# Presentation: 536543

## Confinement, Transport and Turbulence Properties of NSTX Plasmas

**Confinement, Transport and Turbulence Properties of NSTX Plasmas**

- _S.M. Kaye__*_, R.E. Bell, B.P. LeBlanc,
- D. Mikkelsen, H. Park, G. Rewoldt,
- W. Wang (PPPL),
- D. Stutman, K. Tritz (JHU),
- F. Levinton, H. Yuh (Nova Photonics)
- *PPPL, Princeton University, Princeton, NJ
**EPS Meeting**
- July 2-6, 2007
- Warsaw, Poland

***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***
***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***
***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 Poster Will Focus on Confinement & Transport Trends in NSTX and Their Underlying Processes

- Key confinement and transport dependences established (BT, Ip, , , q(r),...)
- Dedicated scans have isolated Ip and BT dependences
- Theory/simulations have indicated ETG and microtearing modes could be important in controlling electron transport
- Localized turbulence characteristics being assessed across wide range of k (upper ITG/TEM to ETG)
- Dimensionless parameter scans in T
- Studied effect of plasma shaping on -degradation of confinement
- Momentum transport studies just beginning
- Momentum and ion transport decoupled in NSTX

## 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)

## 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 (3 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*

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

## 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

## Local Transport Studies Reveal Sources of Energy Confinement Trends

***Local Transport Studies Reveal Sources of Energy Confinement Trends***

- Electrons primarily responsible for
- strong BT scaling in NSTX (E~BT0.9)

- Electrons anomalous

- Ions near neoclassical

- Variation in near-neoclassical ion
- transport primarily responsible
- for _I__p_ scaling (E~Ip0.4)

- Neoclassical

- Neoclassical levels determined from GTC-Neo:
- includes finite banana width effects (non-local)

## 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

- 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

- TRANSP

- Saturated
- ETG level

- Qe (kW/m2)

## Change in High-k Scattering Spectra with r/a and BT Consistent with Variations of e

- Core measurement shows increase of fluctuations at higher BT (consistent with higher e at higher BT)

- Outboard edge measurement shows decrease of fluctuations at higher BT (consistent with lower e at higher BT)

- [see Park et al., P2.045]

## Strongly Reversed Magnetic Shear L-mode Plasmas Achieve Higher Te and Reduced Transport

- Linear GS2 calculations indicate reduced region of tearing instability for RS plasma (r/a=0.3)
-    ETG stable in this
-    region in both
-    plasmas
- (see Wong, this conf)

- F. Levinton, APS 2006

- Calculated high-k-driven turbulent transport heat fluxes outside RS region consistent with inferred level

- (D. Mikkelsen)

## Dimensionless Parameter Scans Have Addressed High-Priority ITPA Issues – Beta Dependence of Confinement

***Dimensionless Parameter Scans Have Addressed ******High-Priority ITPA Issues – Beta Dependence of Confinement***

- -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

## Power/Beta Scan Was Repeated at Lower  to Test Effect of Shape on Confinement Dependence

-  =1.8-1.9, ~0.4; e, e vary ≤ 20% across scan
-  ELM severity increased with increasing power

- Weak increase of  with power
- Type III ELMs severely degrade confinement

## Confinement Exhibits Strong Degradation with T in Weakly-Shaped Plasmas

- Stronger degradation of E,th than T,th-0.35 cannot be ruled out

- Strong degradation of E (E ~ T-1.0)

## Momentum Confinement Studies

- Low BT (0.35-0.55 T) operation leads to values of ExB up to the MHz range
- These ExB shear values can exceed ITG/TEM growth rates by factors of 5 to 10
- Statistical studies indicate  does not scale with i in NSTX

- Due to suppression of ITG modes?

## Steady-State Momentum Transport Determined From BT, Ip Scans

***No anomalous pinch necessary to explain steady-state rotation data***

## Core Momentum Diffusivities Up to An Order of Magnitude Lower Than Thermal Diffusivities

- Does  scale with e?
- What is ,neo?
-       (0.1-0.4 m2/s by very simple estimate)

## Dedicated Perturbative Momentum Confinement Experiments Recently Carried Out

- Use non-resonant n=3 magnetic perturbations to damp plasma rotation; turn nRMP off for plasma spin-up
- Use plasma spin-up dynamics to determine , vpinch

## Instantaneous and Perturbative Determination of  During Spin-up Agree

- Use dL/dt = T – L/ relation to determine instantaneous 
- Model spin-up to determine perturbative  using
- 	L(t) =  * [T – (T-L0/) * exp(-t/)], where
- 			L = Angular momentum
- 			T = Torque
- 			L0 = Angular momentum at time of nRMP turn-off

## Detailed Energy and Momentum Confinement Studies in NSTX Are Underway

- 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**?)*
- Theory indicates that high-k ETG modes could be important
- Need also to consider lower-k modes in some cases (ITG/TEM)
- No degradation of BE with T in strongly-shaped plasmas
- Degradation seen in more weakly-shaped plasmas
- Degradation invariably tied to change in ELM severity
- Momentum transport studies are just beginning
- Steady-state power balance and perturbative analyses indicate long momentum confinement times (>100 ms), with <<i
- Momentum diffusivity does not scale with ion thermal diffusivity
- Possibly due to suppression of ITG modes in NSTX, and neoclassical transport controlling both ion heat and momentum diffusion