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 151-742, Korea, email:brbbebbero@snu.ac.kr 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 > 1014 [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