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//spl lambda//sub D//spl ap/0.3(T/sub e//T/sub i/)/sup -0.6/, where /spl lambda//sub D/ is the Debye length and T/sub e/ and T/sub i/ are the electron and ion temperatures, respectively. More than 50% of Debye shielding may be due to ions that are trapped.