Transcript Physics Results From the National Spherical Torus Experiment (NSTX)

Supported by
Office of
Science
Physics Results From the National Spherical
Torus Experiment (NSTX)
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
SMK – LLNL
Stanley M. Kaye for the NSTX Group
PPPL, Princeton University, Princeton, NJ
UCLA Colloquium
March 8, 2007
Los Angeles, Cal.
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, Jülich
IPP, Garching
ASCR, Czech Rep
U Quebec
1
A Spherical Torus is a Low Aspect Ratio
Tokamak
R/a~4, k=2, qa=4
R/a~1.3, k=2, qa=12
New physics regimes are expected at low aspect ratio
SMK – LLNL
• Intrinsic cross-section shaping (k>2, BT/Bp ~ 1)
- Enhanced stability (higher b)
- High bootstrap current fraction (>50% of total)
• Strong toroidicity – field line length in good curvature region maximized
- Benefits stability and confinement
• Large fraction of trapped particles
• Large gyroradius (a/ri ~ 30 – 50)
• Large plasma flow and flow shear (M ~ 0.5)
• Supra-Alfvénic fast ions (vbeam/VAlfvén ~ 4)
2
NSTX Addresses Key Issues for Plasma Science,
ITER Physics and Fusion Energy Development
• Determine the physics principles of
Spherical Torus (ST) confinement
• Complement and extend
conventional aspect ratio tokamaks
• Support preparation of burning
plasma research in ITER
– Participate in the ITPA and USBPO
• Complement ITER by exploring
attractive configurations for a
Component Test Facility (CTF) and
Demonstration Power Plant
SMK – LLNL
Major Radius R0
Aspect Ratio A
Elongation k
Triangularity d
Plasma Current Ip
Toroidal Field BT
Pulse Length
NB Heating (100 keV)
bT,tot
0.85 m
1.3
2.8
0.8
1.5 MA
0.55 T
1.5 s
7 MW
up to 40%
3
What are the Key ST Physics Issues to Address?
Issue
SMK – LLNL
Motivation
High-b stability
Sustain high plasma
pressure (beta) at low
magnetic field
Electron confinement
Ion transport near
neoclassical
NSTX Research
Passive plates,
Error field correction,
Active RWM control
Measure and understand
electron-scale turbulence,
Roles of q, Er shear in
microinstability control
Fast particle stability and
confinement
vb/vA>1 → *AE modes;
also low-n, multi-modes
Establish stability
boundaries,
Develop phase space
control
High divertor heat fluxes
Compact divertor (P/R
approaches ITER level)
Radiative divertor,
Lithium coatings and PFC
Non-inductive operation
No room for conventional
solenoid in compact
reactor
CHI for startup,
RFCD for ramp-up,
NBCD+BS for
sustainment
4
NSTX Plasmas Approach the Normalized Performance Needed for a
Spherical Torus - Component Test Facility (ST-CTF)
Design optimization for a moderate Q driven ST-CTF:
• Minimize BT required for desired wall loading  Maximize <p>/BT2 = bT
• Minimize inductive current  Maximize fbs  0.5bP
• Do this simultaneously  Maximize fbsbT  0.5bPbT
bT = 15 – 25%
fBS = 45 – 50%
SMK – LLNL
fbs = 0.30.5bpol
Goal of a driven ST-CTF:
DT neutron flux = 1 – 4 MW/m2
Achievable with:
A = 1.5, k = 3,
R0 = 1.2 m, IP = 8 – 12 MA
bN ~ 5 %-m-T/MA, H98y,2 = 1.3
Approximate Bootstrap Fraction
WL= 1 MW/m2 4 MW/m2
5
Optimized Plasma Shape/Boundary Can Lead to
Higher bpol and fBS Operation at High bT
• High k is a route to increasing bootstrap current
