Velocity-space resolution, entropy production, and upwind dissipation in Eulerian gyrokinetic simulations

Candy, J; Waltz, R E

doi:10.1063/1.2184069

Title: Velocity-space resolution, entropy production, and upwind dissipation in Eulerian gyrokinetic simulations

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Abstract

Equations which describe the evolution of volume-averaged gyrokinetic entropy are derived and added to GYRO [J. Candy and R.E. Waltz, J. Comput. Phys. 186, 545 (2003)], a Eulerian gyrokinetic turbulence simulation code. In particular, the creation of entropy through spatial upwind dissipation (there is zero velocity-space dissipation in GYRO) and the reduction of entropy via the production of fluctuations are monitored in detail. This new diagnostic has yielded several key confirmations of the validity of the GYRO simulations. First, fluctuations balance dissipation in the ensemble-averaged sense, thus demonstrating that turbulent GYRO simulations achieve a true statistical steady state. Second, at the standard spatial grid size, neither entropy nor energy flux is significantly changed by a 16-fold increase (from 32 to 512 grid points per cell) in the number of grid points in the two-dimensional velocity space. Third, the measured flux is invariant to an eightfold increase in the upwind dissipation coefficients. A notable conclusion is that the lack of change in entropy with grid refinement refutes the familiar but incorrect notion that Eulerian gyrokinetic codes miss important velocity-space structure. The issues of density and energy conservation and their relation to negligible second-order effects such as the parallel nonlinearity are alsomore » discussed.« less

Authors:

Candy, J; Waltz, R E ^[1]

General Atomics, San Diego, California 92121 (United States)

Publication Date:: Wed Mar 15 00:00:00 EST 2006

OSTI Identifier:: 20782553

Resource Type:: Journal Article

Journal Name:: Physics of Plasmas

Additional Journal Information:: Journal Volume: 13; Journal Issue: 3; Other Information: DOI: 10.1063/1.2184069; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X

Country of Publication:: United States

Language:: English

Subject:: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CHARGED-PARTICLE TRANSPORT; ENERGY CONSERVATION; ENTROPY; FLUCTUATIONS; NONLINEAR PROBLEMS; PLASMA; PLASMA SIMULATION; SPACE; STEADY-STATE CONDITIONS; THERMODYNAMICS; TURBULENCE; TWO-DIMENSIONAL CALCULATIONS; VELOCITY

Citation Formats


                    Candy, J, and Waltz, R E. Velocity-space resolution, entropy production, and upwind dissipation in Eulerian gyrokinetic simulations.  United States: N. p., 2006. 
        Web.  doi:10.1063/1.2184069.

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                    Candy, J, & Waltz, R E. Velocity-space resolution, entropy production, and upwind dissipation in Eulerian gyrokinetic simulations.  United States.  https://doi.org/10.1063/1.2184069

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                    Candy, J, and Waltz, R E. 2006.  
        "Velocity-space resolution, entropy production, and upwind dissipation in Eulerian gyrokinetic simulations".  United States.  https://doi.org/10.1063/1.2184069.

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@article{osti_20782553,

  title        = {Velocity-space resolution, entropy production, and upwind dissipation in Eulerian gyrokinetic simulations},

  author       = {Candy, J and Waltz, R E},

  abstractNote = {Equations which describe the evolution of volume-averaged gyrokinetic entropy are derived and added to GYRO [J. Candy and R.E. Waltz, J. Comput. Phys. 186, 545 (2003)], a Eulerian gyrokinetic turbulence simulation code. In particular, the creation of entropy through spatial upwind dissipation (there is zero velocity-space dissipation in GYRO) and the reduction of entropy via the production of fluctuations are monitored in detail. This new diagnostic has yielded several key confirmations of the validity of the GYRO simulations. First, fluctuations balance dissipation in the ensemble-averaged sense, thus demonstrating that turbulent GYRO simulations achieve a true statistical steady state. Second, at the standard spatial grid size, neither entropy nor energy flux is significantly changed by a 16-fold increase (from 32 to 512 grid points per cell) in the number of grid points in the two-dimensional velocity space. Third, the measured flux is invariant to an eightfold increase in the upwind dissipation coefficients. A notable conclusion is that the lack of change in entropy with grid refinement refutes the familiar but incorrect notion that Eulerian gyrokinetic codes miss important velocity-space structure. The issues of density and energy conservation and their relation to negligible second-order effects such as the parallel nonlinearity are also discussed.},

  doi          = {10.1063/1.2184069},

  url          = {https://www.osti.gov/biblio/20782553},
  journal      = {Physics of Plasmas},

  issn         = {1070-664X},

  number       = 3,

  volume       = 13,

  place        = {United States},

  year         = {Wed Mar 15 00:00:00 EST 2006},

  month        = {Wed Mar 15 00:00:00 EST 2006}

}

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