| Summary: | The wake behind a spherical particle smaller than the Debye length ( De) in
owing
plasma is calculated using a particle-in-cell code. The results with di erent magnitudes
of charge reveal substantial non-linear e ects down to values that for a
oating particle
would correspond to a particle radius approximately 102 De. The peak potential in
the oscillatory wake structure is strongly suppressed by non-linearity, never exceeding
approximately 0:4 times the unperturbed ion energy. By contrast, the density peak
arising from ion focusing can be many times the ambient. Strong heating of the ions
occurs in the non-linear regime. Direct ion absorption by the particle is not important
for the far wake unless the radius exceeds 101 De, and is therefore never signi cant (for
the far wake) in the linear regime. Reasonable agreement with full-scale linear-response
calculations are obtained in the linear regime. The wake wavelength is con rmed and an
explanation, in terms of the conical potential structure, is proposed for experimentally-
observed oblique alignment of di erent-sized grains.
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