Two-Dimensional Ion Acoustic Turbulence in the Hollow Cathode Plume of a Hall Effect Thruster*

Ion acoustic turbulence is known to exist is the plume of hollow cathodes. This turbulence is thought to dominate the plasmadynamics of the region. The instability grows through inverse electron Landau damping and is damped by ion Landau damping and ion-neutral collisions. Previous works have confirmed their existence in the plume of stand-alone hollow cathodes as well as cathodes operating in a thruster system, and derived a self-consistent fluid model for wave energy transport. The models suggest that these waves can propagate oblique to the geometry. However, previous measurements in the cathode-thruster plume only determined their properties in the axial direction. Therefore, the goal of this work is to investigate multi-axis ion acoustic turbulence wave measurements in the plume of a cathode-thruster system. Propagation direction through the plume is investigated through two-dimensional measurements. Finally, the impact of neutral density on the damping of the wave and its impact on the dynamics of the region is experimentally characterized.