To the outside observer, the fusion core is the most spectacular feature of the Jupiter 2, with its ring of brilliant flashing lights beneath, and the last feature visible as the craft ascends into the night sky. As it turns out, the flashes of light are typically understated in fictional representations, and are even more spectacular than more people believe who have only seen popularizations and not the actual phenomenon. We'll get into that in greater detail below.
The fusion core is probably the single most critical piece of equipment aboard the Jupiter 2, providing power not only for the engines and subwarp ring, but for all other systems aboard the craft as well. Failure of virtually any other single unit can be compensated for in some way or another, but failure of the fusion core would leave the ship stranded and the crew probably dead. Fortunately, it is a robust if moderately complex device with quite a bit of built-in redundancy.
Deutronium and the Beryllium Cycle
Deutronium is the fuel that powers the fusion core, and indirectly the entire spacecraft. At first glance, even the scientifically educated wonder exactly what deutronium is. It sounds like a metal, but there is nothing with that name on the periodic table, all the way up to element 124. The term deutronium was coined by Wilma Karacin, one of the researchers in the early days of quantum coupling fusion research for one of the experimental fuels: beryllium deuteride. This is, of course, chemically identical to beryllium hydride, except that the hydrogen is replaced with deuterium, giving the molecules an additional two neutrons each. These two are essential for completion of the beryllium cycle which makes possible quantum coupling fusion at low temperatures and with a recyclable component. Other effective fuel mixtures were discovered, but "deutronium" remains the most efficient and practical.
The reaction proceeds in two steps. First, a molecule of deutronium is fused into an atom of heavy boron:
This isotope is inherently unstable, but a second quantum coupling stage helps it along:
Energetic helium is, of course, the desired reaction product, and the beryllium is recycled to make it feasible to manufacture fresh deutronium in the field.
The fusion core consists of 36 individual channels. We'll take a look at how one of those is put together.
The first stage of the reaction consumes energy, and this is made available in the form of kinetic energy. In addition to this energy requirement, rapid movement of the reaction components — and at the exact velocity demanded by mathematics — is required for the quantum coupler to work correctly.
The fusion core accomplishes this with some relatively simple and well-established technology: an ion source and a travelling wave tube. The ion source, much the same as used in particle accelerators since the hour of their invention, uses a high potential electric field to strip electrons from a deutronium molecule. The deutronium is ionized in short pulses of about 100 microseconds. The resulting positively charged particle can then be accelerated by electromagnetic means.
The exact means chosen is a travelling wave tube. These were once used in communications as amplifiers by accelerating electrons. Here, they accelerate pulses of charged deutronium. The system consists of an array of synchronized microwave oscillators arranged to create an oscillating electromagnetic field that travels lengthwise down the tube, hence its name. The wavefronts of energy accelerate the pulse of deutronium by "pushing" it along. The kinetic energy of the deutronium is dependent on the speed of the wavefront, which is determined by the frequency of the microwave oscillators. Since it is routine to control frequency to better than one part in a billion, the speed of the deutronium pulses is controlled with similar accuracy, well within the required tolerance of the quantum coupler.
The Quantum Coupler
The quantum coupler (or perhaps couplers, since there are actually two active units) is the heart of the fusion core, and along with the subwarp ring likely represents the highest level of technology aboard the Jupiter 2. Both also remain classified, so we are unable to present details. However, the basic principles are known, so we shall proceed with those.
A quantum coupler window consists of alternating layers of atoms of carefully chosen elements. It is the exact choice and arrangement of elements, along with the fabrication process, which remains classified, but that doesn't stop speculations. Many authorities in solid state physics believe that the first window (the one mediating the deutronium-to-boron reaction) consists of layers of silicon, lithium, and copper. There is quite a bit of controversy and no clear consensus on the composition of the second, although rumors persist that germanium is in the mix.
Regardless of the exact elements, what is important is that this repetitive arrangement of atomic nuclei at precisely calculated intervals yields a periodic potential field of precise wavelength. Think of it as a quantum wave frozen in space. Likewise, the precisely controlled pulse of deutronium has a quantum wave of its own. The interesting stuff happens when the two meet.
Because of the peculiar interaction of these two waves, the deutronium pulse doesn't see the window as matter at all in the ordinary sense, and tunnels right through it. There is no collision, which prevents the window from being eroded away. But more importantly, the spatial quantum wave presented by the window mediates the nuclear reaction by coupling the deutronium quantum wave to the boron quantum wave, in the case of the first window. Furthermore, and critically, it does this in such a way that the boron atom has a lower net energy even though its actual rest energy is greater. This forces the reaction forward with nearly 100% efficiency.
