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Confinement and Local Transport in the National Spherical Torus Experiment (NSTX)
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 MeetingOct 16 – 21, 2006Chengdu, China
1 PPPL, Princeton University, Princeton, NJ, USA 085432 University of California, Davis, CA, USA 95616
3 IFS, University of Texas, Austin, TX, USA 787124 Nova Photonics Inc., Princeton, NJ, USA, 08540
5 ORNL, Oak Ridge, TN, USA 378316 Dept. of Applied Physics, Columbia University, NYC, NY, USA 10027
7 The Johns Hopkins University, Baltimore MD 21218
Supported byOffice ofScience
Culham Sci CtrU St. Andrews
York UChubu UFukui U
Hiroshima UHyogo UKyoto U
Kyushu UKyushu Tokai U
NIFSNiigata UU Tokyo
JAERIHebrew UIoffe Inst
RRC Kurchatov InstTRINITI
KBSIKAIST
ENEA, FrascatiCEA, Cadarache
IPP, JülichIPP, Garching
ASCR, Czech RepU Quebec
College W&MColorado Sch MinesColumbia UComp-XGeneral AtomicsINELJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UOld Dominion UORNLPPPLPSIPrinceton USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU MarylandU RochesterU WashingtonU Wisconsin
SMK – 21st IAEA 2
NSTX Addresses Transport & Turbulence Issues Critical to Both Basic Toroidal Confinement and Future Devices
• NSTX offers a novel view into plasma T&T properties– NSTX operates in a unique part of
dimensionless parameter space: R/a, T, (,
– Dominant electron heating with NBI: relevant to -heating in ITER
Major Radius R0 0.85 mAspect Ratio A 1.3Elongation 2.8Triangularity 0.8Plasma Current Ip 1.5 MAToroidal Field BT 0.55 TPulse Length 1.5 sNB Heating (100 keV) 7 MWT,tot up to 40%
– Excellent laboratory in which to study electron transport: electron transport anomalous, ions close to neoclassical
– Large range of T spanning e-s to e-m turbulence regimes
– Strong rotational shear that can influence transport
– Localized electron-scale turbulence measurable (e ~ 0.1 mm)
SMK – 21st IAEA 3
This Presentation Will Focus on Confinement & Transport Trends in NSTX and Their Underlying Processes
• Major accomplishments– Key confinement and transport dependences established (BT, Ip, , , q(r),
…)
– High priority ITPA tasks have been addressed
• Dimensionless parameter scans in Te
• Established more accurate (=a/R) scaling with NSTX (& MAST) data included in the ITPA database
98y2~Ip0.93 BT
0.15 ne0.41 P-0.69 R1.97 0.58…
new~Ip0.73 BT
0.36 ne0.39 P-0.62 R2.14 1.03 (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
SMK – 21st IAEA 4
Dimensionless Parameter Scans Have Addressed High-Priority ITPA Issues
-scan at fixed q, BT
- -dependence important to ITER advanced scenarios (B98y2~-0.9) - Factor of 2-2.5 variation in T
- Degradation of E with weak on NSTX
20% variation in e, e*
e-scan at fixed q
- Factor of >3 variation in e*
- Strong increase of confinement with decreasing collisionality
=2.1=0.6
SMK – 21st IAEA 5
Dedicated H-mode Confinement Scaling Experiments Have Isolated the BT and Ip Dependences
Scans carriedout at constantdensity, injectedpower (4 MW)
0.50 s 0.50 s
SMK – 21st IAEA 6
Dedicated H-mode Confinement Scaling ExperimentsHave Revealed Some Surprises
Strong dependence of E on BT
E,98y,2 ~ BT0.15
H98y,2 ~ 0.9 → 1.1 → 1.4
4 MW
E,98y,2 ~ Ip0.93
H98y,2 ~ 1.4 → 1.3 → 1.1
Weaker dependence on Ip
E~Ip1.3-1.5 at fixed q E,98y,2~Ip
1.1 at fixed q
NSTX E exhibits strong scaling at fixed q
4 MW
SMK – 21st IAEA 7
Variation of Electron Transport Primarily Responsible for BT Scaling
Broadening of Te & reduction in e outside r/a=0.5 with increasing BT
Ions near neoclassical
Neoclassical
SMK – 21st IAEA 8
Theory/Gyrokinetic Calculations Suggest ETG May Play an Important Role in Determining Electron Transport at Low BT
