Three Fusion Reactor Variations

Synopsis:
A number of different methods have been suggested and tried, with respect to the goal of achieving controlled nuclear fusion for power production. It seems to me that some of those techniques are "complementary", such that if combined in an overall system, the whole would be a more effective means of reaching the goal. The particular techniques under consideration here include high-pressure hydrogen gas, laser ionization, solid-hydrogen pellet acceleration/collision, and theta pinches.

The Details Begin:
NOTE: I shall be using the word "hydrogen" herein a great deal, while the particular varieties involved are probably going to be deuterium, or a deuterium/tritium mixture, or even a deuterium/helium-3 mixture. But "hydrogen" is encompassing enough, and simpler to write. Anyway, the quest for controlled nuclear fusion has been taking too long, partly because the task is not simple, but also partly because resouces devoted to the goal have been divided into umpteen different schemes, all of which are somewhat promising, but few of which seem able to be sufficiently workable in the final scaled-up form of a power reactor. I am bothered by the fact that people know full well that many inventions come about from different things being combined together, yet as far as nuclear fusion research is concerned, the researchers are largely divided into camps, each of which thinks its own approach is the One True Way. There are the magnetic confinement people, the electrostatic confinement people, the inertial confinement laser-blast people, the inertial confinement electron-blast people, the inertial confinement sonic-blast people, and so on, and so on, and so on. Bah!

Some History:
It was known back in the 1950s that the temperatures needed for nuclear fusion were extreme. There was an obvious problem in trying to "hold onto" multimillion-degree matter, while trying to force atoms to merge together. Still, it was known that at high temperatures atoms shed electrons and matter becomes a mixture of bouncing ions -- all of which are electrically charged and can be manipulated by magnetic fields. More, a plasma can also conduct electricity, and that electric current also generates a magnetic field. This magnetic field can squeeze or "pinch" the plasma, making it more dense and making fusion more likely. Unfortunately, the "pinch effect" tended to pinch the plasma unevenly, causing, for example, a pinch of the plasma into two separated blobs -- which breaks the flow of electric current and terminates the magnetic field that does the pinching!

Well, an alternative to the simple pinch was to generate the squeezing magnetic fields using ordinary external wiring. This quickly evolved into a huge curved conductive piece of metal (a "single-turn coil"), into which an enormous amount of current was dumped from a giant bank of capacitors. The volume of plasma within that "coil" became brutally squished to very near the fusion point; some of the first recorded controlled fusions, in fact, came from this "theta pinch" device. But it had its own flaw, in that to operate most efficiently, it needed to START with a DENSE volumous plasma -- something which still cannot be contained today with external magnetic fields.

Next, the inertial-confinement people deal with extremely dense plasmas, which they make on-the-fly from small amounts of solid or liquid hydrogen-containing substances. The blast of energy that that small volume of material receives is sufficient to cause compression and heating, ionization, and also some fusions. These researchers mostly have the problem of trying to apply that energy to all sides at once, perfectly evenly, of the small volume of material, lest it be kicked sideways (out of the center of the reaction chamber) and impact/damage their equipment. And, of course, small volumes of material lead to small amounts of fusion, so far insufficient to pay for the energy-blasts.

Perhaps you can now see the gist of what I am about to suggest here: The inertial confinement approach should be used to generate a decent volume of dense plasma, and the theta-pinch approach should then squeeze that dense plasma to the fusion point. Some of the details that I am going to present, however, you may find a bit surprising, especially if you are already familiar with the many existing approaches to controlled nuclear fusion power, so please bear with me. :)

Start With A Cylinder...
In essence, a single-turn theta-pinch coil is the body of a simple cylinder, with a single slice down its length. Electricity is fed into the cylinder all along one side of that slice, and after it flows around the body of the cylinder, the current flows away from it all along the other side of that slice. The Greek letter Omega (capitalized) looks something like a cross-section of a theta-pinch cylinder, including attached electric feeds. Note that the overall orientation of this cylinder -- horizontal or vertical -- will depend on choices made as this description continues.

