A plasma junction hit by phase cannon fire
A plasma junction or EPS junction was a component of the electro-plasma system on 22nd century Klingon Bird-of-Prey. It was a major flaw in the ship's design, as it was exposed along the nape of the ship's neck and primary hull, vulnerable to enemy fire.
It was also found on NX-class vessels used to tie the electro-plasma system into vital bridge stations. In 2154, Captain Hernandez mentioned to Jonathan Archer that Columbia NX-02 had their science and communications stations linked into the ship's EPS junction, thereby maximizing their effectiveness. (ENT: "Home")
Also in 2154, a stolen Bird-of-Prey under the control of renegade Augments had its entire power grid disabled by a single phase cannon fired by Enterprise NX-01. (ENT: "The Augments")