Precursor Solitons in Plasma Flow Past Charged Obstacles: Role of Obstacle Bias and Ion Temperature Anisotropy

We investigate electrostatic ion-acoustic precursor solitons in a plasma flow past an absorbing charged obstacle using two-dimensional (2D) electrostatic PIC simulations. A key outcome of the present formulation is that ion-temperature anisotropy can enable precursor formation even in regimes where isotropic plasmas, due to Landau damping, cannot sustain such structures. Specifically, temperature anisotropy in the 2D drifting flow along the x-direction, arising from a reduction in the transverse thermal velocity (y-direction) relative to the parallel thermal velocity (x-direction), favors the generation of coherent upstream structures whose effectiveness increases with stronger anisotropy. Both positive and negative obstacle polarities are considered to identify the conditions for upstream nonlinear structure formation. A negatively biased plate produces only a wake-like response, whereas a positively biased plate generates upstream density pulses. This study offers physical insight into nonlinear wave formation in streaming plasmas over charged objects and could be useful for plasma-based debris detection in the low Earth orbit (LEO) region.