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

1
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, xxxxx 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 unique view into plasma TT
  properties
• NSTX operates in a unique 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

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 up to 40
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, Er, q(r),..)
• Data contributed to ITPA database to address high
  priority ITPA tasks
• Localized turbulence characteristics being
  assessed across wide range of k (ITG/TEM to ETG)
• Theory/simulations have indicated potential
  importance of ETG in controlling electron
  transport
• New diagnostic capabilities since last IAEA have
  facilitated progress in our understanding of
  transport processes

Tangential scattering measures localized
electron-scale turbulence
12 channel MSE NOVA Photonics

• kr2 (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 microinstability calc
ulations
LRDFIT Reconstruction
4
Dedicated H-mode Confinement Scaling Experiments
Have Been Carried Out To Study Confinement
Transport Trends
Scans carried out at constant density,
injected power (4 MW)
5
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
6
Dimensionless Variable Scans Have Addressed
HighPriority ITPA Physics Issues (b, e - 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
7
Local Transport Studies Reveal Sources of
Confinement Trends
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
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 - R/LTe
just above critical gradient (20)
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

9
Ion Transport Primarily Governs Ip Scaling- Ions
Near Neoclassical Level -
GTC-Neo neoclassical includes finite banana
width effects (non-local)
10
Increased Magnetic Shear Is Associated with
Reduced Transport
Weak vs Reverse-Shear L-mode
Global non-linear GTC simulations show that a
pure ITG mode is unstable in both cases, but it
drives little transport
ExB flows not included TEM ETG calculations un
derway
11
Pellet Perturbations Are Being Used to Probe
Local Transport Properties and Critical Gradient
Physics
Soft X-ray array diagnoses fast Te changes in
response to Li pellet injection
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
Te in reversed magnetic shear L-mode responds to
pellet perturbation over several ms
Stutman, JHU
12
Turbulence Measurements Gyrokinetic
Calculations Have Helped Identify Possible
Sources of Transport
Ion and electron transport change going from L-
to H-modes
Ion transport during H-phase at neoclassical level
Electron transport reduced, but remains anomalous
13
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-phase ETG
unstable
glin gtgt gExB during L-phase for all kqrs glin ltlt
gExB during H-phase for ITG/TEM glin gExB
during H-phase for ETG
121283
Non-linear GTC results indicate ITG modes stable
during H-phase
Experimental ce profile consistent with that
predicted by e-s ETG theory (Horton et al, Phys.
Plasmas 2004)
14
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 no degradation of
  BtE with bT
• Data provided to ITPA H-mode database for R/a and
  bT scalings
• Understand the source of the difference in
  confinement trends at different R/a
• Electron transport variation primarily
  responsible for BT scaling
• Ions near neoclassical primarily responsible for
  Ip scaling
• Transport in electrons and ions can be reduced
  with control of q(r)

• Localized turbulence levels decrease going from
  L- to H-mode across kr range from 2 to 24 cm-1
  (upper ITG/TEM to ETG range)
• Associated with reduction in transport
• Analytic theory and gyrokinetic calculations
  (linear and non-linear) have indicated the
  potential importance of ETG modes under some
  circumstances
• Need also to consider lower-k modes
• (microtearing, ITG/TEM)