Catherine Miller

Research Summary:

The relationship between the performance of iEPS thrusters and the composition of the ionic liquid propellant is not well understood. There are hundreds of ionic liquids commercially available and perhaps millions that could be synthesized in the future. Approximately ten ionic liquids have been tested in iEPS thrusters and each liquid shows a different level of performance. This variation is due to differences in the mass and energy spectra of the ionic liquid ion source (ILIS) ion beams that are created. The ion beams consist of single ions as well as ion clusters, which are metastable and break apart during the acceleration phase within the thruster. Each ionic liquid shows a different amount of clustering and cluster break up, also called fragmentation. There is little theoretical understanding of the relationship between liquid composition and performance, which motivates experimental investigation. In this work, a specialized instrumentation suite has been designed and built in-house to characterize ILIS ion beams with unprecedented detail. A high resolution time of flight (TOF) detector is used to measure the mass spectra of the ion beam and obtain the amount of fragmentation that occurs within the acceleration region. A spherical retarding potential analyzer (RPA) is used to measure high resolution energy spectra of the full ion beam to obtain the amounts of fragmentation and the rates at which ion clusters break apart. By characterizing many ionic liquids spanning a wide range of liquid properties, the relationship between liquid composition and iEPS performance can be uncovered. The ultimate goal of this research is to be able to estimate the relative performance of untested ionic liquids based on their properties alone.