Confinement and Local Transport in the National Spherical Torus Experiment (NSTX)

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Confinement and Local Transport in the National
Spherical Torus Experiment (NSTX)
College WM Colorado Sch Mines Columbia
U Comp-X General Atomics INEL Johns Hopkins
U LANL LLNL Lodestar MIT Nova Photonics New York
U Old Dominion U ORNL PPPL PSI Princeton
U SNL Think Tank, Inc. UC Davis UC
Irvine UCLA UCSD U Colorado U Maryland U
Rochester U Washington U Wisconsin
Stanley M. Kaye1, M.G. Bell1, R.E. Bell1, C. W.
Domier2, W. Horton3, J. Kim3, B.P. LeBlanc1, F.
Levinton4,N.C. Luhmann2, R. Maingi5, E.
Mazzucato1, J.E. Menard1, D.R. Mikkelsen1, H.
Park1, G. Rewoldt1, S.A. Sabbagh6, D. Smith1, D.
Stutman7, K. Tritz7, W. Wang1, H. Yuh4 21st
IAEA/Fusion 2006 Meeting Oct 16 21,
2006 Chengdu, China 1 PPPL, Princeton
University, Princeton, NJ, USA 08543 2 University
of California, Davis, CA, USA 95616 3 IFS,
University of Texas, Austin, TX, USA 78712 4 Nova
Photonics Inc., Princeton, NJ, USA, 08540 5 ORNL,
Oak Ridge, TN, USA 37831 6 Dept. of Applied
Physics, Columbia University, NYC, NY, USA
10027 7 The Johns Hopkins University, Baltimore
MD 21218
Culham Sci Ctr U St. Andrews York U Chubu U Fukui
U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu
Tokai U NIFS Niigata U U Tokyo JAERI Hebrew
U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST
ENEA, Frascati CEA, Cadarache IPP, Jülich IPP,
Garching ASCR, Czech Rep U Quebec
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NSTX Addresses Transport Turbulence Issues
Critical to Both Basic Toroidal Confinement and
Future Devices

• NSTX offers a novel view into plasma TT
  properties
• NSTX operates in a unique part of dimensionless
  parameter space R/a, bT, (r, n)
• Dominant electron heating with NBI relevant to
  a-heating in ITER

• Excellent laboratory in which to study electron
  transport electron transport anomalous, ions
  close to neoclassical
• Large range of bT spanning e-s to e-m turbulence
  regimes
• Strong rotational shear that can influence
  transport
• Localized electron-scale turbulence measurable
  (re 0.1 mm)

Major Radius R0 0.85 m Aspect Ratio
A 1.3 Elongation k 2.8 Triangularity
d 0.8 Plasma Current Ip 1.5 MA Toroidal Field
BT 0.55 T Pulse Length 1.5 s NB Heating (100
keV) 7 MW bT,tot up to 40
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This Presentation Will Focus on Confinement
Transport Trends in NSTX and Their Underlying
Processes

• Major accomplishments
• Key confinement and transport dependences
  established (BT, Ip, b, n, q(r),)
• High priority ITPA tasks have been addressed
• Dimensionless parameter scans in bT, ne
• Established more accurate e (a/R) scaling with
  NSTX ( MAST) data included in the ITPA database
• t98y2Ip0.93 BT0.15 ne0.41 P-0.69 R1.97 e0.58
• tnewIp0.73 BT0.36 ne0.39 P-0.62 R2.14 e1.03
  (Kaye et al., PPCF 48 2006 A429)
• Localized turbulence characteristics being
  assessed across wide range of k (upper ITG/TEM to
  ETG)
• Theory/simulations have indicated ETG modes could
  be important in controlling electron transport

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Dimensionless Parameter Scans Have Addressed
High-Priority ITPA Issues
b-scan at fixed q, BT - b-dependence important
to ITER advanced scenarios (Bt98y2b-0.9)
- Factor of 2-2.5 variation in bT - Degradation
of tE with b weak on NSTX
ne-scan at fixed q - Factor of gt3 variation in
ne - Strong increase of confinement with
decreasing collisionality
20 variation in re, ne
k2.1 d0.6
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Dedicated H-mode Confinement Scaling Experiments
Have Isolated the BT and Ip Dependences
Scans carried out at constant density,
injected power (4 MW)
0.50 s
0.50 s
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Dedicated H-mode Confinement Scaling
ExperimentsHave Revealed Some Surprises
Strong dependence of tE on BT
Weaker dependence on Ip
H98y,2 0.9 ? 1.1 ? 1.4
H98y,2 1.4 ? 1.3 ? 1.1
4 MW
4 MW
tE,98y,2 BT0.15
tE,98y,2 Ip0.93
NSTX tE exhibits strong scaling at fixed q
tEIp1.3-1.5 at fixed q
tE,98y,2Ip1.1 at fixed q
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Variation of Electron Transport Primarily
Responsible for BT Scaling
Broadening of Te reduction in ce outside
r/a0.5 with increasing BT
Ions near neoclassical
Neoclassical
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Theory/Gyrokinetic Calculations Suggest ETG May
Play an Important Role in Determining Electron
Transport at Low BT
ETG linearly unstable only at lowest BT - 0.35
T R/LTe 20 above critical gradient - 0.45,
0.55 T R/LTe 20-30 below critical gradient
Non-linear simulations indicate formation of
radial streamers (up to 200re) FLR-modified
fluid code Horton et al., PoP 2005
GS2
0.35 T
Kim, IFS

