A hydrodynamic model is used to investigate the characteristics of positive ions in the sheath region of a low-pressure magnetized electronegative discharge.Positive ions are modeled as a cold fluid,while the electron and negative ion density distributions obey the Boltzmann distribution with two different temperatures.By taking into account the ion-neutral collision effect in the sheath region and assuming that the momentum transfer cross section has a power law dependence on the velocity of positive ions,the sheath formation criterion(modified Bohm’s criterion)is derived and it is shown that there are specified maximum and minimum limits for the ion Mach number M.Considering these two limits of M,the behaviors of electrostatic potential,charged particle density distributions and positive ion velocities in the sheath region are studied for different values of ion-neutral collision frequency.
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