stanley m. kaye wayne solomon pppl, princeton university itpa naka, japan october 2007
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Supported by. Rotation & Momentum Confinement Studies in NSTX. Stanley M. Kaye Wayne Solomon PPPL, Princeton University ITPA Naka, Japan October 2007. High Rotation (M ~0.5) and Rotational Shear Observed in NSTX. - PowerPoint PPT PresentationTRANSCRIPT
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Stanley M. KayeWayne Solomon
PPPL, Princeton University
ITPANaka, JapanOctober 2007
Rotation & Momentum Confinement Studies in NSTX
Supported by
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High Rotation (M ~0.5) and Rotational Shear Observed in NSTX
• Low BT (0.35-0.55 T) operation leads to values of ExB up to the MHz range
• These ExB shear values can exceed ITG/TEM growth rates by factors of 5 to 10
Steady-state and perturbative momentum confinement studies on NSTX have started
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Local Transport Studies Reveal Sources of Energy Confinement Trends
Electrons primarily responsible forstrong BT scaling in NSTX (E~BT
0.9)
Electrons anomalous Ions near neoclassical
Variation in near-neoclassical ion transport primarily responsible for Ip scaling (E~Ip
0.4)
Neoclassical
Neoclassical levels determined from GTC-Neo: includes finite banana width effects (non-local)
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Steady-State Momentum Transport Also Can Be Determined From These Scans
No anomalous pinch necessary to explain rotation data
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Core Momentum Diffusivities Up to An Order of Magnitude Lower Than Thermal Diffusivities
Is momentum diffusivity tied more to electrondiffusivity when ions are neoclassical?
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Steady-State Does Not Scale With i As At Conventional Aspect Ratio
Due to ITG suppresson?
What is , neo?
Steady-state: from momentum balance (TRANSP) assuming no explicit pinch
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Momentum Diffusivity NOT Neoclassical Even Though Ion Thermal Diffusivity Is (~)
,neo <<
, neo can be negative!
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Inward Neoclassical Momentum Flux Driven By Ti
Relation to source of intrinsic rotation?
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Relation of and to ,neo Independent of Ion Thermal Diffusivity and Its Relation to Neoclassical
Extend analysis to i>>i,neo (L-mode)
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Dedicated Perturbative Momentum Confinement Experiments Recently Carried Out
• Use non-resonant n=3 magnetic perturbations to damp plasma rotation– Previously been used to slow plasma rotation for ITER-
relevant RWM stabilization experiments (Sabbagh et al.)
Observed rotation damping consistent with neoclassical toroidal viscosity (NTV) theory
Steady-state & transient application
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Steady-State Application of n=3 NRMP Confirms Maximum Torque at R>~1.3 m
• Delay in start of v decrease going inwards from ~1.38 m
• Beware: 10 ms time resolution
V at R=132 cm
Vat center
IRWM
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Perturbative Can be Obtained from Transient Application of nRMP
• No apparent delay in recovery of v after nRMP braking removed
R~1.15 m
R~1.32 m
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Momentum Confinement Time >>Energy Confinement Time in NSTX (Consistent with <<i)
• Use dL/dt = T – L/ relation to determine instantaneous
• Model spin-up to determine perturbative using L(t) = * [T – (T-L0/) * exp(-t/)], whereL = Angular momentumT = Torque (NB torque only)
L0 = Angular momentum at time of nRMP turn-off
Steady-state
E ~ 50 ms
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Perturbative Momentum Transport Studies Using Magnetic Braking Indicate Significant Inward Pinch
• Can determine vpinch only if , decoupled
• Assume pert, pinch
pert constant in time
• Expt’l inward pinch generally scales with theoretical estimates based on low-k turbulence-driven pinch
vPeeters= /R [-4-R/Ln](Coriolis drift)
vHahm= /R [-3](B, curvature drifts)
– Effect of off-diagonal terms (Te, ne)?
– s-s <
pert with inward pinchImportant to consider when
comparing to i
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Reasonably Good Agreement Between Theory and Experiment in Limited Comparison
Can comparisons with large variations in Ln be used to discriminate between theories?
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Varying Levels of Applied nRMP Can Probe Dynamics and Hysteresis of
Largest effect again seen for R>~1.3 m
R~1.15 m
R~1.32 m
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Discussion Points
• Main conclusions– f >>E;
pert>s-s (inward pinch significant)
– Inferred vpinch , magnitude not inconsistent with theory predictions• Will continue to run experiments over next couple of years to study
steady-state and perturbative momentum transport– Long pulse plasmas to study
s-s itself and effect on energy transport
– Multiple perturbations: use n=1 feedback, run at higher BT, lower to suppress MHD
– Apply additional torque in core: modulated beams (beam profile peaked)• Need to understand decoupling of momentum and ion energy transport
– Is this because ions are near neoclassical (i.e., ITG modes suppressed)?– Under what conditions would ITG be unstable?
• How low does ExB have to be?• Will coupling re-emerge at this point?
– Is coupled to e? Need dedicated scans• Is vpinch significant or necessary?
– Significant within data uncertainties?– Is
pert & vpinchpert a better physics description than
s-s?
• Are theories for rotation damping (e.g., NTV) applicable to ITER, CTF?– Can they be used as a basis for prediction?– What do they predict?