  Ionic liquid ion sources are a promising technology that can be used for many
applications from space propulsion to focused ion beam microetching. Ionic
liquid ion sources produce ion beams by extracting single ions and metastable
solvated ion clusters from the surface of the ionic liquid and accelerating
them using an electric field generated by applying a voltage between a sharp
tip and a plate with an aperture. The solvated ion clusters often fragment in
the electric field region, reducing the specific impulse and efficiency for
propulsion applications and increasing the beam spot size for focused ion beam
applications.
  Fragmentation behavior has previously been characterized in the region with
no electric field. However, fragmentation in an electric field has not been
investigated as experimental results are difficult to interpret. The goal of
this work is to use various numerical methods to characterize fragmentation
under the effect of an electric field. Molecular dynamics simulations are
performed of various ionic liquid clusters under different conditions to
determine the rate of fragmentation. Physics-based models are compared to the
molecular dynamics results with the goal of deriving a new model that accounts
for the effect of the electric field on fragmentation. Approximate Bayesian
computational methods are employed to infer the temperature of different ionic
liquid cluster types and the percentage of the beam composed of each species by
comparing simulated retarding potential analysis curves to experimental ones.
Finally, the results of multi-scale N-body simulations are postprocessed and
compared to experimental data. Results show agreement between experimental data
and N-body simulations using the fragmentation rates determined by molecular
dynamics.

Chemical Physics