Supported by Columbia U Comp-X General Atomics Spherical Tokamak Plasma Science INEL Johns Hopkins U LANL LLNL & Fusion Energy Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL Martin Peng UC Davis UC Irvine UCLA NSTX Program Director UCSD U Maryland Oak Ridge National Laboratory U New Mexico U Rochester @ Princeton Plasma Physics Laboratory U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Second Japan-Korea Seminar on Advanced Tsukuba U U Tokyo Diagnostics for Steady-State Fusion Plasma JAERI Ioffe Inst TRINITI KBSI Korea Basic Science Institute (KBSI) KAIST ENEA, Frascati August 25-27, 2004 CEA, Cadarache IPP, Jülich Daejon, Korea IPP, Garching U Quebec JKS2004-Aug25-27/04 ST Science & Fusion Spherical Tokamak (ST) Offers Rich Plasma Science Opportunities and High Fusion Energy Potential • What is ST and why? • Scientific opportunities of ST • How does shape determine pressure? • How does turbulence enhance transport? • How do plasma particles and waves interact? • How do hot plasmas interact with walls? • How to supply magnetic flux without solenoid? • Contributions to burning plasmas and ITER • Cost-effective steps to fusion energy • Collaboration JKS2004-Aug25-27/04 ST Science & Fusion Tokamak Theory in Early 1980’s Showed Maximum Stable βT Increased with Lowered Aspect Ratio (A) • A. Sykes et al. (1983); F. Troyon et al. (1984) on maximum stable toroidal beta βT: βTmax = C Ip / a 〈B〉≈5 C κ / A qj; 〈B〉≈BT at standard A C ≈ constant (~ 3 %m·T/MA) ⇒βN Z Plasma 〈B〉 = volume average B ⇒ B Cross T Section κ = b/a = elongation b A = R /a = aspect ratio a a 0 0 R R qI ≈ average safety factor 0 Ip = toroidal plasma current BT ≈ applied toroidal field at R0 • Peng & Strickler (1986): What would happen to tokamak as A → 1? − How would βN, κ, qj, change as functions of A? JKS2004-Aug25-27/04 ST Science & Fusion Minimizing Tokamak Aspect Ratio Maximizes Field Line Length in Good Curvature ⇒ High β Stability Good Curvature Bad Curvature Magnetic Surface Magnetic Field Line Spherical Tokamak (ST) Tokamak Compact Toroid (CT) Small-R close to Tokamak & large-R close to CT. JKS2004-Aug25-27/04 ST Science & Fusion ST Plasma Elongates Naturally, Needs Less TF & PF Coil Currents, Increases Ip/aBT, and Increases βTmax Natural Elongation, κ Small Coil Currents/Ip (qedge~2.5) A = 1.5 A = 2.5 ITF / Ip κ≈2.0 κ≈1.4 (~aBT / Ip) Z ΣIPF / Ip κ 0 RRST ATokamak • Naturally increased κ ~ 2; ITF < Ip, IPF < Ip ⇒ higher Ip; lower device cost • Increased Ip/aBT ~ 7 MA/m·T ⇒βTmax ~ 20%, if βN ~ 3 • Increased Ip qedge /aBT ~ 20 MA/m·T ⇒ improved confinement? JKS2004-Aug25-27/04 ST Science & Fusion Very Low Aspect Ratio (A) Introduces New Opportunities to Broaden Toroidal Plasma Science How does shape determine pressure? ST Plasmas Extends • Strong plasma shaping & self fields Toroidal Parameters (vertical elongation ≤ 3, Bp/Bt ~ 1) • Very high βT (~ 40%), βN & fBootstrap A = R/a can be ≥ 1.1 How does turbulence enhance transport? • Small plasma size relative to gyro-radius (a/ρi~30–50) • Large plasma flow (MA = Vrotation/VA ≤ 0.3) 6 • Large flow shearing rate (γExB ≤ 10 /s) How do plasma particles and waves interact? • Supra-Alfvénic fast ions (Vfast/VA ~ 4–5) 2 2 • High dielectric constant (ε = ωpe /ωce ~ 50) How do plasmas interact with walls? • Large mirror ratio in edge B field (fT → 1) • Strong field line expansion How to supply mag flux without solenoid? START – UKAEA Fusion • Small magnetic flux content (~ liR0Ip) JKS2004-Aug25-27/04 ST Science & Fusion ST Research Is Growing Worldwide Concept Exploration (~0.3 MA) Proof of Principle (~MA) HIT-II (US) Pegasus (US) MAST (UK) Globus-M NSTX (US) Pegasus MAST HIT-II START Proto-Sphera TS-3,4 HIT-I NSTX SUNLIST TST-M CDX-U HIST, LATE ETE Rotamak-ST CDX-U (US) Globus-M (RF) ETE (B) SUNIST (PRC) HIST (J) TST-2 (J) TS-4 (J) TS-3 (J) JKS2004-Aug25-27/04 ST Science & Fusion Pegasus Explores ST Regimes As Aspect Ratio → 1 JKS2004-Aug25-27/04 ST Science & Fusion NSTX Exceeded Troyon Scaling at Higher Ip/aBT Indicating Better Field and Size Utilization at Low A • Obtained high beta values: NSTX Design & Operation Goals 2 βT =2µ0〈p〉 /BT0 ≤ 38% βN = βT / (Ip/aBT0) ≤ 6.4 2 〈β〉 = 2µ0〈p〉 / 〈B 〉≤20% fBS ~ 70% • To produce and study full non- β ~ 8 N inductive sustained plasmas fBS ≤ 50% – Relevant to DEMO βN ≤ 6 • Nearly sustained plasmas with neutral beam and