Transcript Transport Studies in NCSX D. R. Mikkelsen For the NCSX Research Team

Transport Studies in NCSX
D. R. Mikkelsen
For the NCSX Research Team
NCSX PAC-8 Meeting
PPPL, Nov. 9, 2006
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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Overview
Goals
Transport experiments in FY11
Diagnostics needed
Upgrades to enhance transport studies
Transport analysis tools
Summary
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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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 rotation damping
Effect of quasi-axisymmetry on plasma confinement
Search for transport barriers and enhanced confinement regimes
Investigate local ion, electron, and momentum transport
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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FY11 Priorities: Global Confinement
With both neutral beam heating and ECH
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
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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1
.0
Explore E Dependence on Iota & Shear
Full current
0.0
0.2
0.4
0.6
Ip=150 kA
0.8
Vacuum
0.0
Norm. toroidal flux 
0.2
0.4
0.6
0.8
r2
Iota and magnetic shear can be varied independently by
adjusting coil currents.
Low shear iota scan is also possible at full current.
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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1.0
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?
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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Will NCSX Confinement Decrease with beta?
LHD
• Soft ‘equilibrium limit’ in both LHD and W7-AS:
region with good surfaces shrinks as beta rises.
• Beta ~ 3% may be available in NCSX with 3MW (FY11).
NCSX designed for large volume inside LCFS @ high .
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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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
0.05
eff
(%)
eff
(%)
0.04
0.03
Standard
0.02
0.01
0
0.2
Similar to HSX studies
0.3
0.4
0.5
0.6
0.7
Normalized toroidal flux  (r/a)
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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0.8
2
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.
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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High Ripple may Affect Heat Transport
2
Ion-root regime:
Qhel-neo  eff1.5 T4.5
Negligible for the
standard configuration.
Temperature (keV)
Te
NCSX
Ti
1
Pinj=6 MW
Ro=1.4 m B o=1.2 T
<>=4%
min. i*=0.25
ne=6x10 19 m-3
HISS-95 =2.9 HITER-97P =0.9
0
0
0.2
0.4
0.6
0.8
1
Large ripple should cause
noticeable effect.
More easily seen at high
temperature.
Power flows (MW)
5
4
Anomalous
3
2
axisymmetric
neoclassical
1
neoclassical ripple
0
0
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
0.2
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0.4
r/a
0.6
0.8
1
Local Transport studies in FY11
Will begin studies of heat and particle diffusivities; 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.
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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Diagnostics for Transport Studies
Magnetic diagnostics provide global energy confinement,
and measure total bootstrap current.
CHERS (Ti) and Thomson scattering (Te, ne) : local heat
and particle transport analysis.
CHERS toroidal rotation for momentum transport;
also used to derive radial electric field.
CHERS impurity density & SXR and filtered cameras will
be used for impurity transport.
VUV spectrometer and bolometer will monitor impurity
accumulation.
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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Upgrades to Enhance Transport Studies
Collaboration Opportunities
ECH (IPP collaboration) would enable:
Local electron heating, separate ion &electron channels
No fast-ion driven current or MHD
Modulated heating -> 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
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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Transport Analysis Tools
Equilibrium reconstruction for Wtot and mapping the profiles;
also required to provide input to other analysis tools.
D. Spong’s neoclassical transport module will be used;
benchmarking of neoclassical modules maturing now.
Develop standalone neutral beam heating module;
several candidates exist; all need added features.
Prepare for 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.
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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Summary: FY11 Goals Achievable
 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 rotation damping

Effect of quasi-axisymmetry on plasma confinement

Search for transport barriers and enhanced confinement regimes
 Investigate local ion, electron, and momentum transport
D. R. Mikkelsen, Transport Studies, NCSX PAC-8
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