Plasma Troopers are only vulnerable to Plasma Beam attacks. However, since the Plasma Beam is Samus's most powerful weapon, they are the most easily dispatched out of all the Beam Troopers. Use the B button to dodge their attacks and circle around them while quickly pumping them full of Plasma, using crates and pillars for cover. Compared to firing rapidly, the Flamethrower is redundant due to its limited range.