1. Construction and Status of Versatile Experiment Spherical Torus at SNU
H.Y. Lee, Y.H. An, B.K. Jung, J.J. Yang, K.J. Chung and Y.S. Hwang
Dept. of Nuclear Eng., Seoul National Univ., 599 Gwanak-ro, Gwanak-gu, Seoul , Korea,
What is Fusion?
The way of Fusion
How can the sun and star generate the eternal energy?
Objectives for Fusion
Status & plan of fusion technology
Breakeven condition (Q≥1)
: JT-60(Japan), JET(Europe)
Self-ignition condition (Q ≥10)
: ITER, DEMO
Progress in fusion
: similar to computer & accelerator
How can we make two particle collide regardless of the repulsive force?
Available fusion reactor in following conditions.
High Temperature (T)
High Density (n)
High confinement (τ )
n x τ > [s/cm3]
D-T reaction
Ti ~15keV
Fusion reaction in the sun & star
Various fusion reactions in the universe
Confinement methods for Fusion – magnetic & Inertial
Magnetic confinement
Tokamak
Stellerator
D + T (reliable)
D + D  3He + n
D + 3He
T  4He + 2 n
3He + 3He  4He + 2 p
p + 11B  3 4He
 4He + n
Inner Poloidal field coils
(Primary transformer circuit)
Poloidal magnetic field
Outer Poloidal field coils
(for plasma positioning and shaping)
Without magnetic field
 T + p
 4He + p
+ T
Resulting Helical Magnetic field
Toroidal field coils
Plasma electric current
(secondary transformer circuit)
Toroidal magnetic field
Basic theory : magnetic field(B) => Confinement of charged particles
Two concepts of magnetic confinement : Tokamak, Stellerator.
Tokamak is simpler and has been studied more than Stellerator.
Pros and cons of Fusion
Inertial confinement
Abundant fuel, available to all nations : deuterium and lithium easily available for thousands of years
Environmental advantages : no carbon emissions, short-lived radioactivity
No change about external circumstances : weather, season etc.
Products (electricity & hydrogen) : eco-friendly fruits
Advantages
Disadvantages
Huge research and development costs
Radioactivity
Compressed fuel
: by blowoff of the hot surface
Ignition
: 20 times density
: 100,000,000ºC.
Thermonuclear burn
: yielding many times the input energy.
Laser beam
: rapidly heat the surface of the target
: form surface plasma
Spider man 2 – inertial confinement
ST as alternative concept
VEST Introduction
Schematic of VEST
* Elongation : 3.3 assumed
Partial Solenoid
Long Solenoid
TF Coils
Vacuum Chamber
Plasma
Merging
PF Coils
Breakdown
by Partial Solenoid
VEST : Versatile Experiment Spherical Torus
Objectives
Basic research on a compact, high- ST (Spherical Torus) with elongated chamber in partial solenoid configuration
Study on innovative partial solenoid start-up, divertor, non-inductive current drive etc.
Spherical Torus (ST) : Low aspect ratio (A<2) fusion device
Large aspect ratio
(Conventional Tokamak)
Small aspect ratio
(Spherical Torus) a R
Advantages
Weakness
High performance
: High β, High plasma current
Compactness
Difficulty in start-up & sustainment
due to the lack of space for solenoid
Specifications
Initial Phase
Future
Chamber Radius [m]
0.8 : Main Chamber
0.6 : Upper & Lower Chambers
Chamber Height [m]
2.4
Toroidal B Field [T]
0.1
0.3
Major Radius [m]
0.4
Minor Radius [m]
Aspect Ratio
>1.3
Plasma Current [kA] 30
100
Safety factor*, qa
7.4
6.7
Innovative start-up method is a critical issue for ST!
By developing new start-up and non-inductive CD methods,
ST can be a high performance fusion research device.
TF & PF Coil System
Parameters
Designed value
Measured value
Overall coil length [m]
2.7
Overall coil radius [m]
Inner: 0.07 / Outer: 1.1
Strand size [mm×mm]
Inner: 12×12 (f6 cooling) / Outer: 50×10
No. of turns [#] 24
Resistance [mW]
18.8
Inductance [mH]
0.93
Status of VEST
First plasma operation
Vertical stability &
Control of small plasma
Parameters
PF1
PF2
Coil length [m]
2.4
0.5
Coil radius [m]
In : 0.045
Out : 0.063
In : 0.08
Out : 0.125
Strand size [mm×mm]
3.5×16
No. of turns [#]
632
250
Resistance [mW] 68 52
Inductance [mH]
1.6
3.7
Maximum flux limit [V∙s]
0.13
0.55
Maximum current limit [kA] 27 14
Null formation
Null formation
PF3
PF4
Equilibrium
of small plasma
Partial solenoid
for plasma start-up
PF5
PF2
PF6
Vertical stability &
Control of small plasma
PF7
PF8
Long Solenoid for plasma sustaining
Null formation
First plasmas with Ip=2kA are generated ohmically
with ECH preionization
PF9
Equilibrium of
main plasma
23 June 2011
VEST successfully installed at SNU
PF10
PF1
Role of each PF coil
Construction and Status of Versatile Experiment Spherical Torus (VEST) at Seoul National University