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GTC Simulation of Turbulent Transport in Fusion Plasmas Zhihong Lin

GTC Simulation of Turbulent Transport in Fusion Plasmas Zhihong Lin University of California, Irvine & US DOE SciDAC GPS (PI, P. H. Diamond) & GSEP (PI: Z. Lin) centers. UCI GPS & GSEP Activities. CTEM turbulence and transport ( Y. Xiao )

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GTC Simulation of Turbulent Transport in Fusion Plasmas Zhihong Lin

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  1. GTC Simulation of Turbulent Transport in Fusion Plasmas Zhihong Lin University of California, Irvine & • US DOE SciDAC GPS (PI, P. H. Diamond) & GSEP (PI: Z. Lin) centers

  2. UCI GPS & GSEP Activities • CTEM turbulence and transport (Y. Xiao) • Momentum transport in ITG & CTEM turbulence (I. Holod) • Energetic particle (EP) transport by ITG turbulence (W. Zhang) • TAE excitation by EP using GTC and HMGC (A. Bierwage) • GTC simulation of ITG gap in reversed shear plasmas (W. Deng) • Prominent gap in linear eigenmode; Gap partially filled by turbulence spreading? • GTC simulation and theory of GAM physics (H. Zhang, F. Liu) • Role of GAM in regulating edge turbulence in HL-2A? • Linear damping and propagation by temperature gradient and electric field shear • Nonlinear harmonics generation • GTC development: integration of key capabilities, e.g, kinetic electrons, electromagnetic turbulence, general geometry etc • Other UCI Ph.D students: P. Porazik, X. Cheng, O. Luk, Z. Duan, Z. Wang • Theory students (supervised by Prof. L. Chen) collaborating with simulation: Z. Guo, Z. Qiu, D. Liu

  3. GTC Status and Plan • Integration of key capabilities in a single GTC version: done • Kinetic electrons via fluid-kinetic hybrid electron model • Electromagnetic solver using PETSc • General geometry MHD equilibrium and plasma profiles using spline • Global field-aligned mesh using magnetic coordinates • Multi-level parallelism using mixed mode of MPI/OpenMP • Advanced I/O using ADIOS • Plan for GTC upgrades: full-f ion simulation & neoclassical physics • GTC is part of benchmark suites for DOE OASCR, NERSC, and Cray; pioneering applications of ORNL LCF computers; INCITE (30M hours); SciDAC GPS, GSEP, & CPES • Key active developers: Z. Lin, I. Holod, W. Zhang, Y. Xiao (UCI), S. Klasky (ORNL), S. Ethier (PPPL). Supported by SciDAC GPS, GSEP, & CPES

  4. Electromagnetic GTC via Fluid-Kinetic Electron dne dge1&dfi dA|| Dynamics due dA|| ZF dfes dfind Fields dA|| dui dne1 dni due1 dne Sources

  5. Wave-particle decorelation in ETG Turbulence • Validity of quasilinear theory (QLT) for turbulent transport in toroidal plasmas? ETG, CTEM, ITG • tauto >> 1/g >>twp ~ 1/Dk||ve • Wave-particledecorrelation of parallel resonance d(w-k||v||) dominates • Quasilinear calculation of ce agrees well with simulation • Saturation: wave-wave coupling determines fluctuation intensity • Transport: wave-particle decorrelation determines transport level [Lin et al, PRL 2007]

  6. Saturation and transport in CTEM turbulence • Electron heat transport is important for burning plasma • Collisionless trapped electron mode (CTEM) is a prominent candidate for electron anomalous transport in tokamak core plasma • What is saturation mechanism in CTEM? • What is transport mechanism in CTEM? • Does any transport scaling law exist in CTEM? • Global gyrokinetic particle simulation (GTC) is applied to address these key issues Lin, et al Science, 1998 R₀/LTe=6.9, R₀/LTi=2.2 R₀/Ln=2.2, Te/Ti=1 mi/me=1837, q=1.4, s=0.78 15 Billion particles 29,000 procs for 42 hours Rewoldt/Lin/Idomura CPC 2007 CTEM

  7. Zonal Flow Effect in CTEM turbulence • Radial streamers break and merge: dynamic system • When removing the zonal flow: • Strong radial streamer forms • Transport level increases about 5 times • Zonal flow is the dominant saturation mechanism for CTEM

  8. CTEM Characteristic Time Scales • CTEM Instability is kinetic --- driven by toroidal precessional resonance • Given turbulence intensity, e heat transport can be understood as a fluid process due to weak detuning of precessional resonance • In ITG, kinetic and fluid processes can both regulate turbulence [Lin et al, PRL2007

  9. Transport in CTEM turbulence • χi: diffusive, proportional to local EXB intensity • χe: track global profile of intensity; but contain nondiffusive, ballistic features ITG: Lin PRL 2002

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