What is the name of the final upgrade for Samus's beam in Metroid Prime?

The Plasma Beam is the final standard beam upgrade for Samus in Metroid Prime. She finds it in the Plasma Processing chamber of Magmoor Caverns, after using the Spider Ball and Spider Track to reach the elevated area.

The weapon fires a short-range stream of intense heat. It is especially effective against ice-based enemies and can melt red doors and other heat-sensitive obstacles. Its charged shot deals heavy damage and can ignite certain enemies, making it one of Samus’s strongest conventional weapons for the late game.

The Plasma Beam is often confused with the Phazon Beam. The Phazon Beam is obtained with the Phazon Suit after defeating the Omega Pirate, but it is not a normal selectable weapon upgrade: Samus can use it only in the final battle, when she stands in pools of concentrated Phazon. For ordinary exploration and combat, Plasma Beam is the last of the game’s four selectable beams.

Power Beam, Wave Beam, and Ice Beam are earlier beam systems. Their ammunition-free design also distinguishes them from missile-based Beam Combos such as the Flamethrower.