Investigation Of Double Layer In The Far Wake Region Of Space Vehicles And The Downward Current Region Of Aurora

Double layer is a local structure in the plasma capable of sustaining high potential drops. Typically, they are quoted as having a width of tens of Debye lengths (the correlation length for potential fluctuations in a plasma). Al'pert et al. showed that double layer is formed in the wake region of space vehicles moving through ionosphere. Studying this structure is important for detecting a space vehicle with a stealth characteristic and preventing space vehicles being harmed by double layer. Besides, the measurements by the FAST(Fast Auroral SnapshoT) satellite reveal double layers which can be possible mechanism of accelerating electrons also exist in the downward current region of the aurora.First, on the basis of the non-steady non-linear coupling equations of low-frequency potential, high-frequency field and density disturbance in the far wake region of space vehicles by Li et al., we have numerically solved the coupling equations, and obtained the evolution of low-frequency potential. The results show that double layer is formed in the far wake region of space vehicles. The combined effects of the collapse density arising from the collapse field and the interaction of the vehicle with plasmas lead to the formation of the double layer. The ramp potential and thickness of the double layer that we obtain are tens of kTi/ei and tens of Debye lengths respectively, which are in agreement with the previous calculated results by Al'pert et al.Second, on the basis of the nonlinear coupling equations of low-frequency potential, high-frequency field and density disturbance in strong turbulent plasmas, we have numerically calculated the nonlinear coupling equations. The evolution of low-frequency potential is obtained. The results show that double layer in the downward current region of the aurora is formed by localized drop in density owing to collapsed high frequency field. The structure is a double-double layer and a nonlinear entity—caviton. And the ramp potential of the double layer is in range of 14-40V and the thickness of the structure is between 100 and 200m, roughly tens of Debye lengths, which are all in harmony with the measurements by FAST satellite.