Finite-β simulation of microinstabilities

Edward A. Startsev, Wei-li Lee

Abstract: A new split-weight perturbative particle simulation scheme for finite-β plasmas in the presence of background inhomogeneities is presented. The scheme is an improvement over the original split-weight scheme, which splits the perturbed particle response into adiabatic and non-adiabatic parts to improve numerical properties. In the new scheme, by further separating out the adiabatic response of the particles associated with the quasi-static bending of the magnetic field lines in the presence of background inhomogeneities of the plasma, we are able to demonstrate the finite-β stabilization of drift waves and ion temperature gradient modes using a simple gyrokinetic particle code based on realistic fusion plasma parameters. However, for βmi/me ≫ 1, it becomes necessary to use the electron skin-depth as the grid size of the simulation to achieve accuracy in solving the resulting equations, unless special numerical arrangement is made for the cancelling of the two large terms on the either side of the governing equation. The proposed scheme is most suitable for studying shear-Alfvén physics in general geometry using straight field line coordinates for microturbulence and magnetic reconnection problems.