Spherical Tokamak Plasma Science Comp-X General Atomics INEL - PowerPoint PPT Presentation

Supported by Columbia U Spherical Tokamak Plasma Science Comp-X General Atomics INEL Johns Hopkins U & Fusion Energy Development LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI Martin Peng SNL UC Davis UC Irvine NSTX Program Director UCLA UCSD Oak Ridge National Laboratory U Maryland U Rochester @ Princeton Plasma Physics Laboratory U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Joint Spherical Torus Workshop and Tsukuba U U Tokyo US-Japan Exchange Meetings (STW2004) JAERI Ioffe Inst TRINITI KBSI 29 th September – 1 st October, 2004 KAIST ENEA, Frascati Kyoto University CEA, Cadarache IPP, Jülich Yoshida-Honmachi, Kyoto, Japan IPP, Garching U Quebec ST2004-9/29-10/1/04 ST Science & Fusion Energy

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 ( κ , δ , A …) 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 ST2004-9/29-10/1/04 ST Science & Fusion Energy

Tokamak Theory in Early 1980’s Showed Maximum Stable β T Increased with Lowered Aspect Ratio (A) • A. Sykes et al. (1983); F. Troyon et al. (1984) on maximum stable toroidal beta β T : β Tmax = C I p / a 〈 B 〉 ≈ 5 C κ / A q j ; 〈 B 〉 ≈ B T at standard A C ≈ constant (~ 3 %m·T/MA) ⇒ β N Plasma Z Cross 〈 B 〉 = volume average B ⇒ B T Section κ = b/a = elongation b a a A = R 0 /a = aspect ratio 0 R q I ≈ average safety factor R 0 I p = toroidal plasma current B T ≈ applied toroidal field at R 0 • Peng & Strickler (1986): What would happen to tokamak as A → 1? − How would β N , κ , q j , change as functions of A ? ST2004-9/29-10/1/04 ST Science & Fusion Energy

ST Plasma Elongates Naturally, Needs Less TF & PF Coil Currents, Increases I p /aB T ⇒ Higher β Tmax Natural Elongation, κ Small Coil Currents/I p (q edge ~2.5) A = 1.5 A = 2.5 I TF / I p κ ≈ 2.0 κ ≈ 1.4 (~aB T / I p ) Z Σ I PF / I p κ 0 R R A ST Tokamak • Naturally increased κ ~ 2; I TF < I p , I PF < I p ⇒ higher I p ; lower device cost • Increased I p /aB T ~ 7 MA/m·T ⇒ β Tmax ~ 20%, if β N ~ 3 • Increased I p q edge /aB T ~ 20 MA/m·T ⇒ improved confinement? ST2004-9/29-10/1/04 ST Science & Fusion Energy

Very Low Aspect Ratio (A) Introduces New Opportunities to Broaden Toroidal Plasma Science How does shape determine pressure? ST Plasmas Extends ST Plasmas Extends • Strong plasma shaping & self fields Toroidal Parameters Toroidal Parameters (vertical elongation ≤ 3, B p /B t ~ 1) • Very high β T (~ 40%), β N & f Bootstrap A = R/a can be ≥ 1.1 How does turbulence enhance transport? • Small plasma size relative to gyro-radius (a/ ρ i ~30–50) • Large plasma flow (M A = V rotation /V A ≤ 0.3) • Large flow shearing rate ( γ ExB ≤ 10 6 /s) How do plasma particles and waves interact? • Supra-Alfvénic fast ions (V fast /V A ~ 4–5) 2 ~ 50) • High dielectric constant ( ε = ω pe 2 / ω ce How do plasmas interact with walls? • Large mirror ratio in edge B field (f T → 1) • Strong field line expansion How to supply mag flux without solenoid? START – UKAEA Fusion • Small magnetic flux content (~ l i R 0 I p ) ST2004-9/29-10/1/04 ST Science & Fusion Energy

ST Research Is Growing Worldwide Concept Exploration (~0.3 MA) Proof of Principle (~MA) Pegasus (US) HIT-II (US) MAST (UK) NSTX (US) Globus-M Pegasus MAST HIT-II Proto-Sphera TS-3,4 START SUNLIST HIT-I NSTX TST-M CDX-U HIST, LATE Rotamak-ST ETE CDX-U (US) Globus-M (RF) ETE (B) TS-3 (J) TS-4 (J) TST-2 (J) SUNIST (PRC) HIST (J) ST2004-9/29-10/1/04 ST Science & Fusion Energy

Pegasus Explores ST Regimes As Aspect Ratio → 1 ST2004-9/29-10/1/04 ST Science & Fusion Energy

NSTX Exceeded Standard Scaling & Reached Higher I p /aB T , Indicating Better Field and Size Utilization • Verified very high beta CTF β requirement well within stability prediction ⇒ new physics: Limits, without using active control 2 ≤ 38% β T = 2 µ 0 〈 p 〉 / B T0 β N = β T / (I p /aB T0 ) ≤ 6.4 DEMO β N = 6 〈β〉 = 2 µ 0 〈 p 〉 / 〈 B 2 〉 ≤ 20% • Obtained nearly sustained plasmas with neutral beam and bootstrap current alone CTF – Basis for neutral beam sustained ST CTF at Q~2 – Relevant to ITER hybrid mode optimization • To produce and study full non- inductive sustained plasmas – Relevant to DEMO Columbia U, LANL, PPPL ST2004-9/29-10/1/04 ST Science & Fusion Energy

Detailed Measurements of Plasma Profiles Allows Physics Analysis and Interpretations Plasma Flow Shearing Rate up to ~10 6 /s ST2004-9/29-10/1/04 ST Science & Fusion Energy

