BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:2
UID:UW-Physics-Event-9063
DTSTART:20250127T180000Z
DTEND:20250127T191500Z
DTSTAMP:20260413T151415Z
LAST-MODIFIED:20250121T200231Z
LOCATION:1227 Engineering Hall
SUMMARY:"Optimizing a quasi-helically-symmetric stellarator for reduce
 d TEM-driven transport"\, Plasma Physics (Physics/ECE/NE 922) Seminar\
 , Michael Gerard\, University of Wisconsin - Madison
DESCRIPTION:Magnetic confinement fusion (MCF) aims to deliver a carbon
 -free energy source to meet global demands. Turbulent heat and particl
 e transport across magnetic fields remains a key challenge for MCF\, l
 imiting confinement and hence reactor performance. The 3D magnetic fie
 lds of stellarators offer a promising path forward by enabling optimiz
 ed configurations for enhanced plasma confinement. To identify novel t
 urbulence-optimization experiments that can be performed in the Helica
 lly 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 datab
 ase\, we identify ~103 configurations that preserve the neoclassical p
 roperties of the standard quasi-helically symmetric (QHS) configuratio
 n while exhibiting a broad spectrum of modified magnetic field geometr
 ies. Using the gyrokinetic code GENE\, we demonstrate that increased f
 lux-surface elongation reduces the growth rates of the trapped-electro
 n mode (TEM)—the dominant microinstability in HSX—provided quasi-h
 elical symmetry is maintained. This stabilization is attributed to geo
 metric effects that suppress destabilizing particle drifts. Quasilinea
 r modeling and nonlinear simulations\, which compare the QHS configura
 tion with a high-elongation QHS (HE-QHS) configuration\, reveal that c
 hanges in the linear growth rates fail to capture changes in the nonli
 near heat-flux between the two configurations. This discrepancy is att
 ributed 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 coup
 le 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 und
 erlying magnetic field geometry is discussed\, providing new insights 
 into TEM-driven turbulence in quasi-helically symmetric magnetic field
 s. Moreover\, preliminary results comparing the simulation data with e
 xperimental interferometry data are discussed.
URL:https://www.physics.wisc.edu/events/?id=9063
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