There's no such thing as a single "breakthrough" in fusion, and it bugs me whenever news outlets claim it's "just around the corner" or "it just requires a geni

There's no such thing as a single "breakthrough" in fusion, and it bugs me whenever news outlets claim it's "just around the corner" or "it just requires a genius to figure it out". Fusion is achieved by many incremental improvements on the design of the facility, the macroscopic structure of the fuel, and its material makeup. There are two ways humans can have self-sustaining fusion. See my crappy log-log plot: http://i.imgur.com/ZfCueCe.png http://i.imgur.com/ZfCueCe.png Inertial confinement fusion starts at the red point and goes straight up without heating up the plasma much. After it stagnates for ~2-5ns, the high-pressure plasma equilibrates so its temperature rises, putting it in the fusion range. The higher the pressure, the higher the final temperature, and ideally you want to get as deep into the fusion range as possible to more efficiently burn the fuel. The state of art neutron energy yield per laser capacitor yield is around 100%, but we need at least 5000% to make up the inefficiency of charging capacitors, amplifying lasers, converting neutron kinetic energy into steam, generating electricity via turbines, and still have some left over to supply a power grid. Magnetic confinement fusion starts at the red point and goes to the right over a few milliseconds. The pressure is always about 1 atmosphere, so you have to get really hot. Tokamaks can hold this position for a few seconds, which is needed for efficient fusion to account for the slow burning because of low pressures. I'm not sure exactly what the engineering challenges of magnetic confinement are, but I can say that storing anything that hot for a while is very damaging to the tokamak, while at the same time you must have strong and precise magnets placed around it. There's really no other way of getting into that "fusion" area of the plot. If you try to draw a diagonal line, you wouldn't be able to keep pressurizing because high temperature makes plasma difficult to compress. You have to choose one of the above two general methods, and the design space is pretty well explored, so there's not going to be a large breakthrough that researchers have completely missed at this point. Fusion will be achieved by a sequence of 1% improvements month by month, so law makers and tax payers must understand this when they allocate X dollars and are disappointed that their grant only gave a 10% improvement on previous methods.