Why ion propulsion?
There are not many technologies which use free ions in vacuum: the most common use outside of spacecraft is in ion implantation processes which computer chip makers use when they are making your computer chips. However, several household devices use the other part of the atom---the electron.
The screen on your computer and your TV both work by bombarding the screen with electrons. The electrons are pumped out of a cathode ray tube in the back of the computer and sweep the screen from left to right in rows going down the page, like your eyes sweep a page you read, except that the electron sweep happens thousands of times a second. When the electrons hit the screen they cause the atoms in the screen to absorb energy and then give it off again. As they give off the energy, they start to glow. These thousands and millions of different colored glowing things are what make up the picture on your screen.
What is an atom?
What is an ion?
What is the difference between an ion engine and a conventional one?
How does solar electric propulsion (ion propulsion) work?
What does electrically charged mean?
How are atoms charged?
What is a cathode?
What's an electron?