Well, one gets only so much energy out of every reaction. But this is such an absurd amount of energy that it's hardly the technological bottleneck. The nuclear

Well, one gets only so much energy out of every reaction. But this is such an absurd amount of energy that it's hardly the technological bottleneck. The nuclear physics of fusion is the easy part. To get a burning fusion reaction, you need to satisfy the Lawson criteria [1], which can be seen as a constraint on the "confinement time", into which goes all the plasma physics. Empirically and theoretically, the most important factor in maximizing the confinement time is the strength of the magnetic field. We can just about able to create magnets that are strong enough, but they aren't strong enough structurally: the force they exert on the plasma is enough to break the magnets themselves. From what I've seen and heard, the two most important bottlenecks are structural strength of strong (superconducting) magnets, and the robustness of blanket material to neutron bombardment. [1] https://en.wikipedia.org/wiki/Lawson_criterion https://en.wikipedia.org/wiki/Lawson_criterion