N.; Schekochihin, A. A.; Tatsuno, T.

doi:10.1063/1.3155085

Cited by 96 publications

(157 citation statements)

References 47 publications

Supporting

Mentioning

155

Contrasting

Order By: Relevance

“…The poloidal wave vectors shown below have zero radial component, which were always found to be the most unstable mode. Simulations benchmarked against GYRO were in the collisionless regime, while collisional simulations were computed only with the GS2 code, as it implements a recently developed collisional operator that conserves particles, energy and momentum [41]. The need of this advanced collision operator was dictated by the high values of collisionality ν * that, at the top of the pedestal, are greater than one.…”

Section: Gyrokinetic Modelingmentioning

confidence: 99%

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

et al. 2015

View full text Add to dashboard Cite

Abstract. The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as Weakly Coherent Modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-modelike profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the Phase Contrast Imaging diagnostic during Imode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes nonmonotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km/s. However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in the pedestal region with the GS2 code and its recently upgraded model collision operator that conserves particles, energy and momentum. The increased bootstrap current and flow shear generated by the temperature pedestal are shown to decrease growth rates, thus possibly generating a feedback mechanism that progressively stabilizes fluctuations.

show abstract

Section: Gyrokinetic Modelingmentioning

confidence: 99%

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

et al. 2015

View full text Add to dashboard Cite

show abstract

“…The velocity distribution is resolved on a grid in energy E = v 2 /2 and pitch angle λ = v 2 ⊥ /v 2 space, with the points selected on a Legendre polynomial basis. A fully conservative, linearized, gyroaveraged collision operator is employed (Abel et al 2008;Barnes et al 2009). …”

Section: Gyrokinetic Simulations Of Low-frequency Turbulencementioning

confidence: 99%

Diagnosing collisionless energy transfer using field–particle correlations: gyrokinetic turbulence

2017

View full text Add to dashboard Cite

Determining the physical mechanisms that extract energy from turbulent fluctuations in weakly collisional magnetized plasmas is necessary for a more complete characterization of the behaviour of a variety of space and astrophysical plasmas. Such a determination is complicated by the complex nature of the turbulence as well as observational constraints, chiefly that in situ measurements of such plasmas are typically only available at a single point in space. Recent work has shown that correlations between electric fields and particle velocity distributions constructed from single-point measurements produce a velocity-dependent signature of the collisionless damping mechanism. We extend this work by constructing field-particle correlations using data sets drawn from single points in strongly driven, turbulent, electromagnetic gyrokinetic simulations to demonstrate that this technique can identify the collisionless mechanisms operating in such systems. The velocity-space structure of the correlation between proton distributions and parallel electric fields agrees with expectations of resonant mechanisms transferring energy collisionlessly in turbulent systems. This work motivates the eventual application of field-particle correlations to spacecraft measurements in the solar wind, with the ultimate goal to determine the physical mechanisms that dissipate magnetized plasma turbulence.

show abstract

“…Spatial dimensions ( ) x y , perpendicular to the mean field are treated pseudospectrally; an upwind finite-difference scheme is used in the parallel direction, z. Collisions employ a fully conservative, linearized collision operator with energy diffusion and pitch-angle scattering (Abel et al 2008;Barnes et al 2009). …”

Section: Strong Alfvén Wave Collision Simulationsmentioning

confidence: 99%

The Dynamical Generation of Current Sheets in Astrophysical Plasma Turbulence

Howes

2016

ApJL

View full text Add to dashboard Cite

Turbulence profoundly affects particle transport and plasma heating in many astrophysical plasma environments, from galaxy clusters to the solar corona and solar wind to Earthʼs magnetosphere. Both fluid and kinetic simulations of plasma turbulence ubiquitously generate coherent structures, in the form of current sheets, at small scales, and the locations of these current sheets appear to be associated with enhanced rates of dissipation of the turbulent energy. Therefore, illuminating the origin and nature of these current sheets is critical to identifying the dominant physical mechanisms of dissipation, a primary aim at the forefront of plasma turbulence research. Here, we present evidence from nonlinear gyrokinetic simulations that strong nonlinear interactions between counterpropagating Alfvén waves, or strong Alfvén wave collisions, are a natural mechanism for the generation of current sheets in plasma turbulence. Furthermore, we conceptually explain this current sheet development in terms of the nonlinear dynamics of Alfvén wave collisions, showing that these current sheets arise through constructive interference among the initial Alfvén waves and nonlinearly generated modes. The properties of current sheets generated by strong Alfvén wave collisions are compared to published observations of current sheets in the Earthʼs magnetosheath and the solar wind, and the nature of these current sheets leads to the expectation that Landau damping of the constituent Alfvén waves plays a dominant role in the damping of turbulently generated current sheets.

show abstract

Linearized model Fokker–Planck collision operators for gyrokinetic simulations. II. Numerical implementation and tests

Cited by 96 publications

References 47 publications

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

Diagnosing collisionless energy transfer using field–particle correlations: gyrokinetic turbulence

The Dynamical Generation of Current Sheets in Astrophysical Plasma Turbulence

Contact Info

Product

Resources

About