• Sustained k2.8 for many twall using rtEFIT isoflux control
Divertor coil upgrade
2004
2005
k = 3.0, dX = 0.8
li = 0.45
Vertically
unstable
k
Gates, et al., PoP 13 (2006) 056122
Gates, et al., NF 46 (2006) 17
SMK – LLNL
fNI=100%
target
Vertically stable
operating space
li
6
High Performance Can Be Sustained For Several Current
Redistribution Times at High Non-Inductive Current Fraction
• p and NBI current drive provide up to 65% of plasma current 
- High bN  H89P now sustained for up to ~5 current relaxation times
TRANSP non-inductive current fractions
1
Ip (MA)
PNBI (MW)/10
1.0
0
Ohmic
Current fraction
p
NB-driven
0.5
Bootstrap
(NCLASS)
116318A13
0.0
SMK – LLNL
0.5
1.0
Time (s)
1.5
0.0
D. Gates, PoP 13, 056122 (2006)
7
Outline
•
•
•
•
•
•
SMK – LLNL
Macroscopic Stability
Transport and Turbulence
Energetic Particle Physics
Boundary Physics
Plasma Startup and Rampup
Integrated High Performance
8
NSTX Extends the Stability Database Significantly
bT = 2µ0<p>/BT02 (%)
• A = 1.5
• k = 2.3
• dav = 0.6
• q95 = 4.0
• li = 0.6
• bN = 5.9%·m·T/MA
• bT = 40% (EFIT)
34% (TRANSP)
Normalized current Ip/a·BT (MA/m·T)
• Seeing benefits of
– Low aspect ratio
– Cross-section shaping
– Stabilization of external modes by conducting plates
SMK – LLNL
9
Both Internal and External Modes Can be
b-Limiting in NSTX
Discharge (in black) collapses as
rotation flattens and decreases
bT (%)
bT  31%
Non-linear M3D
results consistent
with experiment
Resistive Wall Modes can
limit bT at low-q
(Sabbagh et al., NF, 44 [2004] 560)
bT  23%
ff(0) (kHz)
Mode Bq (Gauss)
q0
(w/o
MSE)
SMK – LLNL
Maintaining high rotation is a key to stabilizing both modes
10
External Control Coils Used to Actively Compensate
Error Fields and Resistive Wall Modes
6 External
Control Coils
48 Internal
BP, BR sensors
Copper
stabilizing plates
SMK – LLNL
11
Resistive Wall Mode (RWM) Actively Stabilized at
Low, ITER-Relevant Rotation
Sabbagh et al., PRL 97 (3006) 04500
SMK – LLNL
•
Plasma rotation reduced by
non-resonant n=3 magnetic
braking
•
RWM becomes unstable
when rotation drops below a
critical value
•
Data from internal sensors
detects mode in real-time
•
Feedback system applies
correcting n=1 field
perturbation with
appropriate amplitude and
phase
- Optimize RWM control
- Fully understand stabilization
physics
12
Outline
•
•
•
•
•
•
SMK – LLNL
Macroscopic Stability
Transport and Turbulence
Energetic Particle Physics
Boundary Physics
Plasma Startup and Rampup
Integrated High Performance
13
NSTX offers a novel view into plasma T&T properties
• NSTX operates in a unique part of
dimensionless parameter space
– R/a, bT, (r*, n*)
– Large range of bT spanning e-s to e-m
turbulence regimes
• Dominant electron heating with NBI
– Relevant to a-heating in ITER
• Excellent laboratory in which to study
electron transport
– Electron transport anomalous, ions
close to neoclassical
– Localized electron-scale turbulence
measurable (re ~ 0.1 mm)
• Strong rotational shear that can
influence transport
SMK – LLNL
14
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
SMK – LLNL
0.50 s
15
Results of the Scaling Experiments Have Revealed
Some Surprises
Strong dependence of tE on BT
H98y,2 ~
0.9
→ 1.1
→ 1.4
Weaker dependence on Ip
