While not always used to power a Warp Drive, a Warp Core is needed to power such a device.
A matter-Antimatter reactor, it is vastly superior to Nuclear Generators and even fusion reactors. In the amount of energy it produces. It is not often used due to the sensitive controls needed to control the reaction which require Power Control Crystals to create the control matrix needed to maintain the reactions.
The destruction of a Warp Core would destroy an entire ship, maybe even a fleet if it is running at max capacity.
Warp Core generally appear as large light emitting columns with bases with numerous terminals and or connected to a larger complex.