Case studies of ion focusing in the downstream region of a modeled low Earth orbit spacecraft

The effect of plasma and charged particle interaction with spacecraft in a low Earth orbit (LEO) environment leads to ion focusing and the formation of an ion void in the downstream region as a result of charging. Simulations and investigations using a fixed potential imposed on the spacecraft showed the nonsignificance of geophysical parameter changes to ion focusing. Variation of the temperature ratio (T_r) contributed only to local ion focusing and manifested as two-ion streamers dispersed at the upper and lower edges of the spacecraft—the outermost layers of the satellite structure at the top and bottom, respectively. A simulation involving changing the ambient plasma density (N_p) also showed the formation of local ion focusing, in which ions were more concentrated as the density increased. Furthermore, auroral electron density (N_ae) variation had no clear impact on ion focusing, as indicated by static two-ion structures in the wake field. However, variation of the object potential (ϕ) strongly affected ion focusing formation, leading to distortion of the initial ion void region behind the spacecraft. The formation of ion focusing in this study was subject to the electric field produced by the object potential and the ambipolar electric field resulting from plasma expansion in the downstream region.