H98y,2 ~
1.4 → 1.3 → 1.1
4 MW
4 MW
tE,98y,2 ~ BT0.15
SMK – LLNL
tE,98y,2 ~ Ip0.93
16
Variation of Electron Transport Primarily
Responsible for BT Scaling
Broadening of Te & reduction in ce outside r/a=0.5 with increasing BT
Ions near neoclassical
Neoclassical
SMK – LLNL
17
Near Neoclassical Ion Transport
Primarily Governs Ip Scaling
GTC-Neo
neoclassical:
includes finite
banana width
effects (nonlocal)
ci,GTC-NEO
(r/a=0.5-0.8)
SMK – LLNL
18
Turbulence Measurements + Gyrokinetic Calculations Have
Helped Identify Possible Sources of Transport
Microwave scattering system measures
~
reduced fluctuations (n/n) in both upper
ITG/TEM and ETG ranges during H-mode
Ion and electron transport change
going from L- to H-modes
ELMs
Electron
transport
reduced, but
remains
anomalous
Ion transport
during
H-phase is
neoclassical
- Localized measurement (axis to edge)
-SMK
Excellent
radial resolution (3 cm)
– LLNL
19
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
SMK – LLNL
Non-linear GTC results indicate ITG modes stable during Hphase; ci ~ neoclassical
20
Strongly Reversed Magnetic Shear L-mode Plasmas
Achieve Higher Te and Reduced Transport
Low Density L-modes
Linear GS2
calculations indicate
reduced region of
mtearing instability for
RS plasma (r/a=0.3)
ETG stable in this
region in both
plasmas
Calculated high-kdriven turbulent
transport heat
fluxes outside RS
region consistent
with inferred level
(D. Mikkelsen)
SMK – LLNL
F. Levinton, APS 2006
Microtearing measurable by reflectometry?
21
•
•
•
•
•
•
SMK – LLNL
Macroscopic Stability
Transport and Turbulence
Energetic Particle Physics
Boundary Physics
Plasma Startup and Rampup
Integrated High Performance
22
NSTX Accesses ITER-Relevant Fast-Ion
Phase-Space Regime
• ITER will operate in new, small r* regime for fast ion transport
– k^r ≈ 1 means "short" wavelength Alfvén modes
– Fast ion transport expected from interaction of many modes
– NSTX can access multi-mode regime via high bfast / btotal and vfast / vAlfven
6
1% neutron rate decrease:
5% neutron rate decrease:
ARIES-ST
5
Vfast / VAlfvén
NSTX observes that multi-mode TAE bursts induce larger
fast-ion losses than single-mode bursts:
CTF
4
3
ITER
NSTX
2
1
0
0.0
0.2
0.4
0.6
0.8
bfast(0) / btot (0)
SMK – LLNL
E. Fredrickson, Phys. Plasmas 13, 056109 (2006)
23
Reflectometry Data Reveals 3-wave Coupling
of Distinct Fast-Ion Instabilities
EPM  Energetic Particle Mode (bounce-resonant fishbones)
TAE  Toroidal Alfven Eigenmode
• Low-f EPMs co-exist with mid-f TAE modes
Bi-coherence analysis reveals 3-wave
coupling between 1 EPM and 2 TAE modes
• Large EPM TAE phase locks to EPM
forming toroidally localized wave-packet
N. Crocker, Phys. Rev. Lett. 97, 045002 (2006)
Influence of toroidal localization of TAE mode energy on fast
ion transport and EPM/TAE stability presently being investigated
SMK – LLNL
24
Identification of b-Induced Alfvén-Acoustic
Eigenmodes (BAAE)
• EP driven modes often seen at frequencies lower than those
expected for TAE
• Couples two fundamental MHD branches (Alfvén & acoustic) – new
• Joint studies with JET
Reflectometers needed for measuring localization and mode structure
SMK – LLNL
How does this scale to ITER?
