Antimatter reactor
From Memory Alpha, the free Star Trek reference
An antimatter reactor was a power generation device that utilized antimatter. Antimatter reactors typically emitted neutrinos as a byproduct.
In 2151, Subcommander T'Pol detected neutrino emissions from a city on the Akaali homeworld despite the society being pre-industrial. The neutrinos were later found to be caused by a Malurian antimatter reactor that was powering a secret underground veridium mining operation. (ENT: "Civilization")
