An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating ions using electricity.An ion thruster ionizes a neutral gas by extracting some electrons out of atoms, creating a cloud of positive ions.
These ion thrusters rely mainly on electrostatics as ions are accelerated by the Coulomb force along an electric field.Ion thrusters use beams of ions (electrically charged atoms or molecules) to create thrust in accordance with momentum conservation.//VirtualBrain
The method of accelerating the ions varies, but all designs take advantage of the charge/mass ratio of the ions. This ratio means that relatively small potential differences can create high exhaust velocities. This reduces the amount of reaction mass or propellant required, but increases the amount of specific power required compared to chemical rockets. Ion thrusters are therefore able to achieve high specific impulses.
The drawback of the low thrust is low acceleration because the mass of the electric power unit directly correlates with the amount of power. This low thrust makes ion thrusters unsuited for launching spacecraft into orbit, but effective for in-space propulsion over longer periods of time./via