25
“Angelfish” Identified as Form of Hole-Clumps,
Consistent with Theory
•
•
•
(CAE) Mode satisfies Doppler-shifted resonance condition for TRANSP
calculated fast ion distribution (w=wc-k||vbeam)
Growth rate estimates from theory is 0.04; from observation is 0.053
Engineering of fast-ion phase space can suppress deleterious instabilities
– Angelfish suppressed with addition of HHFW
Reflectometers needed to measure mode
amplitude
Assess relation to stochastic heating threshold
SMK – LLNL
(“bump-on-tail” instability drive)
26
Alfvén Cascades (RSAE) Observed at
Low be on NSTX
TAE frequency
 vAlfven
f=(m-nq)/qR
GAM frequency
 cs
(cs/vA)2 ~ b
Also seen on MAST, JET
Implications for ITER being investigated
Frequency chirp indicates evolution of qmin
Use for q-reconstruction, MSE verification
Reflectometry needed for mode structure/localization
SMK – LLNL
27
•
•
•
•
•
•
SMK – LLNL
Macroscopic Stability
Transport and Turbulence
Energetic Particle Physics
Boundary Physics
Plasma Startup and Rampup
Integrated High Performance
28
Lithium Evaporator (LITER) Produced Particle Pumping and
Improved Energy Confinement in H-mode Plasmas
SMK – LLNL
H98y,2=1.1→1.3
R. Majeski, H. Kugel, IAEA 2006
29
Edge Imaging Has Been Key to Studying Edge
Localized Modes (ELMs)
ELM dynamics and rotation
have been measured
SMK – LLNL
30
Excellent “Blob” Measurements Have Allowed
Connection to Theory
Blob size found to be related to blob velocity
in analytic theory
J, Myra, Lodestar
Numerical modeling of blobs done using
DEGAS-2 (snapshot) and BOUT (turbulence
evolution - Umansky, LLNL)
SMK – LLNL
31
•
•
•
•
•
•
SMK – LLNL
Macroscopic Stability
Transport and Turbulence
Energetic Particle Physics
Boundary Physics
Plasma Startup and Rampup
Integrated High Performance
32
Developing Means to Initiate Solenoid-Free Plasmas and
Couple to Non-Inductive CD Methods Is Essential for ST
IP
CHI or PF-only for
plasma initiation
and early ramp-up
HHFW for ramp-up
of low Ip plasma
(bootstrap + FWCD)
200 kW
ECH/EBWH
CHI
HHFW
HHFW+NBI
time
CHI: Co-Axial Helicity Injection
ECH/EBW: 200 kW 28/15.3 GHz system planned (2009)
HHFW: 30 MHz, 6 MW, 20th harmonic
NBI: Fast ions confined for Ip>600 kA
EBW/HHFW coupling studies being carried out
SMK – LLNL
33
CHI Can Initiate Plasma Current Without Induction
• Initially developed in HIT and HIT-II devices at U. Washington
• Toroidal insulating breaks between inner, outer vacuum vessel in NSTX
• Transient CHI: Axisymmetric reconnection during decay of injected current
leads to formation of closed flux surfaces
SMK – LLNL
34
160 kA of Closed Flux Current Produced
in NSTX by Transient CHI
Evidence for high-IP flux closure:
300
250
•
IP=160kA remains after
CHI injector current ICHI  0
at t=9ms
200
Ip
kA 150
100
•
•
After t=9ms, plasma current
decays away inductively
50
0
ICHI
5
10
Time (ms)
15
Once IINJ 0, reconstructions track dynamics of detachment & decay
Current decay rate consistent with resistivity of plasma 10 – 20 eV
SMK – LLNL
R. Raman et al., PRL 97 (2006) 175002
35
•
•
•
•
•
•
SMK – LLNL
Macroscopic Stability
Transport and Turbulence
Energetic Particle Physics
Boundary Physics
Plasma Startup and Rampup
Integrated High Performance
36
NSTX Plasmas Many High-Performance Plasma
Features Simultaneously for Extended Pulse
NSTX “Hybrid”-Like Scenario as Proposed for ITER
High
Confinement
Multiplier
tCR
High Noninductive Fraction
High Normalized
Beta
Stable Boundary
SMK – LLNL
37
