Collisional Effects on Nonlinear Ion Drag Force for Small Grains

Abstract

The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

Fig 1. corrected in this version

References in corpus (4)

• On the Wake Structure in Streaming Complex Plasmas
• Intergrain forces in low Mach-number plasma wakes
• Fully self-consistent ion-drag force calculations for dust in collisional plasmas with external electric field
• Dressed test particles, oscillation centres and pseudo-orbits

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• Wakes in inhomogeneous plasmas
• Collision induced amplification of wakes in streaming plasmas
• Plasma flow around and charge distribution of a dust cluster in a rf discharge
• Wake effects of a stationary charged grain in streaming magnetized ions
• Accurate momentum transfer cross section for the attractive Yukawa potential
• Theory of a cavity around a large floating sphere in complex (dusty) plasma
• Transverse magnetic field influence on wakefield in complex plasmas
• Dim and bright void regimes in capacitively-coupled RF complex plasmas
• Variational approach to Yukawa fluids. I. Thermodynamics