Orbital debris-generated ion acoustic solitons in isothermal magnetized plasma

The generation mechanism for ion acoustic solitons due to speeding orbital debris in warm isothermal ionospheric plasma with the background magnetic field oriented at an arbitrary angle to the debris trajectory is analyzed. It is found that the fluctuations in the floating potential, which the debris acquires due to charging, can be amplified into growing ion acoustic waves by plasma streaming onto the debris. Normally, the ion acoustic fluctuations are ion Landau damped in the ionosphere because their phase speed matches the acoustic speed for equal ion and electron temperatures. However, in the debris frame, the plasma streams with an inhomogeneous velocity profile. The velocity shear in the streaming ions can overcome Landau damping by effectively increasing the wave phase speed by a factor proportional to the product of the shear and the wave normal angle, causing the Landau resonance to match the velocities of the tail of the distribution rather than the core. Consequently, the fluctuations can grow to sufficiently large amplitudes even in an isothermal plasma and trigger nonlinear effects resulting in ion acoustic solitons. For debris motion at an angle to the magnetic field, unique signatures are generated by the combination of coherent and incoherent processes—both along and across the magnetic field directions. These may be exploited for distinguishing between debris-generated soliton signatures and those arising due to natural causes and thereby facilitate positive identification of the orbital debris.