Integrated Modeling Points to Importance of Shaping,
Reduced ne, and Increased Te/tE for Higher fNI and High bN
• n20(0)=0.85,
k=2.2
H98=1.1
bN = 5.6
q(0) = 1.15
• n20(0)=0.36,
k=2.2
H98=1.1
bN = 5.6
q(0) = 1 @ 0.8 s
n(0)=0.75e20
SMK – LLNL
• n20(0)=0.75,
k=2.55
H98=1.35
bN = 6.6
q(0) = 1.4
38
Summary
• NSTX normalized performance approaching ST-CTF level
• Advanced mode stabilization tools and diagnostics for DEFC
RWM suppression
• Unique tools for understanding core and edge transport and
turbulence
– Excellent laboratory in which to study core electron transport
• Uniquely able to mimic ITER fast-ion instability drive with full
diagnostics
• Developing understanding and unique tools for heat flux and
particle control
• Non-inductive startup schemes utilizing CHI, EBW, HHFW being
developed
– Understanding of EBW/HHFW coupling essential
SMK – LLNL
39
Backup Vugraphs
SMK – LLNL
40
STs Can Lead to Attractive Fusion Systems
•
•
SMK – LLNL
Component Test Facility (CTF) will be needed after ITER to carry out
integrated DEMO power testing and development
ST enables highly compact CTF with full remote maintenance and high
duty factor, and it provides potentially attractive reactor configuration
Peng et al, PPCF 47, B263 (2005)
41
NSTX Facility/Diagnostics Upgrades in FY’06
• Lithium Evaporator for improved particle recycling control
• Feedback capability for EF/RWM coils powered by SPAs
• 12 channels for MSE diagnostic to improve j(r) determination
• Higher voltage operation of CHI for record current ~ 160 kA
• Dual remotely steerable, obliquely viewing 8-40 GHz EBW
radiometers
• TF joints operated reliably up to 5.5 kG
SMK – LLNL
42
Error Field Correction by External Coils Extended
Duration of High-Performance Plasmas
48 Internal
BP, BR sensors
6 External
Control Coils
Plasma rotation sustained by
correction of intrinsic error fields
Copper
stabilizing
plates
NSTX
2
ITER
Control coils
Stabilizing
plates
Blanket
modules
Z(m)
1
0
-1
-2
0
ITER shape
boundary
vessel
1
2
R(m)
SMK – LLNL
J. Menard et al., IAEA 2006
43
Observed Rotation Follows Neoclassical Toroidal
Viscosity (NTV)Theory
Magnetic braking due to
applied n=3 field
• First quantitative
agreement with NTV
theory
– Due to plasma flow
through nonaxisymmetric field
– Trapped particle, 3-D
field spectrum important
– Computed using
experimental equilibria
Zhu et al., PRL 96 (2006) 225002
SMK – LLNL
• Viable physics for
simulations of rotation
dynamics in future
devices (ITER, CTF)
44
Increased Ion Collisionality Leads to Decreased Wcrit
• Plasmas with similar vA
• Consistent with neoclassical
viscous dissipation model
– at low g, increased ni leads to
lower Wcrit
121071
121083
Wcrit (km/s)
(a)
(K. C. Shaing, Phys. Plasmas 11 (2004) 5525.)
• ITER plasmas with lower ni may
require higher degree of RWM
active stabilization
vA (km/s)
(b)
nii (kHz)
Further analysis aims
to uncover RWM stabilization physics
(c)
Sontag, et al., IAEA 2006
SMK – LLNL
45
Low A, High b Favorable for NTM Seeding / Stabilization
Study
• Several modes (e.g. sawteeth*, RWMs**)
seed low frequency MHD modes in NSTX
Sawtooth excitation of n = 2
– Can led to soft beta limit, or plasma rotation
reduction resulting in disruption
– Large q = 1 radius, high b, mode coupling at
low-A makes seeding process easier
– NTM stabilization effects amplified at low-A
(GGJ  3/2) – NTM less deleterious
n=1
• NTM study planned 2007 - 2009
– Characterize modes: are these NTMs, TMs,
or internal kinks?
