Not everyone has a chance to visit a Federation Starship. So I thought I would give a brief description of how they generate and use energy. Naturally, this is just a brief description. If you are interested in learning more detail, you would do well to peruse the many official Federation Documents available on the web,
The energy that powers a typical starship is created by a standard matter-antimatter reaction. The reactants in this case are deuterium and anti-deuterium, used due to their ability to supply the large amounts of power needed by warp drive, energy weapons, and the various structural fields. The reaction takes place in a reactor vessel (the warp core) where the fusion reaction is contained by powerful magnetic containment fields. The deuterium is contained in a large tank inside the vessel.. Bussard collectors mounted on the warp coil nacelles are used to collect a small amount of replenishment deuterium as well as hydrogen from space via the ram effect. Although important for other ships functions (see maneuvering thrusters) This is not sufficient to completely replace the deuterium that is consumed. For this reason a Federation starship has to be refueled approximately once every three to five years, depending on class.
The Anti-deuterium is an isotope of hydrogen which contains one antiproton and one antineutron in its nucleus, and one positron orbiting the nucleus. It is manufactured onboard in a catalytic fuel reactor from hydrogen, and then stored in special anti-matter pods. These pods can be ejected from the ship in times of emergency. The pods have a magnetic containment system to contain the anti-deuterium. Normally this system is powered from the primary EPS, but each pod has a small self contained power generator that can also maintain the containment, even if the pod is ejected, or if all other ships power fails.
An important element of the matter-antimatter reactor are the di-lithium crystals used to control and moderate the reaction. Without these the reaction would rapidly get out of control. Di-lithium is used for it’s ability to absorb the anti-deuterium protons while withstanding the immense heat of the plasma. They operate in much the same way that graphite is used to moderate the nuclear fission reactors we all learned about in grade school. As an aside, anyone who has assembled a fission reactor knows very well the necessity of these moderating elements. Some have found out the hard way – to the great dismay of their parents, and the insurance company.
The resulting plasma from the matter-antimatter reaction is distributed to various other parts of the ship through plasma conduits. These conduits also use magnetic containment to direct the plasma flow. The largest of these, known as Jeffries tubes, are used to transfer the large amount of plasma needed, and it’s concurrent energy, into the warp nacelles. From those, the plasma is metered into the actual warp coils via the Gravimetric Field Displacement Manifolds. These serve as the controlling element to control the size and shape of the warp field that is generated. I will not get into the mechanics of the warp drive itself. For most readers, the basics of warp propulsion have already been well covered in their secondary schooling.
Smaller, but still fairly large, plasma conduits supply power to the transporter, the primary structural integrity field generators, and to the weapons bays for use by the phasor emitters. Two completely separate plasma conduits (one for backup) are used to power the primary deflector field emitter dish at the front of the ship. As you are well aware, this is a critical component when travelling at warp speeds, so the backup conduit is not an option. A further large plasma conduit system is used to supply energy to the gravimetric field generators. These coils are used to supply artificial gravity throughout the vessel, and are strategically located near the lower surfaces (as defined by the primary 3-dimensional co-ordinates) of all the primary hull structures.
Smaller plasma conduits, known as EPS (Electro-Plasma System) conduits, run throughout the ship distributing energy to where it is needed for things such as lighting and electronics power, replicators, waste management, water, and environmental systems These conduits are arranged in a tree fashion, called the power transfer grid, and are controlled and monitored at various points by Jamieson power junctions.
A note: There is some controversy over application of the EPS terminology. In older starships the entire power conduit system was known as the EPS system. These older vessels used a relatively few amount of plasma conduits, and powered the major systems (except the warp drive) via standard electrical distribution and EPS power taps.
However, this discussion centers on newer designs where there are separate conduits for the major elements as noted above, and for general ships power, which is now generally called the EPS. Modern starships distribute plasma to many more points than older models there.
At points where normal electrical power is necessary, EPS Power taps, similar to the seebeck devices used in your own home, are installed. These are used to convert the heat from the plasma into an electric current. These devices are mounted in the sides of the plasma conduits to supply electrical power.
It is interesting to note that the Impulse engines are separate, and powered by their own Nuclear Fusion reactors. These reactors supply the impulse drive directly. As you know, the impulse engines are conventional magnetoplasmadynamic engines which provide thrust by using electromagnetic coils to emit bursts of accelerated matter. The impulse reactors can also supply enough power, via the EPS system and power transfer grid, to the rest of the ship, to maintain essential ships functions, life support, and some weapons capability. The impulse reactor systems also supply primary power to the inertial dampers that are necessary to counter the effects of time dilation caused by use of the impulse drive at higher, but sub warp, velocities. The inertial dampers on older vessels were powered from the primary EPS. This setup was changed after a notable incident with the Enterprise “B” model, where the inertial dampers failed at a critical trans-warp period. This situation nearly caused the loss of the entire ship and crew. The failure was later traced to inadequate output from the warp core.
Ship’s maneuvering Thrusters, on the other hand are high-efficiency reactant propellant types of thruster using on-board propellant created from some of the hydrogen that the Bussard collectors provide.
It should be noted that there are various other small fusion reactors throughout the ship. These reactors are of the Tokamak variety, and are essentially self-maintaining. Their primary purpose is to provide an uninterrupted flow of power to critical systems such as the EPS containment fields, and of course, the warp core. This entire system, the CIAS (Containment integrity assurance system) is completely self managing, and rarely mentioned in basic texts. It was instituted early in the starship program after the tragic loss of the USS Pernicious due to an EPS Conduit breach.
Before ending this discussion, it would be prudent to mention the ship’s computer systems. Although the interfaces to the computer core, as well as the core itself, are optical in nature, a large amount of energy is necessary to power this highly critical component. To that end, via the EPS, and a separate, redundant, DIPS (Data integrity power system), the ships computer core can draw on any number of power sources to maintain it’s functioning. This power flow is essentially uninterruptable, and completely automatic in function.