Simulating positively charged magnetospheric spacecraft and quasi-neutral plume mitigation

In preparation for a future high power magnetospheric mission, simulations and ground experiments have been performed to study the mitigation of spacecraft charging behavior in tenuous plasmas. The proposed mission involves... [ view full abstract ]

In preparation for a future high power magnetospheric mission, simulations and ground experiments have been performed to study the mitigation of spacecraft charging behavior in tenuous plasmas. The proposed mission involves firing a high power electron beam towards the Earth to understand the connections between phenomena in the Earth’s magnetosphere and ionosphere. However, emitting a negatively charged beam in the magnetosphere will induce a positive charge buildup on the spacecraft preventing the beam from reaching its destination.

In this work, the results of simulations and on ground experiments in support of this experiment will be discussed. Curvilinear particle-in-cell (PIC) simulations suggest that the positive charge buildup can be neutralized by emitting a dense plasma from a hollow cathode. The principle mechanism for charge mitigation requires ion emission from the quasi-neutral surface that is governed by the Child Langmuir law [1,2].

Experiments performed at the Plasmadynamics and Electric Propulsion Laboratory (PEPL) focused on validating the ion emission model and key parameters of these simulations. An isolated hollow cathode, simulating the spacecraft, was charged to various positive potentials to study the plasma’s steady state responses. Results demonstrate that the plasma potential and the plasma potential drop across the plasma increases with the changes in spacecraft potential [3] producing an increase in ion drift velocity as the potential drop across the plume also increases. However, this increase is likely anisotropic due to the initial beam-like nature of the emitted plasma. Current work focuses on accurately measuring changes in plume size with spacecraft potential but preliminary analyses suggest the sheath at the walls increases with spacecraft potential.

References

[1] G.L. Delzanno, J.E. Borovsky, M.F. Thomsen, J.D. Moulton, E.A. MacDonald (2015), Future beam experiments in the magnetosphere with plasma contactors: how do we get the charge off the spacecraft?, J. Geophys. Res., 120, 3647–3664, doi:10.1002/2014JA020608. Journal of Geophysical Research, 2015.

[2] G.L. Delzanno, J.E. Borovsky, M.F. Thomsen, J.D. Moulton (2015), Future beam experiments in the magnetosphere with plasma contactors: the electron collection and ion emission routes., J. Geophys. Res., 120, 3647–3664, doi:10.1002/2014JA020608. Journal of Geophysical Research, 2015. 

[3] Leon, O., Miars, G., Gilchrist, B., Delzanno, G. L., and Borovsky, J., “Plasma Plume Behavior in the Presence of Biased Spacecraft,” SCTC 2016.