It'll shoot a very thin stream of plasma.
Besides, lightning is plasma -- heating the air to over a million degrees farenheit -- and it doesn't catch "on fire" except in the very immediate vicinity of the bolt. A plasma stream would look just like a straight lightning bolt, more or less.
Wow, good catch though, Ruski... the superheatng of the air around a plasmathrower would cause a crack just like a lightning bolt and smell like ozone!
SWEET! FRICKIN' SWEET!