@makarovAs a science nerd, allow me to interject.
A contained plasma field, aside from eating up an immense amount of power to keep the plasma super-heated (cold plasma is just an ionized gas, and not much use to anyone), would break if exposed to outside electromagnetic fields. Most systems can be rather easily shielded from the disruptive influences of an EMP, but an EMP would most likely cause your plasma to disperse into the air. Furthermore, the blade part of the plasma blade would be quite weak, as you'd need exposed electricity based heating devices along the edge.
Provided the plasma is hot enough, you could cut through pretty much anything. As well as kill people just by holding it close to their face, it should be emitting enough infrared to burn people's skin off at close range. So it's a good thing your char's a vamp, or else the blade would most likely overheat his brain.
So it's pretty damn powerful, but has certain weaknesses.
