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!!
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.