The fact that this cylinder has a slice down its length means that if we want to use it to hold a vacuum (the typical environment for controlled-fusion plasmas), then we have to seal it (and, of course the ends of the cylinder) with some sort of nonconducting material. Glass, ceramic, or some other stone-like substance will probably do fine (have to watch those thermal expansion coefficients of differing materials, but they do that already, in such mundane realms as light-bulb manufacturing).

Add Some Hydrogen-Rich Material...
This could be as simple a thing as injecting a frozen-solid-hydrogen pellet (vertical cylinder). Then we blast it with a laser from each end of the cylinder, which plasma-izes the pellet, after which we SQUISH it with the main theta-pinch pulse.

Or we could take fresh liquid hydrogen and use magnetism to separate the naturally magnetic "ortho-hydrogen" form from the naturally non-magnetic "para-hydrogen" form. (Background Info: Ortho- and Para-hydrogen molecules are distinguished from each other by the way the two electrons are mutually oriented with respect to a property called "spin". Each electron-spin is associated with some magnetism; if the two electrons spin oppositely, the magnetism cancels and the result is para-hydrogen. If they spin the same way, the result is the slightly more energetic ortho-hydrogen molecule. At room temperature, there is enough ordinary thermal energy so that a significant percentage of hydrogen is ortho, but that percentage gradually diminishes at liquid-hydrogen temperatures, as ortho changes to the para form.) With our fresh liquid ortho-hydrogen, we now freeze it into pellets, and immediately use these pellets two at a time. We put them into coil guns! We magnetically accelerate them to perhaps a hundred kilometers per SECOND, and shoot them into our cylinder (horizontal orientation), directly at each other. They collide (and cancel their overall motion) most spectacularly, almost instantly converting into a single dense plasma blob-- every molecule is moving at plasma-temperature-speed, see! -- which we immediately SQUISH with the main theta-pinch pulse. The reason for this variation is that magnetic acceleration is much more energy-efficient than the process of creating a laser pulse, and ALSO more efficient than the process that converts laser energy into hydrogen plasma.

Or we could fill our cylinder with pressurized hydrogen at ordinary temperature. If we wanted to be extreme, we could pressurize it until it becomes liquid, but I doubt that this will actually be necessary. Now we shine an ultraviolet laser beam down the middle of the cylinder. This not-very-powerful beam has to be UV light of a particular frequency (the primary "Lyman" spectral line). When a UV photon of this frequency is absorbed by a hydrogen atom (and this particular frequency is easily absorbed), the hydrogen instantly ionizes. The net effect of shining this UV laser beam down the axis of the cylinder is that we create an ionized pathway, which is able to conduct electricity. Now we discharge a small bank of capacitors, creating a minor artificial lightning bolt through the hydrogen in the cylinder, which of course follows that ionized pathway. Since lightning is always accompanied by thunder, and since we are involving highly pressurized hydrogen here, the "boom" is going to be quite notice-able. This "boom" will ECHO off the walls of the cylinder!!! -- and form a sonic compression wave that will naturally squeeze the hydrogen at the central axis of the cylinder. We can add another UV pulse and another capacitor discharge -- none individually need to be very powerful, but the resonant accumulative effect is going to cause a significant volume of very hot dense plasma -- which of course we SQUISH with the theta-pinch pulse. (For anyone who thinks that this whole reactor might explode like a bomb, well, I suppose it will depend on just how compressed the hydrogen is, in the cylinder, before lighting the laser. Fusion reactions ARE damped quite easily, due to ordinary matter being extremely cold, relative to the temperature required for nuclear fusion. Still, if it DID explode, you couldn't say that this technique didn't pass break-even, could you? :)

Extract The Energy:
The first two notions will require that cylinder be lined with heat-absorbing fluid, which in turn flows to a heat-exchanger to generate steam for turbines. They also have a comparative weakness with regard to neutron-absorption; they will become radioactive more quickly than the compressed-hydrogen cylinder (hydrogen is a GOOD neutron blocker!) Also, the third proposal offers a one-step way to extract energy, because instead of using an intermediary heat-transfer fluid, that tank of compressed hydrogen merely needs to have some plumbing leading to a heat-exchanger, which makes steam for turbines. Also, of course, we will want to filter out waste helium-4, before returning the fuel to the reactor cylinder.