There’s a joke in physics that asserts that the time until commercial fusion power generation becomes viable is 15 years - and has been since 1940. Maybe that 15 years is a constant of nature, and like a jogger on a treadmill there’s no forward progress despite all the effort in the world.
Maybe, but there’s reason for optimism. Unlike the treadmill, there is forward progress being made. But let’s step back and ask why we should care. The answer is pretty simple: the world needs more and more power because technological devices need electricity. And especially as China and India develop at great speed, the total number of people using lots of electricity increases dramatically. Right now we get most electricity from fossil fuels. These generate enormous amounts of pollution, and add to the level of CO2 in the air. Renewable power is nice and getting better, but they tend to be rather poor at providing base-load power. Wind and solar farms take up valuable space and fill the local environment. Startup costs are very large.
Nuclear power is very promising, but the public tends to be wary of it. Chernobyl is impossible in a modern design and radioactive waste is fairly easily and safely stored, but the stigma is prohibitive. Further, fuel is not incredibly cheap and they require lots of valuable water for cooling. I think nuclear fission is still the best of the currently viable alternatives to fossil fuel, but it’s far from perfect.
That’s where nuclear fusion comes in. Like the sun, it fuses light atoms (hydrogen isotopes, generally) into heavier ones (helium, generally). Radioactivity is produced, but in vastly smaller and easier-to-handle amounts than in nuclear fission plants. But to get fusion to work, the power plant has to produce conditions of extreme heat and adequate pressure to get the hydrogen to fuse in the first place. On one hand this is a perfect safety feature. If a breakdown ever occurred, damage to the reactor instantly destroys the conditions necessary for continued nuclear reactions. And since only a very small amount of fuel is reacting in a given time, a problem instantly and automatically prevents the reactor from causing
melting down. It’s a physical impossibility.
Unfortunately, those extreme conditions of temperature and pressure are very difficult to achieve. Thus far, it takes much more energy to generate those conditions than it the reactor produces. In the early years of nuclear fusion the reactions required millions of times more energy than they produced. Now it’s much less of a hurdle - depending on how optimistic various theoretical considerations are assumed, we might even be within a factor of 2 of true breakeven. Once we reach the level of breakeven, it’s possible we will have found a low-cost, safe, and powerful source of abundant energy fueled by the hydrogen found in all water.
ITER is the next step in this process. It is expected to operate at several times higher than breakeven, but it’s not possible for this design to actually generate electricity. It’s just a proof-of concept. Here’s hoping it works spectacularly well!