Spherical Torus as an Innovative Confinement Concept

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Transport Studies in NCSX D. R. Mikkelsen For
the NCSX Research Team NCSX Research
Forum PPPL, December 7, 2006
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Overview
Goals Transport experiments in FY11 Diagnostics
needed Upgrades to enhance transport
studies Transport analysis tools Summary
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FY11 Transport-related Goals
Characterize confinement and stability
Variation with global parameters, e.g. iota,
shear, Ip, density, rotation... Comparison of
very low ripple stellarator confinement with
scalings Sensitivity to low-order
resonances Operating limits Quantify the
effects of quasi-symmetry Effect of
quasi-axisymmetry on plasma confinement Effect
of quasi-axisymmetry on rotation damping Search
for transport barriers and enhanced confinement
regimes Investigate local ion, electron, and
momentum transport
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FY11 Priorities Global Confinement
Characterize global ?E dependence
on iota magnetic shear heating
power density beta bulk ion isotope
(H,D,He) Compare to ISS-04 scaling Also
compare to tokamak L-mode scaling ITER-97P
NCSX
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Explore ?E Dependence on Iota Shear
Vacuum
Ip150 kA
Full current
Iota and magnetic shear can be varied
independently by adjusting coil
currents. Low-shear iota scan is also possible at
full current.
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Will NCSX Confinement be Sensitive to iota?
W7-AS
Search for similar behavior with low shear in
NCSX. Will this also occur with large shear?
Will H-modes occur at special iota values, as
in W7-AS?
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Effective Helical Ripple can be Scanned by
Adjusting Coil Currents
Vary effective helical ripple, look for strong
changes in momentum confinement particle
pinch Also look for changes in ExB flow
shear energy confinement profile
stiffness transport barriers Similar to HSX
studies
?eff
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Effective Ripple Should Control Rotation in NCSX
HSX biased probe drives flow
low ripple
high ripple
Modulate NBI torque in NCSX measure v? with
CHERS. DNB will decouple CHERS from torque
input.
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High Ripple can Affect Heat Transport
Ion-root 1/? regime Qhel-neo ? ?eff1.5
T4.5 Negligible for the standard
configuration. Large ripple should cause
noticeable effect. More easily seen at high
temperature.
NCSX
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Local Transport studies in FY11
Will begin studies of heat and particle
diffusivities as profile diagnostics become
available look for effect of magnetic
configuration changes. Identify regimes with
impurity accumulation. Use gas-puff source for
impurity transport studies. Compare total
bootstrap current with expected
magnitude Profile information will come from
external loops.
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Diagnostics for Transport Studies
Magnetic diagnostics provides global energy
confinement, and total bootstrap current. CHERS
(Ti) and Thomson scattering (Te, ne) local
heat- and particle-transport. CHERS toroidal
rotation for momentum transport also used to
infer radial electric field. CHERS impurity
density, SXR, and filtered cameras will be used
for impurity transport. VUV spectrometer,
bolometer and SXR will monitor impurity
accumulation.
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Upgrades to Enhance Transport StudiesCollaboratio
n Opportunities
ECH (IPP collaboration) would enable Local
electron heating, separate ion electron
channels No fast-ion driven current or
MHD Modulated heating -gt derive diffusivity
(heat pinch?) Test profile consistency - profile
stiffness Electron-root studies HIBP (possible
NIFS/RPI collaboration) would enable Direct
determination of Er Fluctuation
studies Potential and density
fluctuations Spatial correlation lengths
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Transport Analysis Tools
Magnetic analysis for Wtot and profile
mapping provides input to other analysis
tools. D. Spongs neoclassical transport module
will be used benchmarking of neoclassical
modules maturing now. Must develop standalone
neutral beam heating module several candidates
exist all need added features. Prepare for
development of a transport analysis code. find
potential modules (ORNL, PPPL, IPP, NIFS)
identify additional features needed for
NCSX Collaborative gyrokinetic studies (IPP,
NIFS, U. Md., U. Wisc., PPPL) Coordinate work to
facilitate configuration comparisons.
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FY11 results will guide NCSXs future
Characterize confinement and stability over broad
operating space. Compare NCSX confinement with
stellarator and tokamak scalings. Quantify the
effects of quasi-symmetry on ?E and
rotation. Check magnitude of bootstrap
current. Investigate local ion, electron, and
momentum transport.