Plasma is actually a different type of matter. Matter exists in four states: solid, liquid, gas. Plasma is the fourth state. But plasma weapons are not mass driver weapons, not in the way we're using them. Early attempts at creating plasma weapons would have certainly placed them into the mass driver category. Plasma, unlike lasers, have significant mass. The damage from plasma is from heat damage, not kinetic energy transferral. The funny thing about our plasma weapons is that they really are fancier lasers. The plasma is encased in an immensely powerful energy field that ensures that the plasma is transferred nearly instantly (i.e., near light speed) to the intended target. The laser field helps keep the plasma from behaving like a gas. The net result is that a ship hit with a plasma based weapon will first have its hull damaged or ruptured through the plasma and then by the energy field around it damaging vital internal elements of the enemy ship.