Global gyrokinetic simulation of ion temperature gradient driven turbulence in plasmas with canonical Maxwellian distribution

A global gyrokinetic toroidal particle code for a 3D nonlinear simulation (GT3D) has been developed to study the ion temperature gradient driven-trapped electron mode (ITG-TEM) turbulence in reactor relevant tokamak parameters [1]. In GT3D, gyrokinetic ions and drift-kinetic (trapped) electrons are solved using a finite-element PIC method. The code uses a new δf method based on a canonical Maxwellian distribution F CM (P φ ,ε,µ), which is defined by three constants of motion in the axisymmetric toroidal system, the canonical angular momentum P φ , the energy ε, and the magnetic moment µ. A quasi-ballooning field solver enables linear and nonlinear high-m,n global calculations with a good numerical convergence. Conservation properties are improved by using the optimized particle loading. The code has been optimized for massively parallel scalar and vector machines, and it operates with a high processing efficiency and scalability on the JAERI Origin3800 system and on the Earth Simulator. From comprehensive linear global analyses over a wide spectrum (n=0~100) in reactor relevant tokamak parameters (a/ρ ti =320~460), it is found that the reversed shear configuration produces an effective stabilizing effect on the ITG mode in the q min region through global effects [1]. In the preliminary linear calculations with drift-kinetic (trapped) electrons, it is confirmed that the ITG-TEM mode spectrum obtained from GT3D qualitatively agree with the former results obtained using a global gyrokinetic spectral code. In the nonlinear calculations of the ITG turbulence with the Cyclone base case parameters [2], it is found that the new method based on F CM can simulate a zonal flow damping correctly, and that zonal flow oscillations, which often grow rapidly in a conventional code based on a local Maxwellian distribution F LM (Ψ,ε,µ), do not appear in the nonlinear regime [1]. Through linear zonal flow damping tests [3], spurious driving effects on zonal flows in the conventional code with F LM are identified.