Overtaking collisions of double layers and solitons: Tripolar structures and dynamical polarity switches

Overtaking collisions between double layers and solitons are investigated through the numerical simulation of the Gardner equation that governs small-amplitude double layers. The results show that the double layer emerges unaffected after the completion of the collision. However, the soliton that emerges from the collision has the opposite polarity of the soliton prior to the collision. In addition, it is shown that a transient tripolar electric field structure forms during the collision. Possible applications to spacecraft observation of electrostatic solitary waves are briefly discussed.