# Presentation: 683883

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

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

_**Stanley M. Kaye**__**1**_, 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
**21****st**** 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, J******ü******lich***
***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

***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***

## 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 m
- Aspect Ratio A		1.3
- Elongation 		2.8
- Triangularity 		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
- T,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)

## 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 Te
- Established more accurate   (=a/R) scaling with NSTX (& MAST) data included in the ITPA database
- 		98y2~Ip0.93 BT0.15 ne0.41 P-0.69 R1.97 ******0.58**...
- new~Ip0.73 BT0.36 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

## Dimensionless Parameter Scans Have Addressed High-Priority ITPA Issues

*Dimensionless Parameter Scans Have Addressed **High-Priority ITPA Issues*

- -scan at fixed q, BT
-   - -dependence important to ITER
-     advanced scenarios (B98y2~-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

## 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

## Dedicated H-mode Confinement Scaling ExperimentsHave Revealed Some Surprises

*Dedicated H-mode Confinement Scaling Experiments**Have Revealed Some Surprises*

-      ***Strong dependence of ************E****** on B******T***

- 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 I******p***

- E~Ip1.3-1.5 at fixed q                  E,98y,2~Ip1.1 at fixed q

- NSTX E exhibits strong scaling at fixed q

- 4 MW

## Variation of Electron Transport Primarily Responsible for BT Scaling

*Variation of Electron Transport Primarily **Responsible for B**T** Scaling*

- Broadening of Te & reduction in e outside r/a=0.5 with increasing BT

- Ions near neoclassical

- Neoclassical

## Theory/Gyrokinetic Calculations Suggest ETG May Play an Important Role in Determining Electron Transport at Low BT

*Theory/Gyrokinetic Calculations Suggest ETG May Play an **Important Role in Determining Electron Transport at Low B**T*

- Non-linear simulations indicate formation of radial streamers (up to 200e): 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

## Ion Transport Primarily Governs Ip Scaling- Ions Near Neoclassical Level -

*Ion Transport Primarily Governs I**p** Scaling**- Ions Near Neoclassical Level -*

- i,GTC-NEO
-     (r/a=0.5-0.8)

- _GTC-Neo_ neoclassical:
- includes finite
- banana width
- effects (non-local)

## Turbulence Measurements + Gyrokinetic Calculations Have Helped Identify Possible Sources of Transport

*Turbulence Measurements + Gyrokinetic Calculations Have Helped Identify Possible Sources of Transport*

- Ion transport during
- H-phase is
- neoclassical

- Electron transport
- reduced, but remains
- anomalous

- Ion and electron transport change
- going from L- to H-modes

- - Localized measurement (axis to edge)
- - Excellent radial resolution (6 cm)

## Theory/Gyrokinetic Calculations Indicate Both ITG/TEM and ETG are Possible Candidates for Electron Transport

*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 consistent
- with that predicted by e-s ETG theory
- (Horton et al, Phys. Plasmas [2004])

- Non-linear GTC results
- indicate ITG modes
- stable during H-phase;
- i  ~ neoclassical

## NSTX Plays a Key Role in Multi-Scale Transport & Turbulence Research

*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, B**T**?)*
- Data provided to ITPA H-mode database for R/a and T scalings
- No degradation of BE with T

## Backup Vugraphs

## New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes

*New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes*

- 12 channel MSE [NOVA Photonics]

- LRDFIT
- Reconstruction

- Rmag

- 51-point CHERS

- 20-point MPTS

- Tangential microwave scattering measures
- localized 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

## New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes

- Tangential micorwave scattering measures
- localized electron-scale turbulence

- 12 channel MSE [NOVA Photonics]

- 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)

## Dimensionless Variable Scans Have Addressed HighPriority ITPA Physics Issues (- scaling)

*Dimensionless Variable Scans Have Addressed High**Priority ITPA Physics Issues (****- scaling)*

- -scan at fixed e, e*
-   - -dependence important to ITER
-     advanced scenarios (B98y2~-0.9)
-   - Degradation of E with  weak on NSTX

- 	NSTX data used in conjunction with ITPA data to establish ****(=a/Rscaling with more confidence

- ITER98PB(y,2) scaling does
- not represent low R/a data well

- 98y2~Ip0.93BT0.15ne0.41P-0.69R1.97******0.58**...
- new~Ip0.73BT0.36ne0.39P-0.62R2.14******1.03**
-     (Kaye et al., PPCF **48** [2006] A429)

- 2-2.5 variation in T

- 20% variation in e, e*

## Stronger Reversed Magnetic Shear Is Associated with Reduced Transport

*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

## 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 perturbation
- over several ms

- Soft X-ray array
- diagnoses fast Te

- R/LTe
- t=297→301 ms

- R/LTe
- t=440→444 ms

- Stutman, JHU