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In this universe contained self sustaining fusion has been achieved. As we know the fuel for fusion is most commonly isotopes of hydrogen, and helium is produced as a byproduct of that.

Helium is, as far as im aware a worse fusion fuel. So my idea is that only rich can afford hydrogen for the best burning fuel. They then sell the waste helium. So poorer people have to use lower concentrations of hydrogen, and more helium

The problem is that I’m not sure if this would make sense, as hydrogen is very common, why couldn’t poor people just get it anyways and not have to use a waste product. Basically I’m not sure how to fix these holes with my idea.

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This isn't quite what you described, but may be usable for your purposes.

Hydrogen comes in three different isotopes -- H1 (protium), H2 (deuterium, also D), and H3 (tritium, also T). H1 and D are both stable; D is very roughly one part in a hundred thousand of naturally occurring hydrogen. Both H1 and D are trivially separable from seawater or other water, and it is relatively trivial to separate D from H1. T, on the other hand, is unstable, hard to concentrate, and hard to store.

H1 fusion is not really viable as an industrial process, although at scale (think: stars) it's a great approach.

This gives us two main paths to fusion power: D+D and D+T.

For your world, D+D is "high class" fusion power. The fuel for it is so cheap as to be free; but the capital expense of building a D+D fusion plant is prohibitive. Deuterium fuses with deuterium at temperatures above 400 million degrees, and this isn't easy to reach! But in exchange for building such a high-tech power plant, D+D fusion is relatively clean; one of the few waste products is Tritium, which is stable enough (in the scheme of things) to not damage the plant itself much.

D+T is, in comparison, poor man's fusion. It can run at much lower temperatures -- 45 million degrees or so -- which makes it much easier to get a plant up and running. But you have to source the darn tritium from somewhere. And while there's various ways to get tritium, probably the easiest is to pay the D+D fusion folk (and be beholden to them) to get their waste products. D+T is also a much dirtier fusion -- it produces a higher flux of neutrons which will activate (make radioactive) the fusion plant itself, limiting its life time and making the plant's eventual disposal and rebuilding a future problem.

This (very simplified) description gives you two levels of fusion technology, one that favors capital availability with both a better product and a recurring input stream; the other of which allows a bit of "mortgaging the future" to at least get large amounts of power off the ground. A bit of Vimes' theory of nuclear boots, as it were.

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  • $\begingroup$ D+D does produce neutrons and produces only a third of the energy of D+T. Tritium could be bread either from Lithium or Helium3 in any reactor with high neutron flux (for example a D+D reactor). However, it is only worthwhile due to its low ignition point. D +He3 is where it is at for the high quality fusion plants. Or better yet the CNO-cycle, assuming you got the technology. $\endgroup$ May 3 at 18:01
  • $\begingroup$ D-D fusion is not cleaner than D-T. D-He3 fusion is cleaner. $\endgroup$
    – Avun Jahei
    May 3 at 18:52
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I could write a long answer. But I could also point you to Atomic Rockets article on choosing your fusion fuel. Scroll down a bit and you will see a nice table explaining most common fusion reaction. Below there are details about their applications.

The gist is that neither what we usually call hydrogen nor what we usually call helium is great as fusion fuel outside of stars. Apart form the CNO cycle that the biggest stars use, where you get fun returns like 350% more energy for every 10% increase in temperature. Getting that to work is rather challenging though. Read Clarke-Tech, which is indistinguishable from magic.

The interesting stuff are isotopes of hydrogen and helium. Specifically:

  • Deuterium: hydrogen with an extra neutron; get it from water or out of a gas giants atmosphere
  • Tritium: hydrogen with two extra neutrons; radioactive and rare in nature, you manufacture it by bombarding either lithium or helium3 with neutrons on the proper energy level
  • Helium3: helium with one instead of two netrons in addition to the two protons; rare on Earth, mine it from the atmospheres of gas giants (or the Moon/Mercury if you are a masochist)

The fusion reactions and their applications, thus inplied (social) status are:

