April 4-6

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Author: Patrick S. Kim
Requested Type: Poster
Submitted: 2022-03-03 22:37:18

Co-authors: W. Dorland, R. Jorge

Contact Info:
8279 Paint Branch Dr
College Park, MD   20852
United States

Abstract Text:
Reducing turbulent transport in stellarators is challenging since it requires computationally expensive turbulence codes that in turn require numerical equilibrium codes to generate the three-dimensional magnetic geometry. This makes the workflow too prohibitively expensive to use in optimization loops given the stellarator's large parameter space. Here, the near-axis expansion is used to calculate geometric parameters [1] needed as inputs for the gyrokinetic codes GX [2] and GS2 [3]. These codes are then used for nonlinear simulations of the turbulent heat flux for quasisymmetric stellarators like NCSX. The near-axis expansion is an expansion in powers of the inverse aspect ratio about the magnetic axis that can be used to directly construct quasisymmetric stellarator geometries without needing equilibrium codes such as VMEC. Thus, using the near-axis expansion to analytically calculate the geometric inputs offers a method of setting up turbulence simulations that is much computationally faster than using equilibrium codes. GX is a new pseudo-spectral gyrokinetic code implemented on GPU's that allows running simulations with less velocity resolution and newer hardware. These nonlinear simulations serve to perform cross-code verification of GX and GS2 using geometries constructed using the near-axis expansion.
[1] R. Jorge and M. Landreman, “The use of near-axis magnetic fields for stellarator turbulence simulations, ”Plasma Physics and Controlled Fusion", vol. 63, no. 1, p. 014001, 2021.
[2] N. R. Mandell, W. Dorland, and M. Landreman, “Laguerre-Hermite pseudo-spectral velocity formulation of gyrokinetics,” J. Plasma Phys, vol. 84, no. 1, p. 905 840108, 2018.
[3] J. A. Baumgaertel, E. A. Belli, W. Dorland,et al., “Simulating gyrokinetic microinstabilities in stellarator geometry with GS2,” Physics of Plasmas, vol. 18, no. 12, p. 122 301, 2011.