A plasma cannon (also called an electrothermal accelerator) is an experimental projectile weapon, which accelerates a projectile by means of a plasma discharge between electrodes at the rear of the barrel, generating a rapid increase in pressure.
It functions similarly to other types of firearms, except that it uses a plasma discharge instead of a chemical propellant (e.g. black powder or nitrocellulose).
The gap between the electrodes ionizes, turning the non-flammable propellant medium into a super heated conductive plasma.
This makes it possible to "dial-in" any velocity desired and allows the projectile to reach a speed at which it would be possible to "outrun" the burn rate of a conventional propellant.
Even a small plasma cannon with only the firepower of an air gun weighs about 20 kg (44 lb) (without current supply).