  • He3-De: very few neutrons (De-De side reactions), highest energy output, moderately hard to ignite, common ressources if space can be accessed, used in most reactors
  • De-Tr: lots of neutrons (not nessessarily bad as they can be used to breed more Tritium, though you won't break even), slightly less energetic than He3-De, easiest fusion reaction to ignite, De is common but Tr needs to be produced, only used if ease of ignition is a factor as it would be in weapons and propulsion systems
  • De-De: lots of neutrons, significantly less energetic than the alternatives, hardest reaction to ignite of the three, De is very common in water and on gas giants, used as a poor man fuel in the Oort-Cloud and on embargoed worlds as well es in beeder reactors in the atmospheres of gas giants to transmute Helium3 into Tritium

In summary, your social status idea makes little sense. There is no perfect fuel, there is only the fuel that fits your circumstances best. I could imagine that De-De fuel could develop a bad reputation, as, as it is used in industrial facilities and by fringe groups, reactor savety standarts might be sub-par and the applications aren't prestigious. This is the closest your are likely to get to the system you want.

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    $\begingroup$ 1. "De-Tr: lots of neutrons (not nessessarily bad as they can be used to breed more Tritium, though you won't break even)" - Breakeven is possible if lithium-7 is used as target material. It produces tritium WITHOUT consuming the neutron. $\endgroup$
    – Avun Jahei
    May 3 at 18:55
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    $\begingroup$ 2. "De-De: lots of neutrons, significantly less energetic than the alternatives" If all side reactions are included neutron production and energy production are quite similar to D-T fusion, but yes, much harder to achieve. $\endgroup$
    – Avun Jahei
    May 3 at 18:57
  • $\begingroup$ @AvunJahei Thanks for the pointing out my mistakes. I'm still not certain on how the economics of using lithium for breeding works out relative to the usage of helium3 as the fertile feedstock. He3 is still four orders of magnitude more common than lithium. So I'm not sure that the poor neutron economy is that relevant to a space-fareing civilization. $\endgroup$ May 4 at 5:07
  • $\begingroup$ @AvunJahei De-De's side reactions are the results of the Tritium and Helium3 being produced during the reactions? $\endgroup$ May 4 at 5:08
  • $\begingroup$ @DyingOfLight I am not sure why you say that " He3 is still four orders of magnitude more common than lithium." Lithium has an abundance of 17ppm on Earth and 2ppm in meteorites. Helium3 is almost non-existent on Earth and should have an abundance of less than 10ppm in the atmosphere of gas giants. $\endgroup$
    – Avun Jahei
    May 4 at 12:29
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Neither normal helium nor normal hydrogen can be used as fusion fuel, so the whole plot is impossible.

Fusion fuels are deuterium, tritium and helium-3 (ignoring proton-boron fusion).

enter image description here

Deuterium is easy to get by isotope separation from any natural occurring hydrogen source (water for example).

Tritium must be produced, either from lithium or from helium-3 (3He + n -> T + p!). Both methods use reaction with neutrons, tritium supply therefore depends on neutron supply. Tritium is also a by-product of deuterium-deuterium (D-D) fusion.

Helium-3 is difficult to get on Earth, but can be mined in the atmosphere of the gas giants (or on the Moon, but reserves are much more limited). Tritium decays into helium-3 with a half-life of 12 years. Like tritium helium-3 is a by-product of D-D fusion.

Note: you can produce both tritium from helium-3 and helium-3 from tritium, and both can be produced from deuterium if you have a D-D reactor.

Using pure helium-3 as fusion fuel (number 4 in the picture) is the cleanest option, because it does not produce neutrons, but it is also the one hardest to achieve. That would be the "rich man's fuel".

The reaction D-He3 is a bit easier to achieve and more energetic than pure He-3 fusion. But it is not as clean, because neutrons are produced by D-D side reactions.

The reaction D-T is the easiest to achieve, almost as energetic as D-He3 but also the dirtiest option, because it produces the most neutrons, so it would be the "poor man's option"

D-D is a special case. It is more difficult than D-T fusion and provides only a forth of the energy. However, it produces useful products: tritium and helium-3. Also, in a real life reactor, those products would react with the deuterium and also with each other (unless you separate them) resulting in energy output similar to D-T fusion.

In your plot the "poor man's fuel" is a waste product of the "rich man's fuel". That is not really the case and I can't see a reasonable way to save that part of the plot.

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Healthy part is the energy rationing. If something is abundant, it does not mean it has to be available to anyone on equal basis. Energy in this case is a product of product of product of product of technological product of a society or humanity in general, a result of collective work. It needs to make all those fusion reactors, maintain them, improve, make all kinds of science and technologies and researches.