– Exploit 12 channel MSE, reflectometer, fast
multi-filter USXR capabilities
– Mitigate deleterious effects of modes
*Fredrickson, et al., Bull. Am. Phys. Soc. 2004
**Sabbagh, et al., NF 44 (2004) 560
SMK – LLNL
• Sawtooth excites n = 2, but n = 2 can
decrease post-crash
46
Rotation profile shape important for RWM stability
– predicted by Bondeson-Chu semikinetic theory**
0.20
Wcrit/wA
• Benchmark profile for
stabilization is wc = wA/4q2 *
0.25
1/(4q
2
)
Wcrit/wA
0.00
1.5 2.0 2.5 3.0 3.5 4.0
q
0.4
*A.C. Sontag, et al., Phys. Plasmas 12 (2005) 056112
**A. Bondeson, M.S. Chu, Phys. Plasmas 3 (1996) 3013
SMK – LLNL
0.10
no applied field
n=3
n = 3 max. braking
tcrit - 10 ms
0.05
• High rotation outside q = 2.5 not
required for stability
• Scalar Wcrit/wA at q = 2 , > 2 not
a reliable criterion for stability
– consistent with distributed
dissipation mechanism
0.15
Sontag, IAEA 2006
no applied field
n = 3 DC
n = 1 DC
n = 1 traveling
n=1&n=3
2
1/4q
0.3
0.2
0.1
0.0
1.0
2.0
3.0
q
4.0
47
New Diagnostic Capabilities Have Facilitated
Progress in Understanding Transport Processes
51-point CHERS
20-point MPTS
12 channel MSE [NOVA Photonics]
LRDFIT
Reconstruction
Rmag
Important for equilibrium and
microinstability calculations
Tangential microwave scattering measures
localized electron-scale turbulence
• kr=2 (upper ITG/TEM) to ~24 (ETG) cm-1
• re ~0.01 cm
• Dr ~ 6 cm
• Dk ~ 1 cm-1
• Can vary location of scattering volume
(near Rmag to near edge)
SMK – LLNL
48
Theory/Gyrokinetic Calculations Suggest ETG May Play an
Important Role in Determining Electron Transport at Low BT
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
Non-linear simulations indicate formation of
radial streamers (up to 200re): FLR-modified
fluid code [Horton et al., PoP 2005]
GS2
0.35 T
Good agreement between experimental
and theoretical saturated transport level
at 0.35 T
SMK – LLNL
Qe (kW/m2)
Kim, IFS
TRANSP
Saturated
ETG level
49
New Diagnostic Capabilities Have Facilitated
Progress in Understanding Transport Processes
12 channel MSE [NOVA Photonics]
Tangential micorwave scattering measures
localized electron-scale turbulence
• kr=2 (upper ITG/TEM) to ~24 (ETG) cm-1
• re ~0.01 cm
• Dr ~ 6 cm
• Dk ~ 1 cm-1
• Can vary location of scattering volume
(near Rmag to near edge)
LRDFIT
Reconstruction
Important for equilibrium and
microinstability calculations
SMK – LLNL
50
Dimensionless Parameter Scans Have Addressed
High-Priority ITPA Issues
b-scan at fixed q, BT
- b-dependence important to ITER
advanced scenarios (Bt98y2~b-0.9)
- Factor of 2-2.5 variation in bT
- Degradation of tE with b weak on NSTX
ne*-scan at fixed q
- Factor of >3 variation in ne*
- Strong increase of confinement with
decreasing collisionality
20% variation in re, ne*
k=2.1
d=0.6
SMK – LLNL
51
15.5 GHz
(fce)
0.6
EBW/HHFW Coupling
Studies Being Carried Out
Conversion
0.4 Efficiency
uncertainty
B-X-O
mode coupling
understood
Simulated
Trad 0.2 in
L-mode at fce; coupling
inradH-mode low
Measured T
0
2
0
1.0
15.5
GHz
25 GHz
(fcece) )
(2f
0.8
0.6
L-mode
T
Trad
rad 1
1
Simulated
[keV]
[keV]
Trad
uncertainty
0
20
Conversion
Conversion
Efficiency
0.4 Efficiency
uncertainty
Measured Trad 0.2
Simulated
Measured Trad
0
1.0
0.2
0.4
Measured EBW
0.8Coupling Efficiency
25 GHz Time[s]
(2fce)
0.6
Trad
1
[keV]
Trad 0.4
Simulated
Trad
0
0
0
0
SMK – LLNL
0.6
H-mode
0.2
0.2
0.4
Time[s]
0.4
0.6
Time [s]
20%
0.2
0
0.8
P1560
k||=3
30%
15.5 GHz
Conversion
(f0.4
ce ) Efficiency
uncertainty
Measured Trad
[keV]
0.2
HHFW htg efficiency improved at high BT and k||
BqRF (au)
Trad
1
[keV]
0.8
0%
P1554
PRF = 2 MW
0.02
0.02
7 m-1
0.01
0.01
14 m-1
10%
1.0
P1558
m-1
0
0.1
0.15
0.1
0.2
0.2
Time (sec)
0.25
52
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, BT?)
