Metal ion thruster using magnetron electron-beam bombardment (MIT-MEB)

A new concept of ion thrusters, metal ion thrusters using magnetron electron-beam bombardment (MIT-MEB) is demonstrated. Ion thrusters provide thrusts via electrostatic fields to accelerate ions. They are widely used in spacecrafts due to the high exhaust speed. Although the thrust is very little, the final velocity of the spacecraft is much higher than using traditional rockets. For propellant, inert gases are used in conventional ion thrusters. Contrarily, a metal propellant is used in MIT-MEB. The metal propellant is solid-state, high density, easy to store, and cheap. The size of the ion thrusters can be reduced dramatically. Therefore, they can be used in a small spacecraft for both attitude and orbit control, deep space exploration, and low earth orbit. The concept of electron-beam physical vapor deposition (EB-PVD) is used to generate metal ions. A metal target is bombarded and thus heated and evaporated. An electric potential accelerates thermal-emitted electrons, which ionize the metal vapor via electron-impacting ionization. The magnetic field of a permanent magnet is used to guide the accelerated electrons towards the center of the target. This increases the efficiency of the process. Particularly but not necessarily, zinc is used for propellant due to its higher vapor pressure compared with other metals at the same temperature. This means that a lower temperature is required for zinc to be vaporized. To demonstrate our concept, an ion thruster of 10.3 ± 0.7 μ N with a power of 26.2 ± 0.7 W was constructed as a prototype. Its mass is less than 500 g, and its diameter is $\sim 50mm$. The accelerating electric potential is 1 kV. Although an optimized design was not developed yet, we demonstrated the feasibility of building metal ion thrusters for the first time. It is a new design space and unexplored method of using a metal propellant. (paper)