A Plasma bomb was an explosive device which was used by the Turei and other races to attack and destroy the Vaadwaur, a Delta Quadrant species in 1476.
The explosive capacity a single plasma bomb is unknown but multiple plasma bombs can be very destructive and can render a planet uninhabitable because of the high radiation plasma bombs generate.
In 2376 USS Voyager found the planet of the Vaadwaur and encountered a group of survivors, who survived their planets nuclear winter in stasis units. (VOY:"Dragon's Teeth")