Measurement of the Fragmentation Rates of Solvated Ions in Ion Electrospray Thrusters

摘要

Ionic Liquid Ion Sources (ILIS) produce ion beams from ionic liquids and are the basis of ion electrospray propulsion. ILIS beams are typically composed of single ions as well as ion clusters. The ion clusters are metastable and can break up inside the thruster, a phenomena referred to as fragmentation. Fragmentation within the acceleration region of the thruster is detrimental to the propulsive efficiency. Therefore it is imperative to understand the physics behind the fragmentation process. Unfortunately fragmentation is not well characterized and it has been experimentally shown that different ionic liquids produce ILIS beams with different amounts of fragmentation. In this work, the rates at which ion clusters break up were experimentally determined using retarding potential analysis. The beam energy distribution was measured using a retarding potential analyzer placed at several distances from the source. It was found that the rates are likely constant outside of the acceleration region. For a source voltage of 1820 V, the mean lifetime of the lightest ion cluster is approximately 1 µs, which indicates that the solvated species are highly metastable. Improvements to the experimental apparatus and data analysis methods are required to increase the accuracy of the fragmentation rates. In future work, measurements close to the source will be obtained in order to better constrain the fit used to determine the rates.