Progress towards high performance, steady-state Spherical Torus

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Progress towards high performance, steady-state
Spherical Torus
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, Garching IPP,
Jülich U Quebec
Masayuki Ono Princeton University, USA For the
US Spherical Torus Program (NSTX, PEGASUS,
HIT-II, CDX-U, Theory) Paper I.4-4 EPS 2003 St.
Petersburg, Russia July 7 - 11, 2003
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Spherical Torus Offers High b Plasmas with Strong
Toroidicity High Safety Factor (qedge 10)

• Extended Physics parameter space available for
  plasma science
• High ltbTgt( 40) central b0 (100)
• Strong plasma shaping self fields (A ?1.27, d
  0.8, k ? 2.5, Bp/Bt 1)
• Small plasma size relative to gyro-radius (a/ri
  3050)
• Large plasma flow (Vrotation/VA 0.3)
• Large flow shearing rate (?ExB ? 106/s)
• Supra-Alfvénic fast ions (Vfast/VA 45)
• High dielectric constant (e 50)
• Large mirror ratios in edge B field

Spherical Torus provides interesting plasmas
M. Y-K. Peng, D.J. Strickler, Nuclear Fusion 26
(1986) 576.
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The Cost-Effective Steps to Fusion Energy
Device NSTX NSTX NSST NSST CTF CTF DEMO
Mission Proof of Principle Proof of Principle Performance Extension Performance Extension Energy Development, Component Testing Energy Development, Component Testing Practicality of Fusion Electricity
R (m) 0.85 0.85 1.5 1.5 1.2 1.2 3.4
a (m) 0.65 0.65 0.9 0.9 0.8 0.8 2.4
k, d 2.5, 0.8 2.5, 0.8 2.7, 0.6 2.7, 0.6 3, 0.4 3, 0.4 3.2, 0.5
Ip (MA) 1.5 1 10 5 11 11 30
BT (T) 0.6 0.3 2.6 1.1 2.2 2.2 1.8
Pulse (s) 1 5 5 50 Steady state Steady state Steady state
Pfusion (MW) - - 50 10 70 280 3000
WL (MW/m2) - - - - 1 4 4
TF coil multi-turn multi-turn multi-turn multi-turn single-turn single-turn single-turn
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SCIENTIFIC CHALLENGES OFHIGH PERFORMANCE
STEADY-STATE OPERATIONS

• MHD Stability at High bT and bN Fusion power
  at low toroidal field with high bootstrap current
  fraction.
• bT 20, bN 6 for CTF
• bT 40, bN 8 for Power Plants (advanced
  regime)
• Transport and Confinement High performance at
  small size.
• H98pby,2 1.4 - 1.7 with good electron
  confinement required.
• Power and Particle Handling Small major radius
  increases P/R by a factor of 2 to 3.
• Solenoid-Free Start-Up Elimination of solenoid
  required for compact reactor design.
• Integrating Scenarios Putting it all together.
  

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The US ST Research is a part of the Worldwide
Effort.
Extreme Low A, HHFW, EBW, Spheromak Comp.
CHI Synergy
Cu Shell, Mode Control, CHI, NBI, HHFW,
EBW, Particle Control
HIT-II
Pegasus
NSTX
LHW, NBI, Advanced Diagnostics
Extreme Low A, CHI, Spheromak
ECH startup, HHFW Innovation
Globus-M
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NSTX Designed to Study High-TemperatureToroidal
Plasmas at Low Aspect-Ratio
Achieved Parameters Aspect ratio
A 1.27 Elongation ? 2.2 Triangularity ? 0.8 Major
radius R0 0.85m Plasma Current Ip 1.5MA Toroidal
Field BT0 0.6T Solenoid flux 0.7Vs Auxiliary
heating current drive NBI (100kV) 7 MW RF
(30MHz) 6 MW CHI 0.4MA Pulse Length 1.1s
Experiments started in Sep. 99
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PEGASUS
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MHD Stability at High bT and bN
Related papers J. Menard, et at, P-3.101 E.
Fredrickson, P-3.99 N. Gorelenkov et al.,
P-3.103 E. Belova et al., P-3.102
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Steady-state ST requires both high bT and bP

• Self-driven current fraction ? bP ? 2m0?p? / BP2
• bT ? bN2 / bP ? Need very high bN for steady
  state

• NSTX bT40
• Target equilibria
• High bT and bN
• High bP and bN
• Want q ? 2-3 at high bN gt 8

(reduced error fields)
2002 data 2001 data
bP / A
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High beta maintained for duration gt tE
?T 35
H mode
tE

• H-mode routine access
• broadens pressure profile
• bN 5.5, li 0.6

BT 0.3T, A 1.4 ? 2.0, ? 0.8 q(0) 1.4
(EFIT)
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PEGASUS
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High Fraction of Non-Inductive Currents Achieved
in Long-Pulse High bpol Discharges

• INI Fraction 60
• bN 5.8 gt no-wall stability limit
• bN H89p 15 at bT 15 sustained over
  t-skin.

