1. Introduction to Spherical Tokamak
SUNIST
for 4th Workshop on Nonlinear Plasma Sciences
& International School on Plasma Turbulence and Transport
Introduction to Spherical Tokamak
GAO, Zhe
Department of Engineering Physics
Tsinghua University, Beijing
Hangzhou

2. OUTLINE
What is the spherical tokamak?
ST advantage
ST worldwide
New physics of toroidal plasmas
Potential contribution

3. What is the Spherical Tokamak?

4. Spherical tokamak =low aspect ratio tokamak
Aspect ratio, A=R/a

5. ST in Fusion configuration family

6. UNIST
SUNIST
The first ST: START

7. Advantage Compact configuration Natural elongation
Large qaincrease the efficiency of toroidal field (Ip/Irod>1)
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

8. ST worldwide
SUNIST
SUNIST

9. toroidal field BT(R0) (T) neutral beam power PNBI (MW)
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)
1.1

10. Extended toroidal plasmas & New Physics
elongation>3, Bp/Bt~1, β~40%, Vrotation/Valfven~0.3
High β, larger rotation, strong shaped equilibrium
(2) High β, low Valfven,, strong shear γE*B~106/s
Electromagnetic turbulence and tranport at low A
(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
Fast ion physics
(5) High dielectric constant (ωpe2/ ωce2~50-100)
Wave-particle interaction (RF heating &CD)
(6) Narrow inner regions and Low li
Solenoid-free startup

11. Topical Research Plan of ST ( NSTX Five Year Plan)
SUNIST
UNIST
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

12. What might ST bring to fusion application？

13. Advanced Tokamak concept High plasma kinetic pressure
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

14. Other application:
VNS
CTF
Contribution to AT and burning plasma research
Space propulsion

15. 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

16. 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 kA
central rod current IROD 0.225MA
flux (double swing) ΔΦ 0.06Vs

17. Acknowledgement Collecting 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.

18. TOKAMAK

19. Spheromak

20. UNIST
SUNIST
ST: more compact

21. ST: natural elongation

22. ST: High qa

23. ST: high beta

24. UNIST
SUNIST
ST: high density

25. Internal Reconnection Event (IRE)
ST: more stable for VDI

26. ST: good confinement

27. High beta equilibrium with larger rotation

28. turbulence and transport

29. Single particle motion in ST

30. HHFW CD

31. EBW CD

32. Diffusion near the T-P boundary

33. CHI startup

34. Outer Poloidal Field startup

35. ECH startup

36. Bootstrap current
MAST (real discharge) NSTX (Theo prediction)

37. Divertor configuration
Divertor configurations in MAST:
Single-Null Divertor
(SND)
Double-Null Divertor (DND)
Limited, or Natural Divertor (ND)
H-mode in DND and Natural Divertor plasmas