Fully implicit particle-in-cell simulation of gyrokinetic electromagnetic modes in XGC1 without the cancellation issue*

Electromagnetic gyrokinetic simulation of tokamak plasma has been suffering from the so-called “cancellation problem,” in which the long wavelength modes make the simulation blow up. Recently, a fully implicit electromagnetic Vlasov-Darwin particle-in-cell algorithm using fluid preconditioner is developed [1]. We adopt this scheme to XGC1, a 5D total-f gyrokinetic code.  For the parallel velocity, v_|| is used instead of the canonical momentum p_||. Picard iteration is used with fluid pre-conditioner. Subcycling of particle motions and fixed-point accelerator raise the simulation efficiency. The cancellation problem does not appear even in the longest wavelength Alfven wave range (n=0, m=1) at tokamak plasma β_e values. Kinetic ballooning and micro-tearing modes will be discussed for NSTX and other tokamak plasmas.

 [1] G. Chen, L. Chacon, Comput. Phy. Comm. 185, 2391 (2014)