Particle charging in low-pressure plasmas

Particles embedded in a plasma acquire a net charge as a result of collisions with electrons and ions. Due to the stochastic nature of encounters between particle and charged species, the instantaneous charge fluctuates. The static properties of the charge fluctuations are quantified for particles surrounded by an undisturbed plasma in orbital motion limit. For particles that satisfy the condition e²/4πε₀RkT_e≪1 the charge distribution is a Gaussian function whose average and variance is related to the ion and electron currents toward the particle. For a Maxwellian plasma, in particular, analytical solutions are developed for the average charge and the variance as a function of the parameters of the plasma n _e/n_i, T_e/T_i, and M _e/M_i. Finally, the methodology is extended to non-Maxwellian plasmas using the Druyvesteyn as an example.