I've worked on a document for the Fusion Cannon Man Portable since T4 came out. I don't take credit for this except maybe the settings. Most of it was from T4 Emperor's Arsenal and MegaTraveller, if I remember right. But it's not canon. Er... But it is a Cannon.
FUSION CANNON–MAN PORTABLE (FC-MP)
The Imperial designated weapon fS1055 is a fearsome weapon. Common military slang uses the Second Imperium abbreviation style – FCMP (or sometimes FGMP, MPFC, or more informally BFG). Increases in power storage technology combined with known advances in material science and increased efficiency contra-grav allows a self-contained weapon with its own recoil compensation, motion stabilizers and side-blast reduction, allowing use by unaugmented troops. High-energy weapons, such as these, fire bolts of super-heated fusing plasma at their targets and cause damage by their intense heat and kinetic energy. Exact details are unavailable from the manufacturer for security reasons, but unclassified records and photographs of the units allow reasonable estimates of the technology involved.
In the case of the fS1055 weapon unit, hydrogen is stored in a cartridge that can hold 1 kilogram (1000 grams) of hydrogen. The cartridge is loaded into the weapon in a detachable cylindrical magazine. These cartridges are easily replaceable in the field, taking only 1 round to do so. Each Fusion Gunner in a platoon would usually carry one extra cartridge, allowing a firing of 2000 rounds on the lowest setting.
The hydrogen is fed into an ignition chamber (at a maximum rate of 10 grams per round), which has a metastable magnetic containment field. The fusion power pack powers an eximer laser igniter, through a high-density superconducting cable, to heat the hydrogen to a point where it reaches an excited super-hot state of matter known as plasma. A second eximer laser excites the plasma past this state to a point where the hydrogen plasma begins to fuse into helium. Current technologies allow for an energy density sufficient to realize higher fusion temperatures (in excess of 1 million degrees).
When it reaches maximum energy, the fusing plasma then moves through the plasma shunt to a flux aperture. When the aperture opens, the fusing hydrogen is then released through a magnetically focused field along the weapon's barrel, which is maintained at near vacuum by electrostatic fields, so the magnetic field can accelerate the Fusion Bolt to incredible speeds (in excess of 8600 meters per second). The high initial velocity Fusion Bolt is approximately 1cm in diameter per gram of hydrogen used, but it begins to dissipate immediately.
Part of the energy of the explosively expanding Fusion Bolt is bled off to pump a homopolar generator, which in turn powers a "pilot" laser. The pilot laser vaporizes a tunnel through the atmosphere through which the Fusion Bolt is discharged. (without the pilot laser the Fusion Bolt dissipates far too quickly.)
When the ball-shaped Fusion Bolt strikes an object, after a lightning-like flash along the projectile's path, and a large thunderclap a fraction of a second later, the velocity-based kinetic energy of the fusing hydrogen plasma combines with its extremely high temperature to blast a hole in the target, and incidentally spray white-hot plasma and fragments of the target in all directions.
Plasma splatter has a primary burst radius of .5 meters per gram of hydrogen expended. All characters within the primary and secondary burst radii are subject to hits by fragments of plasma, including the target. Plasma fragments are the equivalent of white phosphorus fragments for damage purposes (1d4 for every gram of hydrogen).
If the intended target doesn’t expend more than half of the energy from the Fusion Bolt through damage when hit (i.e. a Fusion Bolt inflicts 108 points this round, but the target has less than 54 points total), the target experiences blow-through. The Fusion Bolt creates a hole in the target and continues on to strike objects or people behind the original target at half damage. If the target does expend more than half of the Fusion Bolt’s energy, and the target is reduced to 0 points, the target is vaporized and there is no blow-through.
Due to the heaviness of the weapon and the energies involved, a compensator package is used. A gravity field generator is included to allow the weapon to move weightless, a gyroscopic inertial compensator to negate recoil, and an energy dampener around the muzzle to reduce the possibility of flash-burns. The weapon's computer system automatically biases the field to provide near total recoil compensation.
The power pack has sufficient energy to allow 10 days of continuous use before recharging is necessary. A quick-shot capacitor holds the energy to heat up to 10 grams of hydrogen, allowing the fusion pack to be turned off when the weapon is stored. The fusion pack is automatically started when the gun is fired, and takes one round to “warm up”. Recharging the power pack takes approximately 2 hours from a starship or similar power reactor.
The FCMP has six firing settings (only one can be used per round – it takes one round to change to a new setting), which can be used in a multitude of environments.
• On Setting A, a single Fusion Bolt is fired using only one gram of hydrogen (Damage 1d6+6).
• Firing Setting B allows a burst of 10 Fusion Bolts and uses one gram of hydrogen per Bolt (Damage 1d6+6 per Bolt).
• Setting C fires a burst of 3 Fusion Bolts and uses 3 grams of hydrogen per Bolt (Damage 3d6+18 per Bolt).
• Setting D sends 2 Fusion Bolts flying and uses 5 grams of hydrogen for each Bolt (Damage 5d6+30 per Bolt).
• Setting E fires one Fusion Bolt using 10 grams of hydrogen (Damage 10d6+60).
• The final Setting X is a weapon of last resort. It is a timed detonation of the weapon. On a 60 second duration, the weapon expends all remaining fuel and overloads the fusion power pack. It produces grenade damage of 10d6 (x50) points in a 50-meter blast radius. This setting cannot be used if less than 100 grams of fuel are left.
The fS1055 has a computer link data socket, which can be used to augment the targeting of the weapon. When used in conjunction with Battle Dress, the computer link engages the combat armor’s helmet-mounted holographic heads-up display and projects crosshairs on the faceplate for targeting, which activates the armor’s computer-assisted threat analysis program that highlights targets by their appraised level of lethality. (+2 to hit) The weapon may be fired every combat round. It can also be mounted on a tripod for better efficiency. (+1 to hit)
