An overview of electron thermal transport results from NSTX

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E.J. Synakowski, M. Redi, D. Stutman1, K. Tritz1, M.G. Bell, R.E. Bell, W. Dorland2, M. Finkenthal1, K.W. Hill, S.M. Kaye, B.P. LeBlanc, N. Luhmann3, J.E. Menard, H. Park, S. Sabbagh4, D. Smith

Princeton Plasma Physics Laboratory[1] Johns Hopkins University[2] University of Maryland, College Park[3] U.C. Davis[4] Columbia University

TTF 2005, Napa, California

An overview of electron thermal transport results from NSTX

Synakowski, TTF Napa 2005

Electron thermal transport is emerging as a major focus for NSTX transport research

• Background – The electron channel typically dominates thermal conduction on

NSTX in H and L mode e can be changed via current profile changes

• New capabilities– ∆Te measurement capability reveals rapid responses to edge

perturbations

• Theory chimes in– GS2, paleoclassical


High ne, t H-mode: Ti, Te,and calculated heating profiles reveal dominance of electron thermal conduction

• Ti > Te although beams predominantly heat electrons

• No strong core MHD activity observed. Type-I ELMs at ≈ 50 Hz

7 MW H-Mode (t ≈ 25%,≈ y

R (cm)

2468

ne (1013 cm-3)

40 80 120 160

0.4

0.8

1.2

R0

Te Ti

40 80 120 160R (cm)

T (keV)

V

V(km/s)

50

100

150

200

250

electron heating1

00 0.5 1

r/a

ion heating

q

w/cm-3


Power balance reveals rapid electron thermal transport with ions near neoclassical predictions

7 MW NB H-Mode

e

iNC

i

(m2/s)

1

10

100

0.40.2 0.6 0.8r/a

20 msvariability

112596a04

(similar plasma as 112596)

For r/a < 0.4: very small gradients, large calculated heat deposition ==> large values. Also, only weak candidate instabilities identified in this region.


Two candidates for driving electron thermal flux in STs emerge in nonlinear GS2 calculations

• ETG simulation yields e ~ 10 m2/s (1/2 radius: gradient region)

- dominantly electrostatic

• tearing also yields high fluxes. Simulations from MAST (not shown) indicate EM heat flux over ES, e > 10 m2/s

- to be carried out for NSTX

ES

EM

e m2/s


Electron transport can be reduced in NSTX

• Investigate magnetic shear

effects in low ne, high Te L-Modes

• Vary Ip ramp rate, beam onset

time to vary magnetic shear

• Times t1 and t2 for comparison of

magnetic shear effects (no

reconnections, ne1 ≈ ne2, V1≈ V2)

Fast ramp Slow ramp

1.0

0.5

Ip (MA)

2 1013 <ne> (cm-3)

1 1013

2.0

1.0

Te (keV)

0.1 0.2 0.3 0.40.0t (s)

V (Km/s)200

100t1 t2

2 MW NB


Steep Te,Ti gradients develop in fast ramp case

• Comparable , Ti/Te, collisionality and ≈8%)

T (keV)

1.0

2.02.0

1.0

ne (1013 cm-3) (105 s-1)

r/a0.5

1.0

1.5

R0

Te Ti

40 80 120 R (cm)

R0

Te Ti

0.5

1.0

1.5Fast Ramp(t1)

Slow Ramp(t2)

0 0.5 1 0 0.5 1r/a

160


In L mode, transport varies with magnetic shear

Fast ramp Slow ramp

0.40.2 0.6 0.8

2

4TRANSP q(r)

2

4

0.40.2 0.6 0.8

TRANSP q(r)

r/a r/a

4TRANSP q(r)

e

iNCi

1

10

100

e

iNC

i

1

10

100

0.40.2 0.6 0.8 0.40.2 0.6 0.8

(m2/s) (m2/s)

USXR q=2


Electron and ion barriers are at different radii

• Electron ITB in region of large negative shear

• Ion ITB in region of low magnetic shear (near qmin)

T (keV)

Fast ramp(t≈0.21 s)

R (cm)

