Plasma Cannon

The Plasma Cannon, also sometimes called the Heavy Plasma Gun, is an Imperial heavy weapon that relies on plasma technology to deliver lethal blasts of superheated matter to the target. Plasma weapons work by using hydrogen fuel suspended in a cryogenic state, in either fuel flasks or backpack containers. As the fuel is fed into the miniature fusion core inside the weapon, the hydrogen energises into plasma which is held in the core of the weapon by powerful electromagnetic containment fields. When fired, the fields dilate open and the plasma is ejected via a linear magnetic accelerator in a bolt of superheated matter akin to a solar flare in appearance and temperature. This bolt will explode on impact and can generate the destructive heat of a small sun. For this reason, Plasma Weapons are sometimes called “sun guns” by the common Imperial population.

Plasma Weapons tax their cooling systems considerably and the Space Marines push the limits of their own resilience by using hydrogen in a higher quantum state in their plasma weaponry than is common in more standard Imperial patterns of the weapons. Plasma Cannons are the largest kind of portable Plasma Weapons, and rather than using the standard fuel flasks that are attached to the weapon, the wielder must wear a large hydrogen fuel canister that can attach to their backpack unit. Plasma Cannons have a greater range and ammunition supply than the standard Plasma Gun, and its violent discharges hurtle like minature suns from its barrel, impacting a large area and producing a significant area of effect. Plasma Cannons also can fire in a maximal mode setting, where the weapon will exhaust even more fuel to provide an even larger blast of plasma on impact, creating a fireball that is capable of destroying heavily-armoured targets. However, like all Imperial Plasma Weapons, Plasma Cannons are prone to overheating and can prove as deadly to the user as to the target.

The Space Marines represent one of the few Imperial infantry units that are capable of carrying Plasma Cannons because of the weapon's heavy weight. A Space Marine's Power Armour also offers better protection against the weapon when it overheats or malfunctions. Plasma Cannons are commonly only wielded by Devastators within Space Marine Chapters, although a member of a Tactical Squad can also carry one. However, Gun Servitors are also capable of carrying Plasma Cannons into battle, and their expendable nature makes them suited to the task of wielding such a dangerous weapon. Plasma Cannons are more commonly mounted on vehicles, however, due to as the effects of overheating are then less severe to the vehicle's crew, who can take refuge within the vehicle's armoured shell. Imperial vehicles such as the many variants of the Leman Russ Battle Tank can mount Plasma Cannons as sponson weapons, while Imperial combat walkers such as Sentinels and Dreadnoughts can also carry Plasma Cannons into battle.

Known Imperial Plasma Cannon Patterns

 * Mark XII Comet Pattern
 * Mark XII Ryza Pattern
 * Mark XIII Pattern
 * M31 Pattern - Ancient pattern of Plasma Cannon still used by the Traitor Legions of Chaos Space Marines

Xenos Plasma Cannons
Analogues of this weapon found in other intelligent races of the galaxy include the Kustom Mega-Blasta of the Orks, the Dark Eldar's Disintegrator and the Eldar Starcannon, which while based on the same technology has a completely different effect on its targets, and suffers no chance of overheating. The Tau also make use of Plasma Cannons which can be mounted on their Hammerhead Gunships.

Change of Terminology
The term "Plasma Cannon" was first used to refer to the weapon during the 3rd Edition release of the Warhammer 40,000 rules set. Prior to the 3rd Edition, the weapons now referred to as Plasma Cannons were called Heavy Plasma Guns.