Strong Plasma Flow (M A =V φ /V Alfvén ~0.3) Has Large Effects on Equilibrium and Stability Equilibrium Reconstruction • Internal MHD modes with Flow stops growing pressure surfaces 2 magnetic surfaces • Pressure axis shifts out by ~10% of outer minor radius 1 • Density axis shifts by ~20% Z(m) 107540 0 T e (keV) 1.4 330ms 1.2 1.0 0.8 -1 n e (m -3 ) 0.6 4x10 19 0.4 M A 0.2 0.0 -2 0.4 0.6 0.8 1.0 1.2 1.4 R(m) 0.5 1.0 1.5 2.0 R(m) Columbia U, GA, PPPL, U Rochester ST2004-9/29-10/1/04 ST Science & Fusion Energy

High-Resolution CHERS, SXR, and In-Vessel B R and B P Sensors Reveal Strong Mode-Rotation Interaction In-vessel sensors measure SXR shows rotating 1/1 rotating mode as v φ decays mode during v φ decay before mode locking CHarge-Exchange Recom- bination Spectroscopy (CHERS) shows v φ 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 ST2004-9/29-10/1/04 ST Science & Fusion Energy

Active Control Will Enable Study of Wall Mode Interactions with Error Fields & Rotation at High β T Resistive Wall Mode Growth Rate (s -1 ) Vacuum Vessel Conducting Plates Internal Sensors Columbia U, GA, PPPL ST2004-9/29-10/1/04 ST Science & Fusion Energy

Global and Thermal τ E ’s Compare Favorably with Higher A Database 120 0.10 H-mode x2.5 L-mode <thermal> (ms) 80 x1.5 τ E<mag> [s] 0.05 40 τ E 0 0.00 0 40 80 120 0.00 0.01 0.02 0.03 0.04 0.05 <ITER-H98p(y,2)> (ms) τ E τ E<ITER-97L> [s] • Compare with ITER scaling for total • TRANSP analysis for thermal confinement, including fast ions confinement L-modes have higher non-thermal component and comparable τ E ! Why? Bell, Kaye, PPPL ST2004-9/29-10/1/04 ST Science & Fusion Energy

Ion Internal Transport Barrier in Beam-Heated H-Mode Contrasts Improved Electron Confinement in L-Mode iITB? Kinetic Profile Local Error Sampling Transport Barrier region where χ i ~ χ i NC Regions requiring and improved χ e >> χ i data resolution iITB? Axis Edge But L-mode plasmas show improved electron confinement! Why? L-mode H-mode n e (10 13 /cm 3 ) T e (keV) L-mode Magnetic Axis H-mode Columbia U, Culham, ORNL, PPPL ST2004-9/29-10/1/04 ST Science & Fusion Energy

Transport Analysis of NSTX Plasmas Using TRANSP Confirms This Contrast • χ e >> χ i ~ χ NCLASS in most H-mode • χ e ~ χ i in L-mode • Diagnostic Resolution improvements continue L-mode ST2004-9/29-10/1/04 ST Science & Fusion Energy

Analysis Shows Stability to Modes at Ion Gyro-Scale & Strong Instability at Electron Gyro-Scale (H-Mode) Emissivity (mW/cm 3 ) Core Transport In ion confinement MHD event Physics zone Ne 8,9+ • χ ion ~ χ neoclassical Thermal Conductivity • χ elec >> χ ion Impurity • D imp ~ D neoclassical R (cm) Diffusivity ) s m ( t Micro- • Driven by T and n Ne puff gradients instability iITB? calculations • k θ ρ i < 1 (ion gyro- scale) stable or suppressed by V φ shear • k θ ρ i >> 1 (electron gyro-scale) strongly unstable Cadarache, JHU, PPPL, U. Maryland ST2004-9/29-10/1/04 ST Science & Fusion Energy

A Broad Spectrum of Energetic Particle Driven Modes is Seen on NSTX Do these Alfvén Eigenmodes (AEs) and fish-bones (f.b.s) Interact to expel energetic particles? 108170 1000 FREQUENCY (kHz) CAE/GAE TAE 100 “Fish-Bones” 10 0.1 0.2 0.3 TIME (s) PPPL ST2004-9/29-10/1/04 ST Science & Fusion Energy

TAE’s, “Fish-Bones,” and shot 108530 0.8 Plasma Current (MW) CAE/GAE’s Can Interact to 0.4 4 Pnbi (MW) Expel Energetic Particles 0.0 0 0.0 0.1 0.2 0.3 0.4 1.0 H-alpha (a.u.) (I p = 0.65 MA, P b = 3.6 MW, β T = 10%) Synchronous sudden activities of 0.0 1.0 Neutrons (1014/s) • Edge D α rises; D-D neutron drops • Fish-bone modes rises 0.0 • TAE mode crashes f.b. 10- 40 kHz 10 3 • Separately, asynchronous drops of f.b. 10 2 and CAE modes 10 1 10 2 • So far observed for β T ≤ 10% and I p ≤ rms(B) ~ 10 1 700 kA ⇒ high- β effects? 10 0 CAE 500 - 1500 kHz • NPA measured depletion for 50-80 kV at 10 -1 10 3 higher β T – MHD (m/n=4/2) induced? 10 2 • Nonlinear effects relevant to lower β 10 1 burning plasmas ( ITER ) TAE 70 - 150 kHz 10 0 0.20 0.25 0.30 TIME (s) PPPL ST2004-9/29-10/1/04 ST Science & Fusion Energy