So in this setting availability of energy based on merrits - it can be a fair enough system. And if no matter which specifics are of that merrit system it possible to have poorer and richer people, so as super rich and poor.

In a sense you do not have to invent anything in this setting, if you wish so and story/history of this setting is in this way - it all busness as usual, and fusion by itself does not bring the change. Same way as presence of solar panels and sun light does it not, or wind or hydro or nuclear power, or whatever.

Another few major resources people do not have equal access to, even if they are abundant - is land, fresh water, oxygen(I had to mention it - one eats less he uses less oxygen), sun light.

What you do with fusion can be a way out for different inequalities, if you do it, but not the fusion itself. I mean fusion offers opportunities, but are those opportunities persued is a different a story based question.

As a note, helium is not only a worser fusion fuel, but if compared to D+T it like burning rocks instead of coal (which also not that easy to ignite and burn) - I mean it totally a different beast. Here is a list of valid options https://en.m.wikipedia.org/wiki/Fusion_power#Fuels

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Often easy to get/cheap resources will not be available to the poor, as laws will be put in place to protect their status. A good example of this is silk in ancient times, which became more available to the places around china as china manufactured and traded more of it. Many of the rulers in those places made it illegal for the less wealthy(although not poor, more middle class/merchants) to wear silk.

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I'm not sure what you're trying to accomplish with this story idea.

If you just want to have a society where the rich have abundant energy and the poor don't, you don't need to get into this "levels of fuel" business. Hydrogen as an element is abundant, but it's not like you can just go in your backyard and pick up a bucket full of hydrogen.

And in any case, while hydrogen is plentiful, fusion reactors are not necessarily cheap to build and operate. If and when fusion becomes a viable source of consumer energy, it's not at all clear from present technology and engineering how much it will cost. Who knows what technologies will be invented in the future? But if present trends continue, fusion plants will be huge, very expensive operations. A poor person will not be buying his own personal fusion plant to run in his basement.

So just like today, the rich can afford all the energy they might reasonably want to run a home, while the poor struggle to pay the electric bill and have to scrimp and save.

Is there some reason why your story needs different fuels, as opposed to people plugging in to an electrical network like today? If so, I'd think a more plausible angle would be different purities of the fuel. Hydrogen comes in several isotopes. You need deuterium or tritium to run a sustained fusion reaction. Deuterium and tritium occur naturally in any mass of hydrogen but in very small quantities, so the hydrogen must be run through a centrifuge or some other process to increase the concentration of deuterium. I think it more likely that if there were different "grades" of fusion fuel in a society, that it would be hydrogen with different concentrations of deuterium.

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    $\begingroup$ “it's not like you can just go in your backyard and pick up a bucket full of hydrogen.” You kinda can though. You know. Water. $\endgroup$
    – Topcode
    May 3 at 22:35
  • $\begingroup$ @Topcode What I was trying to say was, you can't just pick up a bucket of hydrogen that you could then use for nuclear fuel. Yes, water contains hydrogen, and you can extract the hydrogen by electrolysis. Then you have to centrifuge it to get the Deuterium concentration up to usable levels. That's not a free and easy process. (Maybe other ways to accomplish the goal, I don't know off the top of my head. But I'm sure any alternatives also require serious effort.) $\endgroup$
    – Jay
    May 4 at 17:12
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Probably the other way around

As a rule, the proton-proton chain is more readily accessible in a star, versus the triple-alpha process that needs a hotter environment to get past an unstable intermediate.

The "poor" would be those who can only mimic reactions in the core of the Sun that would take billions of years under those conditions, while the "rich" can take their helium waste product and fuse it.

Now, there's an odd caveat to this - despite all the fancy tech needed to fuse the helium, the power output is not better, but worse. The rich don't care, of course; they can have more reactors. The real point is, the rich people's reactors can generate lithium and beryllium by triple alpha, and can easily move on to CNO cycle reactions. With advanced technology, they can generate a huge array of isotopes - light ones, at least - and have the power to make things. That's not really a good enough plot explanation (asteroids are cheap), but perhaps they can also make exotic matter we haven't yet discovered. Elongated nuclei with super-fast spins that fuse together into neutronium-like cables or something. I don't know, this is a few thousand years past my tech grade. But there's more variety in those cycles than in just fusing some protons.

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