Building a Mekanism Fusion Reactor is the ultimate milestone for any technical modded Minecraft player. It transitions your base from standard power grids to massive energy yields, scaling from millions to hundreds of millions of Forge Energy (FE) per tick. Getting it running requires precise multiblock assembly, fuel logistics, and a dedicated ignition sequence.
The core challenge isn't just crafting the blocks—it's managing Deuterium and Tritium supply lines, balancing injection rates, and choosing between air-cooling and water-cooling to prevent your system from stalling.
Multiblock Structure and Assembly Requirements
The reactor forms a 5x5x5 hollow multiblock cube with clipped corners. You'll need specific components crafted from Atomic Alloy, Polonium Pellets, and Steel Casings.
- Reactor Frame: Forms the skeleton of the structure (36+ blocks). The corners must always remain frames, but non-corner faces can swap for glass or ports.
- Reactor Controller: Must be placed on the exact top center block of the structure.
- Reactor Ports: Required for pumping in fuel, water, or extracting energy. You need at least three for a standard setup.
- Laser Focus Matrix: Placed on a face to receive the high-energy laser pulse needed for startup.
The GUI on the Controller will indicate if the multiblock is complete. If it fails to form, double-check that you haven't used reactor glass on the bottom layer or missed a frame block in the corners.
Fuel Production: Deuterium, Tritium, and D-T Fuel
The reactor runs on a mixture of Deuterium and Tritium, which combine to form D-T Fuel. Managing these gases demands dedicated processing machinery.
- Deuterium: Set up an Electrolytic Separator processing heavy water, which is pumped via Electric Pumps equipped with Filter Upgrades.
- Tritium: Route liquid lithium through a Solar Neutron Activator to convert it into Tritium gas.
- D-T Fuel: You can feed the two gases directly into separate ports, or pre-mix them using a Chemical Infuser before pumping the finished fuel into the multiblock.
Pre-mixing allows direct insertion of D-T fuel, bypassing standard injection rate caps if you're chasing extreme endgame power outputs.
The Ignition Sequence
The reactor won't start on its own; it requires a plasma temperature of 100 million Kelvin (100 MK) and a charged Hohlraum placed inside the Controller's inventory slot.
- The Laser Method: Place a Laser Focus Matrix on one of the ports, point a Laser Amplifier at it, and store at least 1 Gigajoule (1 GFE) of energy. Rig the amplifier with a redstone button so you can trigger a single massive pulse.
- The Resistive Heater Method: Alternatively, hook up a Resistive Heater to a reactor port to gradually heat the core. This consumes roughly 18 GFE in total, making it faster if you lack a massive laser setup.
Once the plasma hits 100 MK, the reaction ignites, the internal animation shifts, and power generation begins.
Maximizing Power Output: Air vs. Water Cooling
How you handle heat dictates your energy returns.
- Air-Cooling: The simplest method. Extract energy directly from a port using Universal Cables. At the default minimum injection rate of 2, it outputs 400k FE/t, scaling up to 19.6 million FE/t at an injection rate of 98.
- Water-Cooling: Pipe water into the reactor to convert it into Steam. Route that steam into an Industrial Turbine to generate massive amounts of power. Combined systems running at peak injection rates with turbines can push past 40 million FE/t.
Common Mistakes to Avoid
- Forgetting the Hohlraum: Players often pump in fuel and energy, wondering why the laser won't start the reaction. You must craft a Hohlraum in a Metallurgic Infuser and place it inside the Controller GUI before firing.
- Starving the Fuel Supply: If your injection rate outpaces your pumps and Solar Neutron Activators, the internal tank empties and the reaction shuts down instantly. Build buffer chemical tanks to maintain stable input.
- Incorrect Port Modes: You must configure output ports using a Configurator tool while sneaking to switch them to output mode, otherwise energy or steam won't transfer out.
Frequently Asked Questions
What happens if the fusion reactor runs out of fuel?
The reaction simply stops, the plasma temperature drops below 100 MK, and power generation ceases. It won't explode, but you'll need to use your laser or heater to reignite it once fuel is restored.
Can I change the dimensions of the fusion reactor?
No. Unlike Fission Reactors, the Fusion Reactor is a fixed 5x5x5 multiblock. You cannot build a larger or smaller variant.
How do I automate the Hohlraum requirement?
You can use mechanical pipes, droppers, or pipe systems to insert a filled Hohlraum into the Controller's inventory slot automatically, though standard setups only require one to jump-start the reaction unless it completely runs out of fuel and shuts down.
Why won't my industrial turbine accept steam from the reactor?
Ensure your turbine is large enough to handle the total steam throughput of the reactor, and verify that your pressurized tubes are set to push and pull correctly between the reactor output port and the turbine valve.