NSTX Long pulse CTF base case ARIES-ST
bT 15 20 50
bN 5 5 8
bp 1.2 1 1.4
qcyl 3.2 3 3
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NSTX Accesses vFast gt vAlfvén Physics Relevant
to ITER, ICCs and Future ST Devices

• n gt 1 modes interpreted to be TAE
• n 1 as bounce fishbones
• Transport of core fast ions by n2 mode
• Fast ions then destabilize n1, ions lost

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Transport and Confinement
Related papers B. LeBlanc, et at, P-3.98 R.
Maingi, et al., P-3.97 M. Redi, et al.,
P-4.94 D. Stutman, et al., P3.100
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Global Confinement Exceeds Predictions from
Conventional Aspect Ratio Scalings
tE,global
Quasi-steady conditions tE,global from EFIT
magnetics reconstruction - Includes fast
ion component tE,thermal determined from TRANSP
runs
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NSTX NBI L-modes Exhibit Similar Parametric
Scaling as Conventional Aspect Ratio Devices
tENSTX-L Ip0.76 BT0.27 PL-0.76
Accurate determination of R/a dependence is an
active ITPA research topic Less severe power
degradation in H-mode tE P-0.50 - H-mode
parametric dependencies complex
and non-linear
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Good Ion Confinement Suggests Suppression of
Long Wavelength Turbulence
Transport behavior of NBI heated NSTX discharges
Observed ordering cf lt ci ? cneo lt ce
ci cneo and cf lt ci suggest long wavelength
turbulence may be suppressed. ce has an
unusual profile.
Vrotation/VA 0.3
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Theory guides NSTX transport physics research

• Microstability and turbulence simulations are
  done with, FULL, GS2, GYRO. GTC
• GS2 linear analyses shows that
• ExB shearing rate stabilizes long l, ITG modes
• short l ETG modes not stabilized, may dominate
  transport
• Modes that are usually sub-dominant, (tearing
  parity), may play a role
• Diagnostics and localized heating, EBW, will test
  theory
• Non-linear studies GS2
• global (GTC GYRO) in future

NSTX can provide a unique test-bed to understand
electron transport and eventually to control it.
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Power and Particle Handling
Related paper V.A. Soukhanovskii, et at, P-3.179
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Peak heat flux increased with NBI power in LSN
and was reduced in DND relative to LSN
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CDX-U is investigating liquid lithium PFCs
Note reflections in metallic lithium
Filling technique developed by UCSD - PISCES
group.

• Oxygen, carbon impurities virtually eliminated
• Immediate 30 increase in peak Ip, discharge
  duration
• Loop voltage to sustain current dropped from 2.0
  ? 0.5V

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Liquid lithium could lead to revolutionary heat
and particle control techniques
Greatly reduced recycling
Oxygen virtually eliminated
2-3 x core Te

• ? Liquid lithium in toroidal limiter tray (250o
  C)
• ? Cold lithium in tray
• Bare stainless steel tray

CDX-U Plasma contacting surface area only 10
liquid lithium
NSTX is planning liquid lithium module in
collaboration with VLT(Virtual Laboratory for
Technology)
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Solenoid-Free Start-Up - Coaxial Helicity
Injection - Outer poloidal field start-up
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CHI Generated Large Toroidal Current in NSTX

• Goal is to control discharge evolution to promote
  relaxation of toroidal current into closed flux
  surfaces

NSTX Univ. of Washington, PPPL
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HIT-II developed a new CHI startup method

• CHI started discharges coupled to inductive
  discharges saved volt-seconds
• CHI started discharges much more robust and less
  sensitive to wall conditions
• CHI started discharges produced record plasma
  currents on HIT-II (265kA)

NSTX plans to test the CHI assisted OH start-up
concept.
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Outer Poloidal Field Coil Only Start-Up
In ST geometry, a qualify field null can be
formed by outer PF coils while retaining
significant flux for current ramp up.
NSTX plans to test poloidal field only start-up
concepts.
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Integrated High Performance Scenarios
To achieve ST reactor relevant physics
parameters 40 bT , INI 100, tpulse gtgt tskin
To be developed in NSTX
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40 bT , INI 100, tpulse gtgt tskin within reach
using the additional tools that are planned

• Enhanced shaping improves MHD stability
• - PF 1a modification to allow high k 2.4 and
  high d 0.8
• Near with-wall limit gt mode control rotation
• - Active feedback coils to be installed
• Particle control required to maintain moderate ne
  for CD
• - Divertor lithium wall coating and cryo-pump
  planned
• EBW provides off-axis CD to keep q 2
  stabilize NTMs
• - 4 MW 15 GHz EBW system planned
• 7 MW NBI CD, bootstrap current significant part
  of the total
• 6 MW HHFW heating contributes to bootstrap,
  raises Te

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Stability results motivate shaping enhancements
bN
bT ()
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High Harmonic Fast Wave Provides Heating and
Current Drivein High Dielectric e 50 ST
Plasmas
Electron heating demonstrated
HHFW current drive demonstrated

