The fusion reactor of the Emissary is an immensely intricate fusion power plant, constructed by the AXIOM Corporation to harness the power of stars and generate enough energy to power a starship and its FTL drive.
The Emissary is powered, at its core, by a magnetized target fusion (MTF) reactor producing up to 10 gigawatts of energy, an output capable of powering over 900,000 homes. Utilizing an intake-compression-exhaust stroke, Emissary's reactor works by compressing deuterium-tritium plasma, enriched from hydrogen, into an extremely small space using extremely powerful magnets. The compression action drastically increases the density and temperature of the plasma, forcing it into a critical volume where it undergoes fusion. Tritium atoms combine in the confined area to produce tremendous energy and extremely high-pressure helium gas, which is diverted out of the reactor during the exhaust stroke to thrusters, where it is used as propellant.
Terminology
The operation of a reactor utilizes several key words as part of its terminology.
- D: Deuterium. An uncommon, stable isotope of hydrogen with 1 neutron in addition to the proton and electron pair found in baseline hydrogen (protium). Deuterium is regularly extracted from seawater on Earth, Europa, and Enceladus, and additionally siphoned from Jupiter's atmosphere.
- T: Tritium. A radioactive isotope of hydrogen with 2 neutrons. Extremely rare in nature and can typically only be synthesized by neutron reactions of metals such as lithium.
- D-T (deetee): Deuterium-tritium fusion fuel. Mixed in various ratios (typically 1:1 to 2:1 deuterium-tritium) and injected into fusion reactors as fuel.
- Lith: Shorthand for lithium orthosilicate (Li4SiO4). Lith is a white, brittle ceramic material composed of lithium atoms bonded to orthosilicate. During fusion, they can be used either as part of a breeding blanket (in tokamak-type reactors) or as pellets (in MTF-type reactors) to produce additional tritium and neutrons from the lithium inside.
- Molsaphene: An advanced hot, viscous coolant consisting of graphene nanoparticles suspended in lithium fluoride and beryllium fluoride (FLiBe). Its 'cold' state is around 500 degrees Celsius, but is far cooler than the 10,000+ degrees inside of fusion reactors, and has an extremely high thermal coefficient. As a result, it can quickly and effectively wick heat away from the reactor to prevent the interior from melting.
- HfCN: Hafnium carbonitride. A ceramic with an extremely high melting point that makes it an ideal lining for fusion reactors.
Components
Fuel
The reactor's fuel typically consists of deuterium and tritium (D-T) gas mixed in a 2:1 ratio. Deuterium is typically the primary fuel stored in the ship, with sufficient pressurized supply to last up to 720 days without replenishment. Fuel stores are topped off on every visit to a spaceport. Tritium, in a lesser capacity, can also be filled at spaceports, but due to its rarity must be supplemented by internal synthesis via the N-alpha (n, α) reaction.
Tritium production via lithium
The Emissary, in addition to its hydrogen storage, also comes stocked with hundreds of tonnes of lithium orthosilicate (Li4SiO4), or lith, typically pressed into 5mm spherical pellets, that are used for tritium production. During reactor operation, the lith pellets can be injected into the reactor along with the hydrogen gas for fusion. During the compression stage, the temperature in the reactor chamber becomes high enough for the lith to vaporize. This disperses throughout the fusion chamber, where the lithium inside the pellets reacts with the excess neutrons produced during fusion to create additional alpha radiation as well as tritium atoms. The resultant tritium is used to boost the reaction even more, resulting in higher output while consuming less stored fuel.
Coolant
The Emissary utilizes a nanofluid suspension of graphene particles immersed in a solution of lithium fluoride and beryllium fluoride (FLiBe) molten salt for its coolant, referred to as a molten salt-graphene (molsaphene) coolant. Molsaphene has an extremely high thermal conductivity, high specific heat, and low vapour pressure, allowing it to be circulated throughout the ship's coolant piping without risking vaporization, boiling, or cavitation in circulation pumps.
Molsaphene is exposed to the vacuum of space via an array of radiators that actively work to disperse as much heat into space as possible via radiation.
Reactor lining
To withstand the extreme temperatures brought about by the fusion reactor, the reactor chamber is lined with tungsten plates coated in a 10mm layer of hafnium carbonitride (HfCN) ceramic and actively cooled with molsaphene coolant. The HfCN-coated tungsten has an extremely high melting point and is capable of withstanding fusion reactions without being structurally compromised.
Energy capture
The heat energy and neutron radiation emitted by the fusion in the reactor is captured by an array of inductive magnetic converters, otherwise known as the IMC array. During the expansion stroke, the expanding plasma of charged particles and fusion products carries high levels of electrical charge, and it 'pushes' against an induced magnetic field in the reactor. This creates a voltage differential that results in the energy being harvested by the converters and converted into electricity. Up to 73% of the energy released by a fusion reactor can be directly harnessed into electricity; this amount can be varied depending on thruster power, as the more energy is used for electricity, the lower the thrust output of the engines.
Operation
The reactor consists of "strokes", similar to a combustion engine, in which fuel is injected into the reactor (intake), compressed (compression), undergoes fusion (ignition), expands outward (expansion), and is vented (exhaust). The process typically happens at a rate of around 60-120 strokes per minute (1-2 per second) depending on output needed.
- During the intake stroke, fuel plasma is injected into the reactor along with several lith pellets; the amount is dependent on the desired output and power level of the reactor.
- During the compression stroke, the plasma compresses and heats up, vaporizing the lith and releasing lithium.
- The fusion stroke is the critical threshold where fusion begins almost immediately. As the hydrogen fuel fuses into helium, enormous amounts of alpha radiation and neutrons are released.
- The expansion stroke is when the plasma expands outward after compression, and its energy is captured by the IMC array.
- The exhaust stroke moves the high-pressure, high-temperature plasma out of the reactor chamber and into thrusters, where it is accelerated by a series of magnetic coils and propelled outward.