How does solar electric propulsion (ion propulsion) work?

What is a cathode and why do we need one?

A cathode is a metal electrode. It is negatively charged, which means the metal making it up has more electrons than protons or neutrons. A cathode can serve as a source for free electrons for this reason. These electrons repel each other, and can shoot away from the cathode.

We need two cathodes in the ion propulsion system in DS1. The first one provides the electrons that bombard the atoms in the plasma chamber and help make them into positive ions. The second one releases electrons into space to neutralize the ions that shoot out into space and propel DS1 forward.

How does DS1's engine work?
What is an ion?
What happens to the ions once they leave the space craft?
What are other ion using technologies?

What is plasma?
What causes ions to leave DS1?
What does electrically charged mean?
How are atoms charged?
What's an electron?