How does solar electric propulsion (ion propulsion) work?

How fast can the ion engine go?

The ion engine has a small amount of thrust, so it takes a long time to get up to speed. When the ion propulsion system begins operation, DS1 will be in LEO (low Earth orbit) and moving at a slow stately pace (for spacecraft) of about 17,000 mph. The ion engine will then take 15 months and increase the speed of the satellite by 8000 miles per hour. This will top the satellite out at around 25,000 mph after about 15 months.

How does DS1's engine work?
How could something as small as an atom move a space craft?
What is an ion?
How did DS1 get into space?
Could NASA use ion propulsion to put a ship into space?
What is the difference between an ion engine and a conventional one?

How fast do conventional rockets go?
What are the types of rocket propulsion?
What would happen if DS1 ran out of fuel?
Is there any resistance to movement in space for DS1?
What is thrust?

Why do ion engines need a vacuum to work?