This concept, inertially confined fusion, is now 40 years old. It has taken that long to get the pulses powerful enough and narrow enough to have any chance of success. And the physics is still uncertain enough that their estimates of net energy gain range from 10 to 100. So I expect we’ll spend a decade or two developing and refining this process.
But we’re still a long, long ways from this to working fusion power. Here are just some of the problems we’ll need to solve before we can start building power plants:
1. How to make the process repeatable. Right now it’s one shot at a time; in order to build practical power plants, we need to be able to fire maybe 100 of these shots per second. That means that all the amplifiers must be recharged in 10 milliseconds. This raises extreme problems with power densities; this thing will need its own power plant just to start itself.
2. how to protect the equipment from the shock wave of the detonation. This thing will be like an internal combustion engine in the sense that it will go “bang, bang, bang” 100 times per second. Each of those bangs will be much, much bigger than the detonation we get inside a gasoline engine. All that shaking over years is going to create nasty stresses on the equipment, and if the equipment shifts position by tiny amounts, the reaction stops.
3. Neutron embrittlement. Fusion generates lots of neutrons. These radiate out and are absorbed by the surrounding materials. When a nucleus absorbs a neutron, it usually transmutes into another element. So if you’ve got a nice strong steel structure, after a while a lot of the iron atoms in the steel get converted into something else, and instead of solid steel you’ve got steel that’s full of contaminants. It loses strength and eventually falls apart. You’ve got to replace it before that happens.
4. Power capture. This thing has to get really, really hot. We need to carry away all that heat to make steam to drive turbines. So the entire assembly has to be bathed in water, and the water has to be moving through there at high speed. Now, water at temperatures of, say, 600ºF and at high pressures is a lot more corrosive than the water coming out of your tap. So you’re going to face serious corrosion problems for all those laser heads. Moreover, all that moving water must not be allowed to alter the positions of any of the laser heads.
Now, the general solution to all these problems is to use a double-shell system. The inner shell is a very strong evacuated sphere containing nothing at all; the fuel pellets drop down from above and the laser beams enter through long pipes. This shell gets very, very hot. The shell sits inside a much larger sphere through which water is being pumped at a high rate. All the laser heads, the pellet source, and the evacuating pumps are all outside the larger sphere, sending their stuff into the inner sphere through long (and very strong) pipes. This addresses a number of problems: the only things facing corrosion are simple pipes, easily replaced and strong enough to resist the force of the moving water. The water itself absorbs lots of neutrons, reducing the number that leak out to the outer equipment. And if you set the temperature and pressure of the water just right, you can have it right at the boiling point close to the inner shell, so that the shock waves compress the tiny bubbles of steam, which in turn acts like a shock absorber. Of course, if you get the temperature or pressure off by just a tiny amount, then you get trouble. And remember, the temperature varies all around the sphere. My guess is that they’ll need to develop a very complex swirling pattern for the water. And there’s still the problem of the temperature differential across the inner sphere skin. The inner surface of the sphere is going to be thousands of degrees hotter than the outer surface; that will cause it to expand much more than the outer surface, setting up gigantic stresses on it. My guess is that they’ll need to build a shell with wall structure that varies from inside to out—quite a piece of foundry work!
Overall conclusion: we are decades away from working fusion power. My guess is that we won’t see it before 2050.
