How does solar electric propulsion (ion propulsion) work?

How are atoms charged?

A charged atom has either too many or too few electrons. In DS1, atoms are heated until they are very high energy and unstable. The are then hit by electrons that are discharged by a cathode ray in the thruster chamber. When the electrons hit the atoms in the chamber, they cause some of the electrons in the atoms to be stripped or knocked away. The mass of superheated, charged atoms with disassociated electrons becomes a plasma.

When one or more electrons is knocked off of an atom, it becomes positively charged. It is now an positive ion. A negative ion can be made by adding an electron to an atom.

What is an atom?
What is an ion?
How does DS1's engine work?

What does electrically charged mean?
What is a cathode?
What is plasma?
What's an electron?

What else uses plasma?