I always thought of them as a large plasma torch in a magnetic bottle. You probably could eventually make a device like that. Not really a practical weapon though.
From Wikipedia:
Plasma is an effective means of cutting thin and thick materials alike. Hand held torches can usually cut up to 2 in (48 mm) thick steel plate, and stronger computer-controlled torches can pierce and cut steel up to 12 inches (300 mm) thick. Formerly, plasma cutters could only work on conductive materials, however new technologies allow the plasma ignition arc to be enclosed within the nozzle thus allowing the cutter to be used for non-conductive workpieces.
Since plasma cutters produce a very hot and very localized 'cone' to cut with, they are extremely useful for cutting sheet metal in curved or angled shapes.
Of course those machines are rather large.
Esenstially, thats what people are thinking will eventually be our lightssabers...thing is that in the starwars universe, the lightsaber is a "laser sword" so..yeah..
Crenshaw