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PRODID:UW-Madison-Physics-Events
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SEQUENCE:0
UID:UW-Physics-Event-4779
DTSTART:20180305T180000Z
DURATION:PT1H0M0S
DTSTAMP:20240328T134941Z
LAST-MODIFIED:20180228T210257Z
LOCATION:2241 Chamberlin Hall
SUMMARY:MHD modeling of DIII-D QH-mode discharges and comparison to ob
servations\, Plasma Physics (Physics/ECE/NE 922) Seminar\, Dr. Jacob K
ing\, Tech-X Corporation
DESCRIPTION:It is desirable to have an ITER H-mode regime that is quie
scent to edge-localized modes (ELMs). ELMs deposit large\, localized\,
impulsive\, surface heat loads that can damage the divertor. One such
regime is quiesent H-mode (QH-mode) with edge harmonic oscillations o
r broadband MHD as observed on DIII-D\, JET\, JT-60U\, and ASDEX-U [Bu
rrell et al. Phys Plasmas 2012\, Garofalo et al. Nucl Fusion 2012 and
references within]. These ELM-free discharges have the edge-plasma con
finement necessary for burning-plasma operation on ITER. QH-mode is ch
aracterized by perturbations with small toroidal-mode numbers (n '1-5
) where measurements from beam-emission spectroscopy\, electron-cyclot
ron emission\, and magnetic probe diagnostics show density\, temperatu
re and magnetic oscillations. These measurements demonstrate that the
perturbations are a saturated macroscopic mode localized within the ed
ge pedestal region. The particle transport is enhanced compared to sta
ndard H-mode discharges with ELMs\, leading to essentially steady-stat
e
\nprofiles in the pedestal region. Finally\, the operation regim
e of the QH-mode is dependent on the rotation profile\, and QH-mode di
scharges are produced with an applied torque through either coor count
er-neutral-beam injection and/or neoclassical toroidal viscosity from
plasma interaction with non-resonant magnetic fields.
\nExtended-M
HD modeling of DIII-D tokamak [J. L. Luxon\, Nucl. Fusion 42\, 614 200
2] QH-mode discharges with nonlinear NIMROD [C. R. Sovinec et al.\, JC
P 195\, 355 2004] simulations saturates into a turbulent state\, but d
oes not saturate when the steady-state flow inferred from measurements
is not included. This is consistent with the experimental observation
s of the quiescent regime on DIII-D. The simulation with flow develops
into a saturated turbulent state where the n=1 and 2 toroidal modes
become dominant through an inverse cascade. Each mode in the range of
n=1-5 is dominant at a different time. Consistent with experimental o
bservations during QH-mode\, the simulated state leads to large partic
le transport relative to the thermal transport. Analysis shows that th
e amplitude and phase of the density and temperature perturbations dif
fer resulting in greater fluctuation-induced convective particle trans
port relative to the convective thermal transport. Comparison to magne
tic-coil measurements shows rotation frequencies differ between the si
mulation and experiment which indicates that more sophisticated extend
ed-MHD two-fluid modeling is required.
\nThis work was supported b
y the DOE Office of Science (Office of Fusion Energy Sciences
URL:https://www.physics.wisc.edu/events/?id=4779
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