Non-linear simulations indicate formation of radial streamers (up to 200e): FLR-modified fluid code [Horton et al., PoP 2005]
• Good agreement between experimental and theoretical saturated transport level at 0.35 T
• Experimental e profile consistent with that predicted by e-m ETG theory [Horton et al., NF 2004] at 0.35 T
• Not at higher BT
Kim, IFS
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
0.35 T
GS2
SMK – 21st IAEA 9
Ion Transport Primarily Governs Ip Scaling- Ions Near Neoclassical Level -
i,GTC-NEO
(r/a=0.5-0.8)
GTC-Neo neoclassical: includes finite banana width effects (non-local)
SMK – 21st IAEA 10
Turbulence Measurements + Gyrokinetic Calculations Have Helped Identify Possible Sources of Transport
Ion transport duringH-phase isneoclassical
Microwave scattering system measuresreduced fluctuations (n/n) in both upperITG/TEM and ETG ranges during H-mode
~
Electron transportreduced, but remainsanomalous
Ion and electron transport changegoing from L- to H-modes
- Localized measurement (axis to edge)- Excellent radial resolution (6 cm)
ELMs
SMK – 21st IAEA 11
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
Experimental e profile consistentwith that predicted by e-s ETG theory(Horton et al, Phys. Plasmas [2004])
Non-linear GTC resultsindicate ITG modesstable during H-phase;i ~ neoclassical
SMK – 21st IAEA 12
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 T scalings
– No degradation of BE with T
• n/n decreases from L- to H-phase for kr=2 to 24 cm-1 (upper ITG/TEM to ETG range) – Associated with reduction in transport
• Linear and non-linear theory have indicated ETG modes could be important– Need also to consider lower-k modes
(microtearing, ITG/TEM)
~
SMK – 21st IAEA 13
Backup Vugraphs
SMK – 21st IAEA 14
New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes
12 channel MSE [NOVA Photonics]
LRDFITReconstruction
Rmag
51-point CHERS 20-point MPTS
Tangential microwave scattering measureslocalized electron-scale turbulence
• kr=2 (upper ITG/TEM) to ~24 (ETG) cm-1
• e ~0.01 cm• r ~ 6 cm• k ~ 1 cm-1
• Can vary location of scattering volume (near Rmag to near edge)
Important for equilibrium and microinstability calculations
SMK – 21st IAEA 15
New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes
Tangential micorwave scattering measureslocalized electron-scale turbulence
12 channel MSE [NOVA Photonics]
LRDFITReconstruction
Important for equilibrium and microinstability calculations
• kr=2 (upper ITG/TEM) to ~24 (ETG) cm-1
• e ~0.01 cm• r ~ 6 cm• k ~ 1 cm-1
• Can vary location of scattering volume (near Rmag to near edge)
SMK – 21st IAEA 16
Dimensionless Variable Scans Have Addressed HighPriority ITPA Physics Issues (- scaling)
-scan at fixed e, e*
- -dependence important to ITER advanced scenarios (B98y2~-0.9) - Degradation of E with weak on NSTX
NSTX data used in conjunction with ITPA data to establish (=a/Rscaling with more confidence
ITER98PB(y,2) scaling does not represent low R/a data well
98y2~Ip0.93BT
0.15ne0.41P-0.69R1.970.58…
new~Ip0.73BT
0.36ne0.39P-0.62R2.141.03
(Kaye et al., PPCF 48 [2006] A429) 2-2.5 variation in T
20% variation in e, e*
SMK – 21st IAEA 17
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
SMK – 21st IAEA 18
Pellet Perturbations Are Being Used to Probe Relation of Critical Gradient Physics to q-Profile
H-mode with monotonic q-profile exhibits stiff profile behavior → Te close to marginal stability
Reversed magnetic shear L-mode responds to pellet perturbationover several ms
Soft X-ray arraydiagnoses fast Te
R/LTe
t=297→301 ms
R/LTe
t=440→444 ms
Stutman, JHU