An actual ion cannon would be nothing like the ion cannons from Star Wars. I'm pretty sure Lucas used that name just because it sounded cool. A flintlock pistol would be easily more efficient than whatever an ion cannon would be. Ions are simply charged particles of matter. This most often takes place in acids and bases with the H+ and then something like Cl-. Technically, if you're drinking lemonade, orange juice, coffee or sports drinks with electrolytes, you are drinking ions. Conventional batteries today such as the mercuric or lithium ion batteries, they're nothing special; it's a cannon that fires globs of chemicals. I don't see exactly how this could even be close to efficient. The other possibility is that the cannon fires ionizing radiation. In this case the cannon would most likely melt itself and irradiate the craft and the area around it. The beam itself would not carry ANY explosive power at all.
