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GTC Status: Physics Capabilities & Recent Applications Y. Xiao for GTC team UC Irvine Global Gyrokinetic Toroidal Code (GTC) • Non-perturbative (full-f) & perturbative (df) simulation • General geometry using EFIT & TRANSP data • Kinetic electrons & electromagnetic simulation • Neoclassical effects using Fokker-Planck collision operators conserving energy & momentum • Equilibrium radial electric field, toroidal & poloidal rotations; Multiple ion species • Parallelization >100,000 cores • Global field-aligned mesh • Parallel solver PETSc • Advanced I/O ADIOS [Lin et al, Science, 1998] Lin, Holod, Zhang, Xiao, UCI Klasky, ORNL; Ethier, PPPL; Decyk, UCLA; et al • Applications: microturbulence & MHD modes General geometry and profiles • General global toroidal magnetic geometry from GradShafranov equilibrium • Realistic density and temperature profiles using spline fits of EFIT and TRANSP data • No additional equilibrium model is needed • Experimental validation Realistic temperature and density profiles from DIII-D shot #101391 [Candy and Waltz, PRL 2003] GTC poloidal mesh Full-f capability • Non-perturbative full-f and perturbative d-f models are implemented in the same version full-f ITG intensity df ITG intensity full-f zonal flows df zonal flows time Kinetic electrons • Hybrid fluid-kinetic electron model is used • In the lowest order of electron-to-ion mass ratio expansion electrons are adiabatic: fluid equations • Higher-order kinetic correction is calculated by solving drift-kinetic equation Electromagnetic capabilities • Only perpendicular perturbation of magnetic field considered • Parallel electric field expressed in terms of effective potential, obtained from electron density • Continuity equation for adiabatic electron density, corrected by drift kinetic equation. • Inverse Ampere’s law for electron current • Time evolution for parallel vector potential • Gyrokinetic Poisson equation for electrostatic potential Structure of GTC algorithm Dynamics dne dfi&dge dA|| Fields due dA|| ZF dfes dfind Sources dA|| dui dni dne1 due1 dne Equilibrium flows and neoclassical effects • Equilibrium toroidal rotation is implemented • Radial electric field satisfies radial force balance • Neoclassical poloidal rotation satisfies parallel force balance • Fokker-Planck collision operator conserving energy and momentum Multiple ion species • Fast ions treated the same way as thermal ion specie • Energetic ion density and current non-perturbatively enter Poisson equation an Ampere’s law Numerical efficiency • • • • Effective parallelization >105 cores Global field-aligned mesh Parallel PETSc solver Advanced I/O system ADIOS Recent GTC applications • Electrostatic, kinetic electron applications – CTEM turbulent transport [Xiao et al, PRL2009; PoP2010] – Momentum transport [Holod & Lin, PoP2008; PPCF2010] – Energetic particle transport by microturbulence [W. Zhang et al, PRL2008; PoP2010] – Turbulent transport in reversed magnetic shear plasmas [Deng & Lin, PoP2009] – GAM physics [[H. Zhang et al,NF2009; PoP2010] • Electromagnetic applications – Electromagnetic turbulence with kinetic electrons [Nishimura et al, CiCP2009] – TAE [Nishimura, PoP2009; W. Zhang et al, in preparation] – RSAE [Deng et al, PoP2010, submitted] – BAE [H. Zhang et al, in preparation] CTEM turbulent transport The CTEM turbulent transport studies reveal • Transport scaling---Bohm to gyroBohm with system size increasing • Turbulence properties---microscopic eddies mixed with mesoscale eddies • Zonal flow---Zonal flow is important for the parameter applied • Transport mechanism Xiao and Lin PRL 2009 Xiao et al, POP 2010 electrons: track global profile of turbulent intensity; but contain a nondiffusive, ballistic component on mesoscale. The electron transport in CTEM is a 1D fluid process (radial) due to lack of parallel decorrelation and toroidal precession decorrelation and weak toroidal precession detuning ions: diffusive, proportional to local EXB intensity. The ions decorrelate with turbulence in the parallel direction within one flux surface Experimental validation • Real radial temperature and density profiles are loaded • Zonal flow solver is redesigned for the general geometry • Heat conductivity uses the ITER convention • The measured heat conductivity (preliminary) is close to Candy Waltz 2003 value q 2 T Toroidal momentum transport • Simulations of toroidal angular momentum transport in ITG and CTEM turbulence • Separation of momentum flux components. Non-diffusive momentum flux • Intrinsic Prandtl number Pr 0.2 0.7 (ITG) Pr 0.5(CTEM) Holod & Lin, PoP 2008 Holod & Lin, PPCF 2010