No abstract

In order to better evaluate the trade-offs between different simulation options for an electrospray thruster plume, we have developed a multi-scale n-body code to compute the evolution of a single emitter electrospray plume in the pure ionic regime. The electrostatic force computations in the simulation are captured through the use of three different computational algorithms with various degrees of approximation. The results of the simulations for a simple test case are compared in terms of computational speed and accuracy. The test case utilizes a single operating point (323nA) for a stable meniscus solution for the ionic liquid EMI-BF4 firing in the positive pure ion mode. Complex species and probabilistic fragmentation processes are neglected. An overview is provided of the trade-off between accuracy and computational speed for the three algorithms in the context of simulating the electrostatic interactions between particles. For a large number of particles, the faster algorithms show a significant reduction in computational time while maintaining a high level of accuracy with a proper choice of tuning parameters.

The angular distribution of emitted species in electrospray ion beams is not well characterized and can have negative effects on propulsive performance and emitter lifetime. We present an experimental characterization of the angular distribution of emitted species in a single electrospray ion beam as a function of firing voltage using time of flight mass spectrometry. Angular current distributions indicate the central axis of emission varies up to 10 • from the central axis of the emitter tip. Variation in the ion species as a function of angle depends on the firing voltage. Simulations of single particle trajectories indicate that fragmentation of ion clusters results in ion products moving closer to the center of the beam and neutral products spreading up to 47 • depending on how rapid fragmentation occurs. Experimental results are compared to multiscale full-beam simulations of electrospray emission and future use of these simulations to explain angular beam behavior is discussed.