Global gyrokinetic PIC simulation of Alfven wave, ITG and KBM in GTS*

  We report the recent development in the electromagnetic simulations for general toroidal geometry based on the global particle-in-cell gyrokinetic code GTS. Because of the cancellation problem, the EM gyrokinetic simulation has numerical difficulties in the MHD limit where k_perp ρ_i≈0 and/or β>m_e/m_i. Several approaches have been implemented in the GTS framework to circumvent this problem: (1) p_|| formulation with analytical skin depth term iteratively approximated by simulation particles (Yang Chen), (2) A modified p_|| formulation with ∫E_|| dt used in place of A_||  (Mishichenko). Our simulation shows that both of these approaches successfully mitigate the cancellation problem in the simulation of shear Alfven wave for large aspect ratio geometry. The simulation of electromagnetic ion temperature gradient mode (ITG) and kinetic ballooning mode (KBM) will be presented based on the Cyclone Base Case parameters.