0.5

1.0

1.5

R0

Te Ti

40 80 120 160

qmin

r/a

0.4

0.3

0.2

0.1 0.2 0.4

t (s)iITB

t (s)

r/a

0.4

0.3

0.2

0.1 0.2 0.4

max(s<0)eITB


Reduced instability drive in regions of s < 0

Redi ITG-TEMµ-tearing (ki <1)

ETG

106

105

104

r/a0.40.2 0.6 0.8

106

105

104

r/a0.40.2 0.6 0.8

q 3

2

q3

2

• ITG-TEM reduced in iITB region (s ≈ - 0.6)• µ-tearing reduced in eITB region (s ≈ -1.7) - preliminary

• ETG reduced or stable in regions of s < 0, s ≈ 0

Fast ramp Slow ramp

ExB,ExB

s-1)

ExB


A first comparison to paleoclassical theory: undershoots H mode, but intriguing similarity in trends in the L mode core

• Collisionless limit of PC theory, no consideration of simple rational q values

• In theory, 1/|q'|0.5 dependence plays a large role in the e drop

e

1

10

100

0.40.2 0.6 0.8r/a

ePC

H mode

m2/s

0.40.2 0.6 0.8r/a

1

10

100

Power balance

L mode, slow and fast Ip ramp

slow ramp

PC theory

fast ramp

slow ramp

fast ramp

From Callen, PRL & UW-CPTC 04-3


Type-I ELM impact large on core Te, smaller on ne

USXR

H

• Thomson Te profile drops after ELM

and recovers ~ 17 ms later

• Note Te does not change at drop

• Density profile little perturbed

#112581 (7 MW NBI, 1 MA, 4.5 kG) Te

ne

From MPTS (LeBlanc)

Synakowski, TTF Napa 2005R (cm)

keV MPTS t2

USXR

R/LTe from t=480 to t=484 ms

R (cm)

=0.8

=0.6

=0.4

=0.2

MPTS t1 MPTS t2ELM

#112550

TekeV

• Fast time response inferred from "two color"

USXR spectroscopy (Stutman, Tritz, JHU)

• Te profile evolves with little change in gradient

(‘resiliency’)

Te(r,t) from SXR shows rapid arrival of edge perturbation in core

Selectable cutoff energies: - core/edge MHD imaging - ‘two-color’ Te profiles

475 480 490 495485t (ms)


Electron thermal transport is emerging as a major NSTX research focus

• Electron thermal transport typically dominates thermal conduction on NSTX in H and L mode

e can be changed via the current profile

• ∆Te measurement capability reveals rapid responses to edge perturbations

• Linear analysis predicts a wide variety of modes. Nonlinear analysis indicates ETG transport can account for fluxes in outer region of H mode.

• First cut at paleoclassical - misses on the H mode, captures some aspects of core changes in the L mode cases

• High k measurement plans for 2005: unique opportunities


Time-to-peak (ms) Te at t1 (keV)

0.5

1.0

1.5

2.0

Two regions with different transport characteristics are suggested by cold pulse propagation

e

(m2/s)

10

100

1000

• et peak = 1/8 r2/tpeak (sawtooth model)

-> hundreds m2/s outside > 0.5

-> tens of m2/s inside

• Opposite trend to ePB

• Suggests electron transport strongly driven

above critical in the Te region and nearer to

threshold where Te flattens

et peak

ePB


NSTX electron thermal transport plan takes advantage of some unique plasma characteristics

• Anisotropic turbulence + strong toroidal curvature + Bragg condition

Excellent spatial resolution

--> 1 locally, low B

Big modes, emergent e-m effects

Unique opportunity to study electron scale turbulence

k = 10 cm-1 k = 20 cm-1

4 cm fwhm

13 cm fwhm

Instrument selectivity, from ray tracing

Localized scattering volume

ETG

0.1 1 10 100

ITG ITG/TEM

tearing

k (cm-1)

k s

0.1 1 10

High k scattering

range



Linear GS2 calculations predict instabilities in the gradient region, but not on the region with smaller

gradients

• Is it the weak shear in the core?

, ExB (x106 s-1)

7 MW H-Mode

Redi, Core WG II, Th. AM

Te

ExB

0.2 0.4 0.6 0.8

1.0

0.5

r/a

ITG-TEM

µ-tearing (ki ≈ 1-4)

ETG

Documents

An overview of electron thermal transport results from NSTX