Plasma Physics (Physics/ECE/NE 922) Seminars |
Events During the Week of January 26th through February 2nd, 2025
Monday, January 27th, 2025
- "Optimizing a quasi-helically-symmetric stellarator for reduced TEM-driven transport"
- Time: 12:00 pm - 1:15 pm
- Place: 1227 Engineering Hall
- Speaker: Michael Gerard, University of Wisconsin - Madison
- Abstract: Magnetic confinement fusion (MCF) aims to deliver a carbon-free energy source to meet global demands. Turbulent heat and particle transport across magnetic fields remains a key challenge for MCF, limiting confinement and hence reactor performance. The 3D magnetic fields of stellarators offer a promising path forward by enabling optimized configurations for enhanced plasma confinement. To identify novel turbulence-optimization experiments that can be performed in the Helically Symmetric eXperiment (HSX) stellarator, the operational space of HSX has been explored by varying individual coil currents to produce a database of over 106 magnetohydrodynamic equilibria. From this database, we identify ~103 configurations that preserve the neoclassical properties of the standard quasi-helically symmetric (QHS) configuration while exhibiting a broad spectrum of modified magnetic field geometries. Using the gyrokinetic code GENE, we demonstrate that increased flux-surface elongation reduces the growth rates of the trapped-electron mode (TEM)—the dominant microinstability in HSX—provided quasi-helical symmetry is maintained. This stabilization is attributed to geometric effects that suppress destabilizing particle drifts. Quasilinear modeling and nonlinear simulations, which compare the QHS configuration with a high-elongation QHS (HE-QHS) configuration, reveal that changes in the linear growth rates fail to capture changes in the nonlinear heat-flux between the two configurations. This discrepancy is attributed to large-scale quasi-coherent fluctuations that appear in both configurations. Evidence is presented that suggests these large-scale modes are driven by a set of tearing-parity TEMs (TTEMs), which couple nonlinearly through the zonal flow. Moreover, the TTEMs are shown to be correlated with the appearance of micro-tearing modes, despite such modes being linearly stable. How these dynamics relate to the underlying magnetic field geometry is discussed, providing new insights into TEM-driven turbulence in quasi-helically symmetric magnetic fields. Moreover, preliminary results comparing the simulation data with experimental interferometry data are discussed.
- Host: Prof. Adelle Wright
Tuesday, January 28th, 2025
- No events scheduled
Wednesday, January 29th, 2025
- No events scheduled
Thursday, January 30th, 2025
- No events scheduled
Friday, January 31st, 2025
- No events scheduled