  A new one-dimensional fluid model for ions in weakly-ionized plasma is
proposed. The model differs from the existing ones in two aspects. First, a
more accurate approximation of the collision terms in the fluid equations is
suggested. For this purpose, the results obtained using the Monte-Carlo kinetic
model of the ion swarm experiments are considered. Second, the ion energy
equation is taken into account. The fluid equations are closed using a simple
model of the ion velocity distribution function. The accuracy of the fluid
model is examined by comparing with the results of particle-in-cell/Monte Carlo
simulations. In particular, several test problems are considered using a
parallel plate model of the capacitively coupled radio-frequency discharge. It
is shown that the results obtained using the proposed fluid model are in good
agreement with those obtained from the simulations over a wide range of
discharge conditions. An approximation of the ion velocity distribution
function for the problem under consideration is also discussed.
