  Nonintrusive measurements of plasma properties are essential to evaluate, and
numerically simulate, the in-flight performance of electric propulsion systems.
As a logical first step in the development of new diagnostic techniques, this
work depicts the implementation of multiphoton ionization and coherent
microwave scattering (MPI-CMS) in a gridded-ion accelerator operating on rare
gases. Presented studies primarily comprise photoionization spectroscopy of
ground and excited state-populations of both neutrals and ions supplemented by
optical emission spectroscopy and Langmuir probe derived plume properties.
Results suggest the potential of MPI-CMS for non-intrusive measurements of
specie number densities.
