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A simple Google search reveals dozens of articles about the clean fusion energy that can be obtained from Helium-3. As Helium-3 is highly scarce on Earth, there are many spectacular schemes for obtaining Helium-3 from extraterrestrial sources such as the soil of our Moon or the gas of Jupiter. It seems the advantage of Helium-3 over Deuterium is that it's aneutronic and therefore much cleaner without the harmful fast neutrinos of a classic fusion reaction. But there are many other sources of clean, aneutronic fusion that can be obtained from less scarce sources. For example, the p-Boron aneutronic fusion reaction. With Boron being so readily available, why is so much imaginative energy spent on future schemes of obtaining Helium-3? What am I missing? Thanks!!

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  • $\begingroup$ Wikipedia says that the fusion reactions from He-3 create much more energy than those from B $\endgroup$ – Jim Mar 20 '15 at 16:21
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The main problem with boron (relative to 3He) is that the atomic number is high. This means that the plasma must run at a considerably higher temperature, about a factor of 10, in order to overcome the Coulomb barrier. Higher temperature means faster electrons in the plasma. Faster electrons means more radiation when the electrons "hit" the walls. This radiation, Bremsstrahlung, is X-radiation. The energy lost to Bremsstrahlung is about 1.5 the energy gained by fusion.

Also, the reaction cross section, at best, is five times lower for boron fusion.

Not to mention the engineering difficulties in dealing with the X-rays.

So choose your poison: the difficulties of boron or the scarcity of 3He.

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  • $\begingroup$ I would bet that boron fusion reactors will be working long before NASA gets to the moon again $\endgroup$ – user56903 Mar 20 '15 at 17:41
  • $\begingroup$ Could be, but there is reportedly enough 3He available on earth for small applications: nuclear submarines, rocket engines, etc. $\endgroup$ – garyp Mar 20 '15 at 17:56
  • $\begingroup$ @garyp I'd be interested (seriously, no sarcasm here) to see that report about $^3He$. I can't find a reaction that will produce it artificially. The magazine Physics Today has several news articles in the past 2 years about how helium is going to be a regulated quantity, especially $^3He$. It's used in super-cooling dilution refrigerators at national labs. $\endgroup$ – Bill N Mar 20 '15 at 21:41
  • $\begingroup$ the natural decay of Tritium produces <sup>3</sup>He $\endgroup$ – lurscher Mar 20 '15 at 23:12
  • $\begingroup$ ${}^3$He is generated during the maintenance of the US nuclear weapons arsenal, but I don't know the details of how. Published estimates place the size of the US stockpile at 30 kg, but I've heard someone in the fusion business express skepticism; the true size is classified, and certainly larger, in his opinion. But he doesn't really know. $\endgroup$ – garyp Mar 21 '15 at 1:53

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