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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:2
UID:UW-Physics-Event-5001
DTSTART:20190325T170500Z
DURATION:PT1H0M0S
DTSTAMP:20260419T084921Z
LAST-MODIFIED:20190311T150821Z
LOCATION:2241 Chamberlin Hall
SUMMARY:On The Interactions of Magnetic Fluctuations\, Zonal Flows\, a
 nd Microturbulence in Fusion Plasmas\, Plasma Physics (Physics/ECE/NE 
 922) Seminar\, Zach Williams\, University of Wisconsin-Madison\, Depar
 tment of Physics
DESCRIPTION:Analytic theory and gyrokinetic simulations show that turb
 ulence-regulating zonal flows are weakened by radial magnetic field fl
 uctuations as a consequence of particle streaming along radial fields 
 and shorting out cross-flux-surface potential differences. Two promine
 nt sources of radial magnetic field fluctuations are studied here\, re
 sonant magnetic perturbations (RMPs) in tokamaks and tearing modes in 
 reversed-field pinches (RFPs). This work focuses on understanding the 
 inherently multi-scale nature of the interplay of microturbulence\, zo
 nal flows\, and large-scale magnetic fluctuations and its effect on tr
 ansport. This interplay is studied with gyrokinetics to model DIII-D t
 okamak and MST RFP plasmas. An imposed magnetic perturbation that mimi
 cs a tearing mode increases the level of trapped-electron-mode turbule
 nce to a level consistent with fluctuation and transport measurements 
 in MST plasmas. This motivated a dedicated experiment on DIII-D to stu
 dy the impact of varying RMP amplitude on turbulence in inboard-limite
 d L-mode plasmas. Experimental observations demonstrate a clear depend
 ence of microturbulence levels on RMP strength. Gyrokinetic simulation
 s confirm this dependency\, and show direct connections of this behavi
 or to zonal flow degradation via magnetic fluctuations.  To approach t
 he underlying physics from a third angle\, preliminary results from si
 mulations which include a newly-incorporated current gradient drive th
 at allow for the self-consistent generation of tearing modes and their
  interactions with microinstability are presented. 
URL:https://www.physics.wisc.edu/events/?id=5001
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