• Primary HHFW damping mechanism
• Observed over wide range in wave phase velocity
• Electron ITB created

• Differences in Vloop with co and counter-directed
  waves indicate 100 kA of current drive
  consistent with theoretical modeling

HHFW NBI interactions investigated. S. Medley
et al., P-3.96
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Electron Bernstein Wave Current Drive could
provide needed localized off-axis current drive

• EBW can drive localized current in overdense
  plasmas
• Supplement bootstrap current and stabilize NTMs
• Requires mode-conversion of coupled EM wave to
  EBW
• Characteristics of edge plasma are critical

• Small Ln at conversion layer
• Investigating with emission measurements in NSTX
• Including local edge profile modification
• Valuable input from CDX-U and MAST EBW programs

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ST RESEARCH IS MAKING RAPID PROGRESS

• MHD Stability at high bT and bN
• - 35 bT achieved on NSTX. - PEGASUS produced
  20 bT with just OH at low A 1.3.
• - bN H89p 15 at bT 15 sustained for tskin
  exceeded no-wall limits.
• Good confinement behavior H98pby,2 1.4 at
  high beta
• - Neo-classical ci correlates with plasma
  rotation (sheared flow stabilization).
• - Very low cf led to Vrotation 0.3 VA.
• Power and Particle Handling
• - High d 0. 8 configuration shows a large
  reduction in peak heat flux.
• - CDX-U has successfully tested liquid lithium
  limiter.
• Two Approaches for Solenoid-Free Start-Up
• - Coaxial helicity injection is pursued on NSTX
  with HIT-II collaboration
• - Outer-poloidal field coil start-up research is
  initiated.
• Integration - New shaping and profile tools are
  planned
• - High d 0.8, high k 2.4 with profile control
  and RWM stabilization could lead to the advanced
  ST regimes of 40 bT and 100 JNI.

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Thanks to the NSTX, CDX-U, HIT-II, PEGASUS and
Theory Teams

• M. Ono, M.G. Bell, R.E. Bell, T. Bigelow, M.
  Bitter, W. Blanchard, J. Boedo, C. Bourdelle, C.
  Bush, W. Choe, J. Chrzanowski, D.S. Darrow, S.J.
  Diem, P.C. Efthimion, J.R. Ferron, R.J. Fonck,
  E.D. Fredrickson, G.D. Garstka, D.A. Gates, L.R.
  Grisham, W. Heidbrink, K.W. Hill, J.C. Hosea,
  T.R. Jarboe, D.W. Johnson, R. Kaita, S.M. Kaye,
  C. Kessel, J.H. Kim, M.W. Kissick, S. Kubota,
  H.W. Kugel, B.P. LeBlanc, K. Lee, S.G. Lee, B.T.
  Lewicki, R. Maingi, R. Majeski, J. Manickam, R.
  Maqueda, T.K. Mau, E. Mazzucato, S.S. Medley, J.
  Menard, D. Mueller, B.A. Nelson, C. Neumeyer, N.
  Nishino, C.N. Ostrander, D. Pacella, F. Paoletti,
  H.K. Park, W. Park, S.F. Paul, Y.-K. M. Peng,
  C.K. Phillips, R. Pinsker, P.H. Probert, S.
  Ramakrishnan, R. Raman, M. Redi, A.L. Roquemore,
  A. Rosenberg, P.M. Ryan, S.A. Sabbagh, M.
  Schaffer, R.J. Schooff, C.H. Skinner, A.C.
  Sontag, V. Soukhanovskii, T. Stevenson, D.
  Stutman, D.W. Swain, E. Synakowski, Y. Takase, X.
  Tang, G. Taylor, K.L. Tritz, E.A. Unterberg, A.
  Von Halle, J. Wilgen, M. Williams, J.R. Wilson,
  X. Xu, S.J. Zweben, R. Akers, R.E. Barry, P.
  Beiersdorfer, J.M. Bialek, B. Blagojevic, P.T.
  Bonoli, M.D. Carter, W. Davis, B. Deng, L. Dudek,
  J. Egedal, R. Ellis, M. Finkenthal, J. Foley, E.
  Fredd, A. Glasser, T. Gibney, M. Gilmore, R.J.
  Goldston, R.E. Hatcher, R.J. Hawryluk, W.
  Houlberg, R. Harvey, S.C. Jardin, H. Ji, M.
  Kalish, J. Lawrance, L.L. Lao, F.M. Levinton,
  N.C. Luhmann, R. Marsala, D. Mastravito, M.M.
  Menon, O. Mitarai, M. Nagata, M. Okabayashi, G.
  Oliaro, R. Parsells, T. Peebles, B. Peneflor, D.
  Piglowski, G.D. Porter, A.K. Ram, M. Rensink, G.
  Rewoldt, P. Roney, K. Shaing, S. Shiraiwa, P.
  Sichta, D. Stotler, B.C. Stratton, R. Vero, W.R.
  Wampler, G.A. Wurden, X.Q. Xu, L. Zeng, W. Zhu