• Good agreement between experimental and
  theoretical saturated transport level at 0.35 T
• Experimental ce profile consistent with that
  predicted by e-m ETG theory Horton et al., NF
  2004 at 0.35 T
• Not at higher BT

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Ion Transport Primarily Governs Ip Scaling- Ions
Near Neoclassical Level -
GTC-Neo neoclassical includes finite banana
width effects (non-local)
ci,GTC-NEO (r/a0.5-0.8)
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Turbulence Measurements Gyrokinetic
Calculations Have Helped Identify Possible
Sources of Transport
Ion and electron transport change going from L-
to H-modes
Electron transport reduced, but remains anomalous
Ion transport during H-phase is neoclassical
- Localized measurement (axis to edge) -
Excellent radial resolution (6 cm)
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Theory/Gyrokinetic Calculations Indicate Both
ITG/TEM and ETG are Possible Candidates for
Electron Transport
GS2 calculations indicate lower linear growth
rates at all wavenumbers during H- than during
L-phase ETG unstable
Non-linear GTC results indicate ITG modes stable
during H-phase ci neoclassical
Experimental ce profile consistent with that
predicted by e-s ETG theory (Horton et al, Phys.
Plasmas 2004)
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NSTX Plays a Key Role in Multi-Scale Transport
Turbulence Research

• Confinement and transport trends found to differ
  from those at higher R/a
• Strong BT, weaker Ip scaling
• Electron transport variation primarily
  responsible for BT scaling
• Ions near neoclassical primarily responsible for
  Ip scaling
• Understand the source of the difference in
  confinement trends at different R/a (low vs
  high-k turbulence dominant at different R/a, BT?)
• Data provided to ITPA H-mode database for R/a and
  bT scalings
• No degradation of BtE with bT

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Backup Vugraphs
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New Diagnostic Capabilities Have Facilitated
Progress in Understanding Transport Processes
12 channel MSE NOVA Photonics
51-point CHERS
20-point MPTS
LRDFIT Reconstruction
Rmag
Important for equilibrium and microinstability
calculations
Tangential microwave scattering
measures localized electron-scale turbulence

• kr2 (upper ITG/TEM) to 24 (ETG) cm-1
• re 0.01 cm
• Dr 6 cm
• Dk 1 cm-1
• Can vary location of scattering volume
• (near Rmag to near edge)

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New Diagnostic Capabilities Have Facilitated
Progress in Understanding Transport Processes
Tangential micorwave scattering
measures localized electron-scale turbulence
12 channel MSE NOVA Photonics

• kr2 (upper ITG/TEM) to 24 (ETG) cm-1
• re 0.01 cm
• Dr 6 cm
• Dk 1 cm-1
• Can vary location of scattering volume
• (near Rmag to near edge)

Important for equilibrium and microinstability
calculations
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Dimensionless Variable Scans Have Addressed
HighPriority ITPA Physics Issues (e, b - scaling)
b-scan at fixed re, ne - b-dependence
important to ITER advanced scenarios
(Bt98y2b-0.9) - Degradation of tE with b weak
on NSTX
ITER98PB(y,2) scaling does not represent low R/a
data well
20 variation in re, ne
NSTX data used in conjunction with ITPA data to
establish e (a/R) scaling with more confidence
t98y2Ip0.93BT0.15ne0.41P-0.69R1.97e0.58
tnewIp0.73BT0.36ne0.39P-0.62R2.14e1.03
(Kaye et al., PPCF 48 2006 A429)
2-2.5 variation in bT
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Stronger Reversed Magnetic Shear Is Associated
with Reduced Transport
Weak vs Reverse-Shear L-mode
Global non-linear GTC and GYRO simulations show
that a pure ITG mode is unstable without ExB flow
shear included
TEM ETG calculations underway
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Pellet Perturbations Are Being Used to Probe
Relation of Critical Gradient Physics to q-Profile
Soft X-ray array diagnoses fast DTe
R/LTe t440?444 ms
H-mode with monotonic q-profile exhibits stiff
profile behavior ? Te close to marginal
stability
R/LTe t297?301 ms
Reversed magnetic shear L-mode responds to pellet
perturbation over several ms
Stutman, JHU