An overview of electron thermal transport results from NSTX

1
An overview of electron thermal transport results
from NSTX
Columbia U Comp-X General Atomics INEL Johns
Hopkins U LANL LLNL Lodestar MIT Nova
Photonics NYU ORNL PPPL PSI SNL UC Davis UC
Irvine UCLA UCSD U Maryland U New Mexico U
Rochester U Washington U Wisconsin Culham Sci
Ctr Hiroshima U HIST Kyushu Tokai U Niigata
U Tsukuba U U Tokyo Ioffe Inst TRINITI KBSI KAIST
ENEA, Frascati CEA, Cadarache IPP, Jülich IPP,
Garching U Quebec
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
2
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

3
High ne, bt H-mode Ti, Te,and calculated heating
profiles reveal dominance of electron thermal
conduction
7 MW H-Mode (bt 25, tE tE,98y2)
T (keV)
Vf(km/s)
ne (1013 cm-3)
8

Ti
6
1.2
Te
4
q
2
0.8
40
80
120
160
R (cm)
Vf
0.4
electron heating
R0
1
ion heating
w/cm-3
40
80
120
160
R (cm)
0
0
0.5
1
r/a

• Ti gt Te although beams predominantly heat
  electrons
• No strong core MHD activity observed. Type-I ELMs
  at 50 Hz

4
Power balance reveals rapid electron thermal
transport with ions near neoclassical predictions
7 MW NB H-Mode
112596a04
(similar plasma as 112596)

• For r/a lt 0.4 very small gradients, large
  calculated heat deposition gt large ? values.
  Also, only weak candidate instabilities
  identified in this region.

5
Two candidates for driving electron thermal flux
in STs emerge in nonlinear GS2 calculations
ES

• 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 gt 10 m2/s
• - to be carried out for NSTX

m2/s
?e
EM
6
Electron transport can be reduced in NSTX
Ip (MA)
1.0
Fast ramp
Slow ramp
0.5
2 MW NB

• 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, Vf1 Vf2)

ltnegt (cm-3)
2 1013
1 1013
2.0
Te0 (keV)
1.0
Vf0 (Km/s)
200
100
t1
t2
0.1
0.2
0.3
0.4
0.0
t (s)
7
Steep Te,Ti gradients develop in fast ramp case
T (keV)
Te
1.5

Fast Ramp (t1)
Ti
1.0
wf (105 s-1)
ne (1013 cm-3)
0.5
2.0
2.0
R0
1.0
1.0
1.5

Slow Ramp (t2)
Te
Ti
1.0
0
0.5
1
0
0.5
1
r/a
r/a
0.5
R0
40
80
120

160
R (cm)

• Comparable wf, Ti/Te, collisionality and b (8)

8
In L mode, transport varies with magnetic shear
Fast ramp
Slow ramp
4
4
TRANSP q(r)
TRANSP q(r)
2
2
USXR q2
0.4
0.2
0.6
0.8
0.4
0.2
0.6
0.8
c (m2/s)
c (m2/s)
100
100


ce
ci
10
10
ce
1
1
ci
ciNC
ciNC
TRANSP q(r)
4
0.4
0.2
0.6
0.8
0.4
0.2
0.6
0.8
r/a
r/a
9
Electron and ion barriers are at different radii
T (keV)

1.5
Fast ramp (t0.21 s)
Ti
Te
1.0
0.5
R0
R (cm)
40
80
120
160
0.4
0.4
max(slt0)
qmin
0.3
0.3
t (s)
eITB
t (s)
0.2
0.2
iITB
0.1
0.1

0.2
0.4
0.2
0.4
r/a
r/a

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

10
Reduced instability drive in regions of s lt 0
Fast ramp
Slow ramp
106
106
wExB
g,wExB (s-1)
wExB
3
3
q
q
105
105
2
2
104
104
0.4
0.2
0.6
0.8
0.4
0.2
0.6
0.8
r/a
r/a
ITG-TEM
Redi
µ-tearing (kqri lt1)
ETG

• 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 lt 0, s
  0

11
A first comparison to paleoclassical theory
undershoots H mode, but intriguing similarity in
trends in the L mode core
L mode, slow and fast Ip ramp
PC theory
slow ramp
fast ramp
slow ramp
fast ramp
Power balance
0.8
0.4
0.2
0.6
r/a

• 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

12
Type-I ELM impact large on core Te, smaller on ne
Te
112581 (7 MW NBI, 1 MA, 4.5 kG)
USXR
Ha
From MPTS (LeBlanc)
ne

• Thomson Te profile drops after ELM and recovers
  17 ms later
• Note ?Te does not change at drop
• Density profile little perturbed

13
Te(r,t) from SXR shows rapid arrival of edge
perturbation in core
112550
MPTS t1
MPTS t2
ELM
Te
keV

• Fast time response inferred from "two color"
  USXR spectroscopy (Stutman, Tritz, JHU)
• Te profile evolves with little change in
  gradient (resiliency)

r0.2
r0.4
r0.6
r0.8
Selectable cutoff energies - core/edge MHD
imaging - two-color Te profiles
t (ms)
R/LTe from t480 to t484 ms
R (cm)
14
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

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Two regions with different transport
characteristics are suggested by cold pulse
propagation
Time-to-peak (ms)
Te at t1 (keV)
2.0
1.5

• cet peak 1/8 Dr2/Dtpeak (sawtooth model)
• -gt hundreds m2/s outside r gt 0.5
• -gt tens of m2/s inside
• Opposite trend to cePB
• Suggests electron transport strongly driven
  above critical in the ?Te region and nearer to
  threshold where Te flattens

1.0
0.5
r
1000
cet peak
cePB
ce (m2/s)
100
10
r
17
NSTX electron thermal transport plan takes
advantage of some unique plasma characteristics

• Anisotropic turbulence strong toroidal
  curvature Bragg condition
• ? Excellent spatial resolution
• ??--gt 1 locally, low B
• ? Big modes, emergent e-m effects
• ? Unique opportunity to study electron scale
  turbulence

Localized scattering volume
k 20 cm-1
k 10 cm-1
4 cm fwhm
13 cm fwhm
Instrument selectivity, from ray tracing
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Linear GS2 calculations predict instabilities in
the gradient region, but not on the region with
smaller gradients
g, wExB (x106 s-1)
7 MW H-Mode
1.0
Te
ITG-TEM
wExB
Redi, Core WG II, Th. AM
µ-tearing (kqri 1-4)
0.5
ETG
0.2
0.4
0.6
0.8
r/a

• Is it the weak shear in the core?