What is Fusion?

Example 33.17 (D–T, weighed)

Before: $2.01355 + 3.01550 = 5.029\,05\,\mathrm{u}$; after: $4.00151 + 1.00866 = 5.010\,17\,\mathrm{u}$; so $\Delta m = 0.018\,88\,\mathrm{u}$ and $E \approx 17.6\,\mathrm{MeV}$, four fifths of it on the neutron — less than a fission, but from five nucleons instead of $236$: about $3.4 \times 10^{14}\,\mathrm{J}$ per kilogram of fuel, four times fission. Helium-4 (Example 33.6) is once again the ash.

Example 33.21 (The energy ladder, per kilogram)

Energy per kilogram of fuel: coal, $3.0 \times 10^{7}\,\mathrm{J}$; uranium-235 by fission, $8.2 \times 10^{13}\,\mathrm{J}$; deuterium–tritium by fusion, $3.4 \times 10^{14}\,\mathrm{J}$; total conversion ($E = mc^2$), $9.0 \times 10^{16}\,\mathrm{J}$. Six orders of magnitude separate chemistry from the nucleus — the reason a reactor is refuelled by the truck and a coal plant by the trainload.