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 100084gaozhe@tsinghua.edu.cn

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