Introduction to Spherical Tokamak
SUNISTSUNIST
for 4th Workshop on Nonlinear Plasma Sciences & International School on Plasma Turbulence and Transport
Hangzhou 2005
GAO, ZheDepartment of Engineering PhysicsTsinghua University, Beijing [email protected]
OUTLINE
• What is the spherical tokamak?
• ST advantage
• ST worldwide
• New physics of toroidal plasmas
• Potential contribution
• What is the Spherical Tokamak?
Spherical tokamak
Spherical torus tokamak
Spherical tokamak=low aspect ratio tokamak
Aspect ratio, A=R/a
ST in Fusion configuration family
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The first ST: START
• AdvantageCompact configuration
Natural elongation
Large qa n r si c ea e t n y o toro l l (he efficie c f ida fie d
ypyyrod yy>
large plasma current
lower toroidal field (paramagnetism)
High β
High density limit
Less major disruption (instead of IREs)
Good energy confinement
Improved confinement mode achieved
• ST worldwide
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Parameters achieved
MAST NSTX
major radius R (m) 0.7 0.85
minor radius a (m) 0.5 0.68
elonggation κ 2.45 2.2
aspect ratio A (R/a) 1.3 1.27
plasma current IP (MA) 1.35 1.5
toroidal field BT(R0) (T) 0.52 0.6
neutral beam power PNBI (MW) 3.3 7
RF power P (MW) 1.5 ECRH HHFW 6
pulse length (s) 0.7 1.1
• Extended toroidal plasmas & New Physics(1) elongation>3, Bp/Bt~1, β~40%, Vrotation/Valfven~0.3
High βy l r r rot t ony stron s p qu la ge a i g ha ed e i
r umib i
(2) High β, low Valfven,, strong shear γE*B~106/s
yl trom n t tur ul n n ec ag e ic b e ce a dtr nporta t low ya
(3) a/ρi~30-50, a/ρfast ion~3-10, near omnigeneity, strongly mag well
Neoclassical transport at low A
(4) Valfven ～ Vs, Vfast ion>>Valfven ,less damping on TAE
st on p ys sFa i h ic
(5) High dielectric constant (ωpe2/ ωce
2~50-100)
y v yp rt l nt r t on (R t n a e a ic e i e ac i F hea i gyy yD
(6) Narrow inner regions and Low li yol no y r st rtupe idfe e a
Topical Research Plan of ST ( NSTX Five Year Plan)• MHD: RWM active and passive stabilzation
Fast-ion MHD (Alfven like)
NTM (stabilization by RF)
High beta equilibrium
• Transport and turbulence: high k and low k turbulence
H mode
Electron thermal barriers
Aspect ratio scaling
• Wave-plasma interaction: HHFW, EBW
• Solenoid-free startup: Transient CHI, PF induction, RF(ECH/EBW)
• Boundary Physics: Li conditioning, SOL transport
• Integration
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• What might ST bring to fusion application ？
Contribute to AT & burning plasma (ITER) physics
• Advanced Tokamak concept
High plasma kinetic pressure
Good confinement
High self-sustained current
(Quasi-) Stationary state
Advance fuel recycle
• Burning plasma
Other application:
VNSCTFContribution to AT and burning plasma researchSpace propulsion
Future Steps
Tokamak
* T-3, T-4, ST etc. 1970’s
** PLT, ASDEX etc.later 70’s
***TFTR,JET, JT-60U, 80—90‘s
**** ITER
2100’s
SUNIST: Sino United Spherical Tokamak
major radius R 0.3m
minor radius a 0.23m
Aspect ratio A ~1.3
elongation κ ~1.6
toroidal field （ R0） BT 0.15T
plasma current IP 50kA
central rod current IROD 0.225MA
flux (double swing) ΔΦ 0.06Vs
• AcknowledgementCollecting material from the following references:
Peng Y-K, STW2004, Kyoto.
Gryaznevich M, STW2004, Kyoto.
Peng Y-K, STW2003, Culham.
Peng Y-K, Phys. Plasmas 2000, 7(5): 1681.
Sykes A, Nucl. Fusion 1999, 39(9Y):1271.
NSTX team, NSTX five year research plan
Peng Y-K and Strikler DJ, Nucl. Fusion 1986, 26:576
and many ST Websites.
TOKAMAK
Spheromak
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ST: more compact
ST: natural elongation
ST: High qa
ST: high beta
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ST: high density
ST: more stable for VDI Internal Reconnection Event (IRE)
• ST: good confinement
High beta equilibrium with larger rotation
turbulence and transport
Single particle motion in ST
HHFW CD
EBW CD
Diffusion near the T-P boundary
CHI startup
Outer Poloidal Field startup
• ECH startup
• Bootstrap current MAST (real discharge) NSTX (Theo prediction)
• Divertor configuration
Divertor configurations in MAST:
Double-Null Divertor (DND)
Limited, or Natural Divertor (ND)
Single-Null Divertor(SND)
H-mode in DND and Natural Divertor plasmas
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