title: Intergrain forces in low-Mach-number plasma wakes.
abstract: Large-scale particle-in-cell calculations of the plasma wake interactions of two negatively charged grains smaller than the Debye length are carried out using the coptic code over a wide range of subsonic plasma flow velocities. In plasmas with the temperature ratio T(e)/T(i)=100, it is found that a single grain's oscillatory wake disappears for flow Mach numbers M less than approximately 0.3, which is the parameter regime where Landau damping is expected to be strong. Neutral collisions suppress potential oscillations above M=0.3, but not the trailing attractive potential peak caused by ion focusing. The transverse (grain-aligning) force on a downstream particle in the wake of another is obtained rigorously from the code in three-dimensional simulations. It shows general agreement with the force that would be deduced from the single-grain wake potential gradient. Except for relatively large grains in the nonlinear collisional regime, the grain-aligning force is very small for slow flow.
authors.affiliation: Plasma Science and Fusion Center and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: I H
authors.initials: IH
authors.lastname: Hutchinson
mesh_terms: D003198:Computer Simulation; D008956:Models, Chemical; D058626:Plasma Gases / Q000737:chemistry*; D012212:Rheology / Q000379:methods*; D014783:Viscosity
chemical_list: D058626:Plasma Gases