  The spatial and orientational distribution in a dilute active suspension of
non-Brownian run-and-tumble spherical swimmers confined between two planar hard
walls is calculated theoretically. Using a kinetic model based on coupled
bulk/surface probability density functions, we demonstrate the existence of a
concentration wall boundary layer with thickness scaling with the run length,
the absence of polarization throughout the channel, and the presence of sharp
discontinuities in the bulk orientation distribution in the neighborhood of
orientations parallel to the wall in the near-wall region. Our model is also
applied to calculate the swim pressure in the system, which approaches the
previously proposed ideal-gas behavior in wide channels but is found to
decrease in narrow channels as a result of confinement. Monte-Carlo simulations
are also performed for validation and show excellent quantitative agreement
with our theoretical predictions.
