Features of emissive cathode microturbulence

Cathode emitters, used to sustain plasma thruster ionization and neutralization, have been the subject of modeling and optimization studies for several decades. Though apparently simple in operation, they exhibit poorly-understood mode transitions and features such as ion acoustic turbulence [1, 2], implicated in the production of high-energy ions that lead to erosion. Gaining insight into the nature of these and other unstable modes present in both thrusters and cathodes can advance predictive discharge modeling capabilities. In recent coherent Thomson scattering studies of cathode emitters, we have identified and characterized a millimeter-scale unstable mode present in the plume of a cathode operated with a Hall thruster. The mode propagation within the region connecting cathode and thruster plumes is found to exhibit a directivity influenced by the thruster magnetic field. Spatial localization of this mode is also determined. Results from these investigations provide new information on the coupling dynamics of the cathode and thruster plumes.

[1] B. A. Jorns, I. G. Mikellides and D. M. Goebel, Phys. Rev. E 90, 063106 (2014)

[2] K. Hara and C. Treece, Plasma Sources Sci. Technol. 28, 055013 (2019)