  We developed an implicit Particle-in-cell/Monte Carlo model in
two-dimensional and axisymmetric geometry for the simulations of the
radio-frequency discharges, by introducing several numerical schemes which
include variable weights, multigrid field solver, etc. Compared to the standard
explicit models, we found that the computational efficiency is significantly
increased and the accuracy is still kept. Numerical schemes are discussed and
benchmark results are shown. The code can be used to simulate practical
reactors.
