Abstract Details
Abstracts
Author: Minglei Yang
Requested Type: Poster
Submitted: 2025-02-27 10:07:42
Co-authors: Jason Parisi, Gary Staebler
Contact Info:
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, TN 37831
USA
Abstract Text:
The linear stability of the H-mode pedestal in NSTX-U was extensively explored in previous work [1] using the CGYRO gyrokinetic code [2]. In the present work, this large database of CGYRO runs is used to verify the Gyro-Fluid-System (GFS [3]) of linear gyrokinetic moment equations for use in the extreme plasma conditions of the NSTX-U pedestal. The optimum accuracy of GFS is found for several choices of the number of parallel velocity (Nu) and perpendicular energy (Ne) moments in GFS. A Bayesian sampling method is used to find the optimum Gaussian measure width (Wz) and number of Hermite polynomials (Nz) for the linear eigenmodes for several velocity resolutions. The best results for GFS were found for very low velocity resolution (Ne=2, Nu=3). The high collision frequency in the NSTX-U pedestal smooths the velocity space reducing the required number of moments. The linear GFS code is fast enough to compute the kinetic ballooning mode (KBM) stability for use in the EPED model for the pedestal structure [4]. Good agreement between GFS and CGYRO was also found for TEM cases. Local quasi-linear transport simulations of the pedestal region could be performed with GFS. A minimum of Ne=3 is required in order to compute the Reynolds stress due to parallel magnetic field flutter. Higher parallel velocity resolution (Nu=5) is then required. The best resolution found for core tokamak conditions [3] is: Ne=3, Nu=7 and Wz=1.74, Nz=12. This resolution has also been shown to be sufficient for the linear stability of drift-waves and KBM in the core of NSTX-U [5].
[1] J. F. Parisi, et al., Nucl. Fusion 64 (2024) 054002.
[2] J. Candy, et al., J. Comput. Phys. 324 (2016) 73.
[3] G. M. Staebler, et al., Phys. Plasmas 30 (2023) 102501.
[4] P. Snyder, et al., Nucl. Fusion 49 (2009) 085035.
[5] J. E. Kinsey, et al., submitted to Phys. Plasmas.
Characterization: 1.0
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