MOLECULAR DYNAMICS SIMULATION OF LIQUID GALLIUM ELECTROSPRAY THRUSTERS

Open Access
Author:
Kim, DaeYong
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Michael Matthew Micci, Thesis Advisor
Keywords:
  • electrospray
  • molecular dynamics simulation
  • liquid gallium
  • electric field
Abstract:
In this thesis, a 3-D molecular dynamics (MD) simulation of an electrospray thruster was developed. This electrostatic thruster is operated by an electric field generated by an extraction ring at a negative potential and uses liquid gallium as the propellant and platinum as the tube wall. The aim of this project is to make a simulation of an electrostatic thruster operating in a cone-jet mode over a short operating time and to characterize the performance of the electrostatic thruster in a number of variations in operation conditions. We have first approached this project to model liquid gallium at 320K as the propellant. To this end, we used a molecular dynamics simulation in small scale which has 40,896 gallium atoms, integrating via the Lennard-Jones 12-6 potential. The platinum capillary tube was modeled by platinum atoms located at fixed metal lattice sites. The potential between gallium atoms and platinum atoms was approximately modeled based on the Lennard-Jones 12-6 as well. We solved Poisson’s equation for electric potential and electric field between the capillary and the downstream extraction ring with and without the presence of space charge and the equation of motion for a set of gallium ions. In our simulations we made the assumption that since liquid gallium and platinum are perfect conduction materials, there is no the electric field in the platinum capillary and that the space between the two electrodes is a vacuum where the relative dielectric constant is zero. MD simulation allowed us to show the formation of the liquid gallium Taylor cone around the tip of the platinum capillary and the motion of gallium ions and ion clusters. The results of molecular dynamics simulations present the total current and the average velocity of gallium ions passing through the extraction ring versus variations of operation conditions such as the separation between the two electrodes, the operation voltage and the inner radius of the extraction ring.