Transcript Neoclassical tearing mode onset in NSTX E D Fredrickson , J Menard

Supported by
Neoclassical tearing mode
onset in NSTX
E D Fredricksona, J Menarda,
D. Stutmanb, K. Tritzb
a
b
Princeton Plasma Physics Laboratory, NJ
Johns Hopkins University, MD
46th Annual Meeting of the Division of Plasma
Physics, American Physical Society
15 – 19 November 2004
Savannah, Georgia
Columbia U
Comp-X
General Atomics
INEL
Johns Hopkins U
LANL
LLNL
Lodestar
MIT
Nova Photonics
NYU
ORNL
PPPL
PSI
SNL
UC Davis
UC Irvine
UCLA
UCSD
U Maryland
U Rochester
U Washington
U Wisconsin
Culham Sci Ctr
Hiroshima U
HIST
Kyushu Tokai U
Niigata U
Tsukuba U
U Tokyo
JAERI
Ioffe Inst
TRINITI
KBSI
KAIST
ENEA, Frascati
CEA, Cadarache
IPP, Jülich
IPP, Garching
U Quebec
Sawtooth crashes often trigger modes
which appear similar to NTMs
• Toroidal mode number of
n = 2 suggests NTM.
• Strong interaction with
sawtooth instability, drop
in amplitude at sawtooth.
• Can amplitude evolution
be modeled with extended
Rutherford equation?
• "Spontaneous" n = 2
modes are also seen.
Amplitude drop at sawteeth not
predicted by Rutherford equation
• Amplitude evolution of 3/2
modeled with Rutherford
equation, TRANSP.
• "NTM" coefficients adjusted
to match Mirnov amplitude.
• Local parameters not affected
by sawtooth crash - island
width should evolve on
resistive time scale.
• Need internal measurements.
Early in sawtooth period n=2 is
kink-like, strong n=1 mode
0.430 s
0.446 s
Minor Radius (cm)
0
• Weakly phase
locked with 3:2
frequency match.
• n=2 not triggered
20
through non-linear
coupling to n=1.
• Are core oscillations
a chord-integral
40
effect?
0.4 ms
0.4 ms
• Sawtooth crash
• Insufficient data for tomography,
triggers n=2 kink?
use simulations.
Equilibrium J, q profiles are used to
simulate 3/2 tearing mode
• Soft x-ray data Abel
inverted on EFIT grid to
find local emissivity.
• Emissivity remapped on
island flux plot and chord
integrated.
• Comparison to fluctuation
amplitude in experimental
data is used to constrain
island size, eigenmode
structure.
Simulation suggests 2/2 persists in
core, as at high aspect ratio
• Core oscillation's
phase pattern,
amplitude differs
from simulation.
• Coupling to 2/2
mode may reduce
classic D' of 3/2
mode.
• Or is this a 2/2
island?
• q profile is not measured, adjusted
to match phase inversion.
The inferred q=1 radius is comparable
to the inferred q=1.5 radius
Time (s)
- q = 1.5 radius?
- q = 1 radius
SXI Inversion
Tangency Radius (cm)
• The q=1.5
• Radius of q=1 surface is ≈1.2 times
radius was
the chord integrated inversion radius
40
inferred from
simulating the
20
island inversion
radius.
0
• Could these
n = 2 modes be
-20
2/2 kinks
evolving to 2/2
-40
0.4255
0.4265
islands?
Summary
• Studies of NTM onset in NSTX raise more
questions than are answered.
• NTMs interact much more strongly with
sawteeth than should be expected.
• SXI implies islands near q = 1 surface, i.e.,
islands are not 3/2 modes.
• Routine current profile measurements expected
for next campaign; are key to progress.