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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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.
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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)
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
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
Synakowski, TTF Napa 2005
Synakowski, TTF Napa 2005
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
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