• Data provided to ITPA H-mode database for R/a and bT scalings
– No degradation of BtE with bT
•
~
n/n decreases from L- to H-phase for kr=2
to 24 cm-1 (upper ITG/TEM to ETG range)
– Associated with reduction in transport
•
Linear and non-linear theory have
indicated ETG modes could be important
– Need also to consider lower-k modes
(microtearing, ITG/TEM)
SMK – LLNL
53
Pellet Perturbations Are Being Used to Probe
Relation of Critical Gradient Physics to q-Profile
Soft X-ray array
diagnoses fast DTe
R/LTe
t=440→444 ms
H-mode with
monotonic q-profile
exhibits stiff profile
behavior
→ Te close to marginal
stability
R/LTe
t=297→301 ms
Reversed magnetic
shear L-mode responds
to pellet perturbation
over several ms
Stutman, JHU
SMK – LLNL
54
Heat and Particle Flux Control is an Important Issue
for the ST (High Divertor Power Loading, P/R)
Peak heat flux increases with power,
with a change in slope at ~2.5 MW
Midplane heat flux SOL much broader
in NSTX than models would predict
lqSOL, m-p (cm)
Conduction Dominated
Divertor
Radiation Dominated
Divertor
collisionless
Counsell
collisional
(assuming 100% power accountability)
SMK – LLNL
PLoss (MW)
Kallenbach
55
Peak Heat Flux Can Be Reduced By Plasma Shaping
• Flux expansion decreases peak heat flux
despite reduced major radius
• Compare single-null & double-null
configurations with triangularity d ≈ 0.4 at
X-point and high triangularity d=0.8
double-null plasmas
– Measure heat flux with IR
thermography of carbon divertor tiles
• Peak heat flux decreases as 1 : 0.5 : 0.2
• ELM character changes: Type I  Mixed
 Type V
SMK – LLNL
56
Gas Puffing Near X-point Can Reduce Peak Heat
Flux With No Loss of Confinement
V. Soukhanovskii, IAEA 2006
SMK – LLNL
57
Lithium Coating Effects
SMK – LLNL
58
Coaxial Helicity Injection (CHI) has convincingly demonstrated
the formation of closed poloidal flux at high plasma current
Evidence for high-IP flux closure:
•
IP=160kA remains after
CHI injector current ICHI  0
at t=9ms
•
After t=9ms, plasma current
decays away inductively
•
Once IINJ 0, reconstructions track dynamics of detachment & decay
SMK – LLNL
59
ELM Suppression Using EF/RWM Control Coils
Being Investigated
• Suppression of ELMs with Resonant
Magnetic Perturbations
– ITER Decision needed soon on
internal versus external coils
• Data is desired from the NSTX
EF/RWM coil to assess external coils
– Experiment in 2005 showed possible
periods of ELM suppression
– Improved NSTX modeling since
2005, success on JET w/ n=1
• Integration of radiative & dissipative
divertors
– Outer divertor heat flux reduction
with divertor D2 , CD4 or N2 puffing
SMK – LLNL
60
Fully Non-Inductive Scenario at Higher bN Requires
Higher Confinement, Higher q, Strong Plasma Shaping
Target
Experiment
(116313)
• Higher k for higher q, bP, fBS
• High d for improved kink stability
k= 2.3, dX-L = 0.75
dRSEP = -1cm
k= 2.6, dX-L = 0.85
dRSEP = -2mm
