We have simulated plasma flow along the divergent magnetic field of an electron cyclotron resonance (ECR) microwave plasma source stream. We assume that ions undergo charge exchange and elastic scattering collisions with the neutral gas in the downstream region. A Monte Carlo description for the ion dynamics, coupled with Boltzmann electrons, is used to develop an iterative scheme for solution of the Boltzmann equation and quasineutrality. We have studied the effect of the magnetic field and neutral gas pressure on the plasma and floating potentials, and on the ion energy incident on the sample.