It's the theoretical breakeven event (Q=1) when you use high power lasers rather than the magnetic confinement of a tokamak. The NIF is doing research on this i

It's the theoretical breakeven event (Q=1) when you use high power lasers rather than the magnetic confinement of a tokamak. The NIF is doing research on this inertial confinement fusion, where they shoot a lot of power with lasers on a tiny pellet with hydrogen. So you get extreme densities and temperatures, but not a lot of confinement time, i.e. the ions cool down _really_ fast. That shifts the curve a little bit. In my opinion, it is a bit misleading to add this to the plot, because for this laser-based fusion, the theoretical breakeven lies really far from the practical, commercial breakeven. But as shown there on the gif, the NIF did manage to cross the Q=1 for inertial confinement fusion last year!