Destablilized ion sound oscillations in Hall plasma devices for electric propulsion

It is shown that current closure in the chamber walls destabilizes ion acoustic waves in Hall plasmas with ${\mathbf E} \times {\mathbf B}$ electron drift. Such unstable modes may enhance both near-wall conductivity and turbulent electron transport in Hall thrusters for electric propulsion. It is shown that the instability is sensitive to the wall material: the wall with very high dielectric permittivity (such as metal wall) reduces the mode growth rate by an order of magnitude but does not eliminate the instability completely.