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PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-9605
DTSTART:20260122T190000Z
DURATION:PT1H0M0S
DTSTAMP:20260413T102729Z
LAST-MODIFIED:20260224T190155Z
LOCATION:Sterling Hall B343
SUMMARY:Nonlinear Saturation of Ballooning Modes in Stellarators\, Pla
 sma Physics (Physics/ECE/NE 922) Seminar\, Xu Chu \, PPPL
DESCRIPTION:The nonlinear evolution and saturated states of ballooning
  modes – in particular\, metastable states – are critical for unde
 rstanding explosive MHD events in magnetic confinement fusion (MCF) de
 vices\, such as edge-localized modes (ELMs) in tokamaks and core densi
 ty collapses (CDCs) in LHD. In this work\, ballooning mode saturation 
 is investigated in realistic stellarator configurations using the flux
  tube approach of Ham et. al. [1]. The method is adapted to account fo
 r the lack of exact force balance in stellarator equilibrium solvers t
 hat assume existence of nested flux surfaces. A variational approach f
 or calculating flux tube energy is developed to overcome this force er
 ror problem in stellarator numerical equilibria. Saturated (equilibriu
 m) flux tube states that cross 10-20% of the plasma minor radius are s
 hown to exist for linearly ballooning unstable profiles. It is shown t
 hat several features of the displaced flux tube structure in a full no
 nlinear MHD simulation of Wendelstein 7X are reproduced by our model. 
 Saturated states are found in a compact stellarator equilibrium close 
 but below the marginal ballooning linear instability\, i.e. the unpert
 urbed equilibrium is metastable. This suggests that Edge-Localized-Mod
 e-like explosive MHD behavior may be possible in stellarators.<br>\n<b
 r>\n[1] Ham C J\, Cowley S C\, Brochard G and Wilson H R 2018 Plasma P
 hysics and Controlled Fusion 60 075017<br>\n
URL:https://www.physics.wisc.edu/events/?id=9605
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