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I've been busy looking into clean, sustainable energy solutions (for a project)

I ran into He-He fusion of the isotope He-3, and most of it looks more beneficial than the traditional D-T fusion due to its aneutronic reaction and more sustainable sources (apparently moon mining)

What stops us from putting the said fusion into practical use?

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    $\begingroup$ Well, the lack of mines on the moon kind of sticks out... $\endgroup$ – Jon Custer Dec 1 '19 at 22:24
  • $\begingroup$ There's some useful info at this related question: physics.stackexchange.com/q/326077/123208 He-3 fusion reactions require a much higher temperature, and are thus harder to initiate and harder to control. $\endgroup$ – PM 2Ring Dec 2 '19 at 1:30
  • $\begingroup$ Helium 3 is just really expensive and is mostly gathered from the products of nuclear reactors (the other kind), so it being less radioactive in fusion reactors is perhaps a moot point. $\endgroup$ – aquirdturtle Dec 2 '19 at 4:50
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    $\begingroup$ I believe it is a great idea to use helium 3 as a fuel. using helium-3 could therefore provide a highly efficient form of nuclear power with virtually no waste and no radiation $\endgroup$ – Jack Rod Dec 2 '19 at 7:33
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What is the largest obstacle in practical helium-3 fusion?

I just found this now, sorry for the tardy reply.

Very simply, He-3 requires much higher temperatures to occur, occurs less often than D-T even at those temperatures, and produces less energy when they do occur.

Since a working reactor should produce more energy than it consumes, the fusion reactions have to be plentiful enough to produce more energy than is being naturally lost to the surroundings through convection and radiation - the same as any hot object. When the self-heating from the fusion events provides enough energy to keep the fuel hot on its own, we call it "ignition" or a "burning plasma".

The rate of losses goes up with temperature, so He-3's higher operational temperature means higher losses. Combine that with lower rates of production and lower output from those events, and you have an extremely difficult problem. In overall terms, D-He-3 fusion is perhaps 1000 times more difficult than D-T.

We've been working on D-T for many decades now and we're still about another decade away from that hitting ignition. So He-3... well, that's just not going to happen.

Now you will easily find any number of people claiming they have some sort of shortcut to He-3 fusion. You can discount any such claim.

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I hope this article help which I got from the mentioned website.

https://www.explainingthefuture.com/helium3.html

Helium-3 is produced as a by-product of the maintenance of nuclear weapons, which could net a supply of around 15Kg a year. Helium-3 is, however, emitted by the Sun within its solar winds. Our atmosphere prevents any of this helium-3 arriving on the Earth. However, as it does not have an atmosphere, there is nothing to stop helium-3 arriving on the surface of the Moon and being absorbed by the lunar soil. As a result, it has been estimated that there are around 1,100,000 metric tonnes of helium-3 on the surface of the Moon down to a depth of a few metres. This helium-3 could potentially be extracted by heating the lunar dust to around 600 degrees C, before bringing it back to the Earth to fuel a new generation of nuclear fusion power plants.

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