Ion-Kinetic Calculations of the Collisional Kelvin-Helmholtz Instability

Using a recently implemented hybrid (kinetic ion/fluid electron) algorithm in the LANL particle-in-cell code VPIC [1], we study Kelvin-Helmholtz (KH) unstable sheared flow layers including full ion kinetics. The ion-ion collisions are treated with the Takizuka-Abe [2] particle-pairing algorithm, which includes the velocity dependence of the screened Coulomb collisions. In agreement with fluid predictions [3], the KH instability is suppressed by ion viscosity for Reynold’s numbers below ~100, corresponding to Knudsen numbers greater than ~0.01 for subsonic flows. In addition to resolving the physical collisional viscosity, the particle treatment allows us to track plasma particle mixing over time. [1] K. J. Bowers, et al., Physics of Plasmas, 15, 055703 (2008). [2] T. Takizuka & H. Abe, Journal of computational physics 25, 205-219 (1977). [3] E. Roediger et al., Monthly Notices of the Royal Astronomical Society, 436, 1721-1740 (2013).