The Dawn spacecraft combines innovative state-of-the-art technologies pioneered by other recent missions with off-the-shelf components and, in some cases, spare parts and instrumentation left over from previous missions.
With its wide solar arrays extended, Dawn is 19.7 meters long. The ion thruster is powered by large solar panels. The power ionizes the fuel (Xenon) and then accelerates it with an electric field between two grids. Electrons are injected into the beam after acceleration to maintain a neutral plasma.
Ion Engines are the most exciting new rocket propulsion system since the Chinese invented the rocket about a thousand years ago. Most rocket engines use chemical reactions for power. They combine various gases and liquids to form explosions which push the rocket through space. Chemical rocket engines tend to be powerful but have a short lifetime.
Ion propulsion gets its push from electric fields instead of chemical reactions. Its forces are gentler, but they are so efficient, a mission can last for years before running out of fuel.
https://dawn.jpl.nasa.gov