bootstrap current – Relevant to ITER hybrid mode – Nearly basis for neutral beam sustained ST Component Test Facility (CTF) at Q~2 JKS2004-Aug25-27/04 Columbia U, LANL, PPPL ST Science & Fusion Detailed Measurements of Plasma Profiles Allows Physics Analysis and Interpretations Plasma Flow Shearing Rate up to ~106 /s JKS2004-Aug25-27/04 ST Science & Fusion Strong Plasma Flow (MA=Vφ/VAlfvén~0.3) Has Large Effects on Equilibrium and Stability Equilibrium Reconstruction • Internal MHD modes with Flow stops growing pressure surfaces 2 • Pressure axis shifts magnetic surfaces out by ~10% of outer minor radius • Density axis shifts by 1 ~20% 107540 1.4 T (keV) 0 e 330ms Z(m) 1.2 1.0 0.8 -3 -1 0.6 ne (m ) 19 0.4 4x10 MA 0.2 0.0 0.4 0.6 0.8 1.0 1.2 1.4 -2 R(m) 0.51.0 1.5 2.0 Columbia U, GA, PPPL, U Rochester R(m) JKS2004-Aug25-27/04 ST Science & Fusion High-Resolution CHERS, SXR, and In-Vessel BR and BP Sensors Reveal Strong Mode-Rotation Interaction In-vessel sensors measure SXR shows rotating 1/1 rotating mode as vφ decays mode during v decay CHarge-Exchange Recom- before mode locking φ bination Spectroscopy (CHERS) shows vφ collapse preceding β collapse Aliased n=1 rotating mode 1/1 Island Sabbagh, Bell, Menard, Stutman RWM, NTM, 1/1 modes, and rotation physics of high interest to ITER JKS2004-Aug25-27/04 ST Science & Fusion Active Control Will Enable Study of Wall Mode Interactions with Error Fields & Rotation at High βT ) -1 Vacuum Vessel Conducting Plates Resistive Wall Mode Growth Rate (s Internal Sensors Columbia U, GA, PPPL JKS2004-Aug25-27/04 ST Science & Fusion Global and Thermal τE’s Compare Favorably with Higher A Database 0.10 120 H-mode .5 L-mode 2 x .5 80 x1 (ms) [s] 0.05 <mag> E τ 40 <thermal> E τ 0.00 0 0.00 0.01 0.02 0.03 0.04 0.05 0 40 80 120 τ <ITER-97L> [s] <ITER-H98p(y,2)> E τE (ms) • Compare with ITER scaling for total • TRANSP analysis for thermal confinement, including fast ions confinement L-modes have higher non-thermal component and comparable τE! Why? JKS2004-Aug25-27/04 Bell, Kaye, PPPL ST Science & Fusion Ion Internal Transport Barrier in Beam-Heated H-Mode Contrasts Improved Electron Confinement in L-Mode iITB? Transport Kinetic Profile Local Error Sampling Barrier region where NC χi ~ χi Regions requiring and improved χe >> χi data resolution iITB? Axis Edge But L-mode plasmas show improved electron confinement! Why? ) L-mode 3 H-mode /cm 13 L-mode (keV) Magnetic Axis e H-mode (10 T e n JKS2004-Aug25-27/04 Columbia U, Culham, ORNL, PPPL ST Science & Fusion Analysis Shows Stability to Modes at Ion Gyro-Scale & Strong Instability at Electron Gyro-Scale (H-Mode) ) 3 Core Transport In ion confinement MHD event Physics zone Ne 8,9+ Thermal • χion ~ χneoclassical Conductivity • χelec >> χion Impurity •D ~ D (mW/cmEmissivity imp neoclassical R ( Diffusivity cm ) ) t (ms • Driven by T and n Micro- uff Ne p instability gradients iITB? calculations •kθρi < 1 (ion gyro- scale) stable or suppressed by Vφ shear •kθρi >> 1 (electron gyro-scale) strongly unstable JKS2004-Aug25-27/04 Cadarache, JHU, PPPL, U. Maryland ST Science & Fusion In MAST, However, Counter NBI Reduces Electron Energy Loss Co-NBI Counter-NBI 1.5 5 1.5 5 High flow shear scenario on T i MAST (Co- & Counter-NBI) 4 4 Te 1.0 n 1.0 • Counter-NBI produces stronger e ] 3 3 -3 ω ~ 106 s-1 and strong local m SE 19 [keV] 2 2 reduction in χe at broader radius 0.5 0.5 [10 • Pressure gradient contribution to 1 1 Er reinforces that due to Vφ with .2 s #8302, 0.2 s 0.0 0 0.0 0 ctr-NBI 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 ρ ρ • Strong ExB flow shear and weak 100 100 magnetic shear s ~ 0 produced #88575, 0.2 s #8302,#830 0.2 s by NBI heating during current ramp 10 10 ] -1 • With co-NBI ion thermal transport s 2 NC reduced to N.C. level χi ~ χi [m 1.0 1.0 with weaker reduction in χe χ χφ i • Strong ExB flow shear ωSE > χ χ NCN e i γ ITG and s ~ 0 at minimum of χ 0.1 0.1 m i,e 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 ρ ρ JKS2004-Aug25-27/04 ST Science & Fusion Detailed Diagnosis and Gyrokinetic Analysis of β ~ 1 Turbulence Has Broad Scientific Importance Can k¦ρι ≥ 1 turbulence at β ~ 1 be understood? Armitage (U. Colorado) Region to be tested Gyrokinetic turbulence simulation in accretion disk of supermassive black hole at galactic center, assuming damping of turbulence by plasma ions vs.