1. 21st IAEA/Fusion 2006 Meeting
Supported by
Office of
Science
Confinement and Local Transport in the National Spherical Torus Experiment (NSTX)
College W&M
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

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, 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 R m
Aspect Ratio A 1.3
Elongation k 2.8
Triangularity d 0.8
Plasma Current Ip 1.5 MA
Toroidal Field BT T
Pulse Length 1.5 s
NB Heating (100 keV) 7 MW
bT,tot up to 40%
SMK – 21st IAEA 2

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, 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
t98y2~Ip0.93 BT0.15 ne0.41 P-0.69 R1.97 e0.58…
tnew~Ip0.73 BT0.36 ne0.39 P-0.62 R2.14 e (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 3

4. Dimensionless Parameter Scans Have Addressed High-Priority ITPA Issues
b-scan at fixed q, BT
- b-dependence important to ITER
advanced scenarios (Bt98y2~b-0.9)
- Factor of variation in bT
- Degradation of tE with b weak on NSTX
ne*-scan at fixed q
- Factor of >3 variation in ne*
- Strong increase of confinement with
decreasing collisionality
20% variation in re, ne*
k=2.1
d=0.6
SMK – 21st IAEA 4

5. 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
SMK – 21st IAEA 5

6. Dedicated H-mode Confinement Scaling Experiments Have Revealed Some Surprises
Strong dependence of tE on BT
Weaker dependence on Ip
H98y,2 ~ → → 1.4
H98y,2 ~ → → 1.1
4 MW
4 MW
tE,98y,2 ~ BT0.15
tE,98y,2 ~ Ip0.93
NSTX tE exhibits strong scaling at fixed q
tE~Ip at fixed q tE,98y,2~Ip1.1 at fixed q
SMK – 21st IAEA 6

7. Variation of Electron Transport Primarily Responsible for BT Scaling
Broadening of Te & reduction in ce outside r/a=0.5 with increasing BT
Ions near neoclassical
Neoclassical
SMK – 21st IAEA 7

8. Theory/Gyrokinetic Calculations Suggest ETG May Play an Important Role in Determining Electron Transport at Low BT
ETG linearly unstable only at lowest BT
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
SMK – 21st IAEA 8

9. Ion Transport Primarily Governs Ip Scaling - Ions Near Neoclassical Level -
GTC-Neo neoclassical:
includes finite
banana width
effects (non-local)
ci,GTC-NEO
(r/a= )
SMK – 21st IAEA 9

10. Turbulence Measurements + Gyrokinetic Calculations Have Helped Identify Possible Sources of Transport
Microwave scattering system measures
reduced fluctuations (n/n) in both upper
ITG/TEM and ETG ranges during H-mode ~
Ion and electron transport change
going from L- to H-modes
ELMs
Electron transport
reduced, but remains
anomalous
Ion transport during
H-phase is
neoclassical
- Localized measurement (axis to edge)
- Excellent radial resolution (6 cm)
SMK – 21st IAEA 10

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
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])
SMK – 21st IAEA 11

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 bT scalings
No degradation of BtE with bT
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 12

13. Backup Vugraphs
SMK – 21st IAEA 13

14. New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes
51-point CHERS
20-point MPTS
12 channel MSE [NOVA Photonics]
LRDFIT
Reconstruction
Rmag
Important for equilibrium and
microinstability calculations
Tangential microwave scattering measures
localized electron-scale turbulence
kr=2 (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)
SMK – 21st IAEA 14

15. New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes
Tangential micorwave scattering measures
localized electron-scale turbulence
12 channel MSE [NOVA Photonics]
kr=2 (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)
LRDFIT
Reconstruction
Important for equilibrium and
microinstability calculations
SMK – 21st IAEA 15

16. Dimensionless Variable Scans Have Addressed High Priority ITPA Physics Issues (e, b - scaling)
ITER98PB(y,2) scaling does
not represent low R/a data well
b-scan at fixed re, ne*
- b-dependence important to ITER
advanced scenarios (Bt98y2~b-0.9)
- Degradation of tE with b weak on NSTX
20% variation in re, ne*
NSTX data used in conjunction with ITPA data to establish e (=a/R) scaling with more confidence
t98y2~Ip0.93BT0.15ne0.41P-0.69R1.97e0.58…
tnew~Ip0.73BT0.36ne0.39P-0.62R2.14e1.03
(Kaye et al., PPCF 48 [2006] A429)
2-2.5 variation in bT
SMK – 21st IAEA 16

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 17

18. Pellet Perturbations Are Being Used to Probe Relation of Critical Gradient Physics to q-Profile
Soft X-ray array
diagnoses fast DTe
R/LTe
t=440→444 ms
H-mode with monotonic q-profile exhibits stiff profile behavior
→ Te close to marginal
stability
R/LTe
t=297→301 ms
Reversed magnetic shear L-mode responds to pellet perturbation
over several ms
Stutman, JHU
SMK – 21st IAEA 18