GTC Status: Physics Capabilities & Recent Applications Y. Xiao for GTC team UC Irvine

Non-perturbative (full-f) & perturbative (  f) 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 Applications: microturbulence & MHD modes Global Gyrokinetic Toroidal Code (GTC) [Lin et al, Science, 1998] Lin, Holod, Zhang, Xiao, UCI Klasky, ORNL; Ethier, PPPL; Decyk, UCLA; et al

General geometry and profiles General global toroidal magnetic geometry from Grad- Shafranov equilibrium Realistic density and temperature profiles using spline fits of EFIT and TRANSP data No additional equilibrium model is needed Experimental validation GTC poloidal mesh Realistic temperature and density profiles from DIII-D shot # [ Candy and Waltz, PRL 2003 ]

Full-f capability Non-perturbative full-f and perturbative  -f models are implemented in the same version time full-f ITG intensity  f ITG intensity full-f zonal flows  f zonal flows

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 nene  A || ueue figefige nene nini uiui ne1ne1 ue1ue1  ind  es  A || ZF Dynamics Sources Fields

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 >10 5 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]

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  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 CTEM turbulent transport Xiao and Lin PRL 2009 Xiao et al, POP 2010

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

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 Holod & Lin, PoP 2008 Holod & Lin, PPCF 2010