Old guides below.

Fusion V6

The quick guide to make fusion in version 6 is:

Mix at least 250 mols of ~~CO2~~ H2, at least 250 mols of plasma and a "good amount" of tritium. Then heat it all to over 10000K.
Many gases have a "fusion power" stat that may affect a fusion reaction when present. You can find this stat by looking directly in the "code".

For a more detailed description of how fusion works and what you can create with it, you may need to try to understand the pull request that last changed it (as of April 2020) combined with the "original pull request", or find other sources.

Fusion V5

Fusion occurs when you give plasma and tritium a lot of heat energy. It'll quickly convert all of the gases to an extremely hot mixture based on the power of the reacting mixture. This power can be increased or decreased depending on what exactly is in the mix. The ratio of plasma is kept at exactly half of the mix for higher power and the rest of the gas, the mediation gas, should have a high fusion power and a low average specific heat.

Gas fusion power: Each gas has a different amount of power it can contribute to the fusion process per mole, typically the rarer it is the stronger it will be. If it isnt listed here, it doesn't provide any power to the equation but can still be used to lower the average heat capacity or required temperature.

Gas	Fusion power
CO2	1.25
Water Vapor	8
Nitryl	16
BZ	8
Stimulum	7
Pluxonium	10

Power ratio formula: When fusion occurs and plasma is exactly half of the mix, the following formula is used to find the tier of the fusion:

If plasma is not half of the mix, it will begin a bell curve decay in the power ratio.

Required Temperature: 3e9 joules must exist in the mix for the fusion to occur

Power tier Depending on the power you create from the mixture, fusion can go into 4 different tiers scaling to have typically higher rarity in produced gas, energy produced, and dangerous side effects such as radiation bolts, lingering radiation, tesla shocks, and an explosion. A portion of the gas is converted to raw energy, growing depending on tier.

Low tier:
- 0-5 power ratio
- Low chance of explosion and short range shock
- Produces 10% BZ and 90% CO2 with a high enough heat to make a tiny amount of hyper noblium

Medium tier:
- 5-20 power ratio
- Moderate chance of explosion and medium range shock
- Produces 25% Nitryl and 75% N2O with a high enough heat to make several hyper noblium bombs

High tier:
- 20-50 power ratio
- High chance of explosion and wide range shock
- Produces 1/12th Stimulum and 11/12th pluxonium with a large amount of heat

Super tier:
- 50+ power ratio
- 100% chance of explosion and very wide range shock
- Produces 100% Tritium with a massive amount of heat

Example Since fusion tends to be a little difficult for people to find entry to, a sample for doing so will be provided here.

mix: 5000 moles of trit, 5000 moles of plasma.
Average mediation specific heat: 10
Average mediation fusion power: 1
Mediation mole count: 5000
Fusion power:(5000*1)/(10*80) = 6.25 = medium tier
Required heat: (3e9)/((average specific heat)(total moles)) = 2857.14 k

Tips for working with fusion:

at the highest efficiency roughly 30% of the gas you use will be lost to the pump to the canister and to the heat exchanger to the can so prepare accordingly.
Work with friends. It has high setup and maintenance requirements, and your fellow atmos techs, engineers and toxins scientists are all valuable resources in your pursuit of very hot things.
Although some gases may have high fusion power they might have too high specific heats to give you the tier you want, as a rule of thumb Stimulum, Nitryl, and BZ are all very useful for reaching higher tiers of fusion.
Fusion requires Heat energy not Temperature meaning the more moles you can fit into an area, the lower the temp is for you to start fusion.
It is recommended to have a sacrificial lamb preform the finale in an unused area such as space, if not be wearing radiation protection and have an excuse for the gods you are about to anger.
It is intended to preform fusion in a canister but doing it in a pipe net or incinerator is possible.
Heat exchanges are your friend for starting your reaction. Connect it to tritium burn chamber or canister to get the heat needed to start it.
Typically gases with high power but also high specific heats like water vapor or pluxonium will become exponentially more efficient the more you use due to the average specific heat increasing less and less the more you use.
Should you want to release a canister that you used for fusion in a room full of people, consider shooting it to break it open so you arent right next to it.

Beyond the basics:

You can harness the radiation produced from fusion to produce power using rad collectors. Earn your keep as a member of engineering. Or just use it for pluoxium production.
The higher the temperature, the prettier the fire. See if you can get the prettiest color fire.
Traitors can harness fusion reactions to devastating results if done correctly.