Orbiting ions in the Debye shielding cloud around dust particles in weakly collisional plasmas

Inside the plasma sheath of a negatively charged dust grain, ions lose energy in occasional collisions with neutrals. Thus, trapped ions with negative energy may be created that contribute to the electrostatic shielding of the dust´s charge. A kinetic model is solved for the fraction of the trapped ions in the Debye cloud as a function of dust size. The relative number of trapped ions in the Debye cloud reaches a maximum at dust size a/λ_D≈0.3(T_e/T_i)^-0.6, where λ_D is the Debye length and T_e and T_i are the electron and ion temperatures, respectively. More than 50% of Debye shielding may be due to ions that are trapped.