The second window is even more interesting. Of course, it mediates the fission of boron-12 into beryllium and helium, but there is more to it than that. This reaction liberates a tremendous amount of energy, and if it came out as heat as did early fusion experiments, the window and perhaps the entire fusion core would vaporize instantly. That would be catastrophic.
Instead, the static wave of the second window is tuned so that nearly the entire kinetic energy portion of the reaction product is directed along the original path. It is this factor of the second window that introduces so much controversy among experts: no one outside the government laboratories really understands how it works. At any rate, the result of all this is a pulse of completely ionized beryllium and hydrogen nuclei travelling at nearly the speed of light toward the end of the fusion core channel. The electrons have been left in the dust, so to speak.
Even though the reactions in the quantum coupler windows is very nearly 100% efficient, the amount of total energy that passes through is so vast that even a small inefficiency results in dissipation of fairly large amounts of heat. About 90% of this is in the first window. In fact, the net dissipation is sufficiently large that it is impossible to operate a single fusion core continuously. The quantum coupler windows are mounted in a copper block cooled by liquid nitrogen, but even so the device must be operated in pulsed mode.
This accounts for the various segments that compose the fusion core. The channels fire in rapid succession in a round-robin fashion, giving each one time to cool before it fires again. Typically, in what is called binary mode, two opposing channels fire simultaneously. This provides enough power to supply both the inertial drives and subwarp ring, as well as other onboard systems. At rest, such as on planet when it is necessary to recharge onboard systems, the fusion core can be operated in "lean" or unary mode where only one channel fires at a time. Conversely, during periods of extremely high power demand — such as emergency acceleration using the inertial drives — it is possible to operate the fusion core in ternary mode, firing three at a time. Extended use of ternary mode is dangerous and can lead to the overheating of the fusion core.
At this point, we are left with a tiny cloud of essentially 100% ionized helium and beryllium travelling at roughly 99.997% the speed of light. This represents quite enough energy to blast right out the bottom of the spacecraft, and enough of a magnetic field to pull a nail right through your hand should you be foolish enough to be holding one nearby. It is the job of the extractor to get this energy under control before it destroys the craft.
It accomplishes this by treating the high-energy pulse as the primary "winding" of a transformer. The extractor consists of 120 layers of hypermagnetic core sandwiched between layers of quartz. For those not in the know, hypermagnetic core is sort of the magnetic analog of a superconductor: it supports astronomically high levels of magnetic flux in a small cross-section.
As the pulse passes each magnetic core element, it induces a magnetic field. A staggered array of secondary superconductor windings translates this to usable electrical energy, to the tune of a few hundred volts and several hundred amperes per secondary, on average. An array of solid state rectifiers converts this electrical energy from alternating to direct current. It is still pulsed, but this form of power just as good as pure direct current for charging the main accumulator, from which all ship's systems derive their power.
This extraction of energy of course slows the pulse as it travels the length of the extractor, so each successive stage is somewhat less efficient than the one before it. Also, remember that the pulse is nearly completely ionized, so it consists of a tremendous net positive charge that is trying to push it apart. At high velocities, its own magnetic field tends to keep it focused, but as it slows, it does manage to expand. Therefore, the latter of the magnetic core rings has an ever enlarging opening for the beam, giving an overall cross-section rather like a trumpet. This also contributes to the lower efficiency of the latter stages.
And here comes the spectacular part and the more information about that factor that we promised above. As physicists know, the acceleration (or deceleration, which is the same thing) of an electrical charge radiates electromagnetic energy. Here, we have the tremendous deceleration of a tremendous charge. The resulting flash of light has a smooth emission spectrum actually hotter (more energy in shorter wavelengths) than the sun, more after the order of an electronic strobe. Rather than try to absorb this radiated energy and deal with it, the designers decided to just let it out. This accounts for the choice of quartz as the separating material between the magnetic elements; it is transparent to the considerable ultraviolet component of the flash, which is also nearly as bright as the sun. It also accounts for the famous flashing lights of the fusion core. Many popular representations show the sequential flashes more like a string of Christmas lights, but imagine if you will a series of ultra-powerful strobes going off in rapid succession, bright enough to light the nighttime countryside for miles. It is truly a spectacle to behold.
After everything else is said and done, we are left with a cloud of nearly motionless but heavily charged helium and beryllium, neither of which can be left in the channel because they would interfere with subsequent operation of the fusion core. Since the cloud is positively charged, an electric field diverts it into a circular trough toward the center of the craft. Here it is neutralized and the gaseous helium continually removed with a diffusion pump. The beryllium collects on the negatively charged collection plates as a fine dust. During maintenance cycles this chamber is flushed with pure water to collect it for recycling. Human contact with the beryllium is avoided at all stages because it is quite toxic.