Study of Electron Trajectories in Metal Ion Thruster using Magnetron E-beam Bombardment (MIT-MEB)

Abstract

The Metal Ion Thruster using Magnetron E-beam Bombardment (MIT-MEB) which uses the principle of electron-beam (E-beam) evaporation was developed in our group In this thesis we studied electron behaviors in both experiments and simulations There are three parts in the MIT-MEB: a metal evaporator an ion accelerator and a neutralizer Electrons emitted by the heated filament of the E-gun are accelerated toward the target made of Zinc by the electric field provided by an accelerating voltage V_{{ m acc}} A magnet is placed behind the target so that electrons follow the magnetic field lines and reach the center of the target The target is heated and evaporated when electrons bombard on it When the metal vapor is impacted by electrons emitted from the thermal filament part of the vapor is ionized Ions are then accelerated by the applied electric field providing thrusts Electrons from the neutralizer would leave the thruster with ions and keep the thruster in neutral Therefore electron trajectories play an important role in MIT-MEB We did a series of experiments with V_{{ m acc}} equal to 500 750 and 1000 V We found that fewer electrons reach the target in lower V_{{ m acc}} than that in higher V_{{ m acc}} in experiments We suspected that the electric force would accelerate electrons toward the target while the magnetic-mirror force would reflect electrons back to the filament of the E-gun preventing them to reach the target More electrons might be returned in lower V_{{ m acc}} than that in higher V_{{ m acc}} Therefore we studied electron trajectories in simulations However in simulations no electrons were reflected by the magnetic mirror force once there was an electric force from V_{{ m acc}} greater than 1 V It coincided with a simple analytic model where V_{{ m acc}}geqq0 13 V was sufficient to accelerate electrons overcoming the magnetic-mirror effect So we have rolled out the magnetic-mirror effect in the MIT-MEB Nevertheless we can move the filament of the E-gun sideway In this case the component of the electric field parallel to the magnetic-mirror force much smaller than the magnetic-mirror force will potentially reduce Thus electrons may be reflected by the magnetic-mirror force Therefore using other simulations which could simulate the thermionic electron emission and changing the design of the MIT-MEB need to be conducted as future work

Date of Award	2020
Original language	English
Supervisor	Po-Yu Chang (Supervisor)