Weakly charged round micro-plasma jet flows into vacuum

This paper presents a model for highly dilute microplasma jet flows expanding into a vacuum from a round exit, with given number density, bulk velocity, temperature, and potential at the exit. The Debye length at the exit is assumed to be large, the quasi-neutral condition is adopted to treat charges, and the potential field is computed with the Boltzmann relation. At farfield, the exit degenerates as a point source, and simplified analytical formulas for the density, velocity, temperatures, potential, and electric field components are obtained. From the crucial centerline properties, exact but more compact solutions are further developed. The treatment is based on the gas kinetic theory, and the results are analytical and generic. The results include rich physics and offer insights into better understanding of many existing models in the literature, for example, the cosine law plume model shall be used with caution. The current results can be widely applicable to estimate the whole flow and potential fields, with reduced simulation and measurement costs. Farfield property estimations can be performed without numerical simulations and measurements. Based on these results from this work, more advanced models may be further developed.