• Need 60% higher T, 25% lower ne
• Higher q0  qmin  2.4 (higher with-wall
limit bN < 7.2)
SMK – LLNL
61
Stable & Fully Non-Inductive Target Scenario Utilizing
Only NBI and BS Current Drive Has Been Identified
Present high-fNI long-pulse H-modes:
Ip = 750kA
 bN < 5.6, bpol < 1.5, bT < 17%
li = 0.6, qmin=1.3, BT=4.5 kG
 k = 2.3, dX-L = 0.75, q*=3.9
Inductive current drive is replaced by:
Target scenario:
Ip = 700kA
bN = 6.7, bpol = 2.7, bT =15%
li = 0.5, qmin = 2.4, BT=5.2 kG
k = 2.6, dX-L = 0.85, q*=5.6
Higher JNBI from higher Te
Higher JBS from higher bP-thermal
Self-consistent
JTOT from TRANSP
SMK – LLNL
62
MHD-Induced Redistribution of NBI Current Drive Contributes
to NSTX “Hybrid”-Like Scenario Proposed for ITER
qmin>1 for entire discharge, increases during late n=1 activity
• Fast ion transport converts
peaked JNBI to flat or hollow profile
• Redistribution of NBICD makes
predictions consistent with MSE
n=1 mode onset
n=1 mode onset
• High anomalous fast ion transport needed to
explain neutron rate discrepancy during n=1
SMK – LLNL
J. Menard, PRL 97, 095002 (2006)
63
FY 07 Facility Enhancements
• Higher temperature bakeout of divertor tile to improve plasma performance and to
prepare for lithium
– Lower divertor tiles to 350°C and upper tiles to 300°C
• Improved restraint of OH-TF coils to reduce n=1 error field
– Spacers installed
• Higher pressure for supersonic gas injector to improve fueling for
H-mode (LLNL)
• Faster lithium evaporation ~ x10 with improved aiming to lower divertor plates
– Evaporation between/during shots in normal cycles
– Shields installed to protect MPTS and high-k windows
• Higher voltage for higher current CHI (U Washington)
– Upgrading charging power supply
– Improved voltage monitoring
– Dynamo edge probe (UCSD)
• Faster processors for real-time plasma control system to replace obsolete
components (GA)
– Aiming to be ready to operate in parallel by end of FY07 run
SMK – LLNL
64
FY 07 Diagnostic Enhancements
• Poloidal CHERS (27 ch) for transport physics
• MSE 12  16 channels for improved j(r) resolution (Nova)
• Transmission grating x-ray spectrometer viewing across NBI for impurity transport
(JHU)
• FIDA (Fast Ion Da measurement) - a few fast, band-pass-filtered channels for the
local fast-ion density (late in the run) (UC Irvine)
• FIReTIP 4  6 channels (500 kHz) for improved spatial resolution (UC Davis)
• New collection mirror for high-k scattering system
• Correlation reflectometer, fixed freq. reflectometer (3  6 ch), profile reflectometer
(25  10ms) and high-k backscattering (late in the run) (UCLA)
• Improved high-frequency Mirnov coil system for energetic particle modes and
segmented Rogowski coil for disruption study
• Wider-angle view and gas-puffing for EBW radiometers for H-mode coupling
• 3 RF probes to measure surface waves during HHFW heating
• Additional divertor filterscope fast channels (24-32 total) (ORNL)
SMK – LLNL
65