Experimental investigation of precursor solitons in a flowing plasma*

Over the past decade, theoretical studies by Sen et al. [1] have proposed that when a charged object moves through a plasma at a speed larger than the ion acoustic speed, it generates ion acoustic solitons. The solitons are excited in front of the moving object and propagate faster than the object. This novel effect has possible application in tracking small sized space debris in the Earth’s ionosphere. To explore this application, Truitt and Hartzell [2] investigated the excitation of precursor soliton for the plasma conditions expected in low Earth orbit (LEO), i.e. 200-1000 Km. The first experimental demonstration of the generation of a precursor soliton in a flowing dusty plasma over a charged object was reported by Jaiswal et al. [3]. Recently, Kumar et al. [4] demonstrated the excitation of two and three-dimensional precursor solitons in a flowing dusty plasma.  In this work, we report experimental studies looking for precursor solitons in a flowing plasma. The experiments are performed in the Space Plasma Simulation Chamber (SPSC) at the Naval Research Laboratory (NRL). A series of biased rings placed at the end of the SPSC are used to create a radial electric field along with an applied axial magnetic field resulting in an azimuthal plasma flow. The inferred flow speed (assuming the driven flow is the E x B speed) changes from a subsonic to a supersonic value by different combinations of radial electric fields and axial magnetic fields. A debris object is placed in the chamber such that plasma flows past over it. The debris is biased with a square voltage pulse.