Sherwood 2024

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approved	sherwood2024_abstract_staebler.pdf	2024-03-30 11:33:43	Gary Staebler

Abstracts

Author: Gary Staebler
Requested Type: Poster
Submitted: 2024-03-30 11:32:51

Co-authors: J. E. Kinsey, E. A. Belli, J. Candy

Contact Info:
ORNL
175 Whippoorwill Drive
Oak Ridge, TN   37830
United States

Abstract Text:
The linear gyrokinetic stability of drift-waves and kinetic ballooning modes in the spherical torus NSTX-U has been shown to depart significantly from conventional aspect ratio tokamaks due to the effects of parallel magnetic fluctuations. The TGLF linear gyro-fluid system of equations performs well at conventional aspect ratio but lacks sufficient perpendicular energy resolution to resolve the parallel magnetic field fluctuations. The new Gyro-Fluid System (GFS) (G. M. Staebler et al., https://doi.org/10.1063/5.0159054 ) linear stability gyro-fluid code has a flexible velocity space resolution in both parallel velocity and perpendicular energy so it is able to resolve the fully electromagnetic fluctuations. A database of CGYRO gyrokinetic linear stability calculations was built out of parameter scans around an NSTX-U standard case. The result of verifying the TGLF and GFS linear eigenvalues against this CGYRO database is presented here. It is found that, the higher resolution of the GFS code, provides significant improvement in accuracy of the linear eignvalues of both drift-waves and kinetic ballooning modes (KBM). The narrowing of the access to second stability for KBM by the parallel magnetic fluctuations is strong for the low aspect ratio NSTX-U standard case. With only perpendicular magnetic fluctuations (Bper only) both CGYRO and GFS stabilize the KBM that is unstable with fully electromagnetic fluctuations. The narrowing of the second stability access at weak magnetic shear can be important for KBM induced transport in the central core or pedestal regions of NSTX-U.

Comments:
Analytic and computational methods for modeling plasmas