Question: At the moment nuclear fusion isn't very efficient due to the high temperatures it requires. Will we see the good effects of this sustainable energy source in our lifetimes, or does it still require a LOT of development before it can be widely used?

George Fulton answered on 5 Mar 2019:

Great question! It’s pretty widely agreed that the physics of nuclear fusion, the control of what we call the plasma (the soup of electrons and hydrogen), is well developed. The only nuclear fusion reactor using deuterium and tritium (two different forms of hydrogen) in the world, is in the UK. It’s called JET, but it was built before physicists knew how plasma behaved. It turns out that JET was simply too small to generate net energy. Here’s the analogy, if you were the fill a bucket full of hot water and a bath full of hot water, which cools down faster? The bucket right? JET is simply too small and it loses too much energy through radiative cooling. ITER on the other hand, is 8 times the volume of JET. It is a beast of a machine and so it won’t suffer from the same limitations! So from JET to ITER, there is not a whole lot of development that needs to be done, except logistically!

But size isn’t the most elegant solution. Nuclear reactors can be made more efficient by using more powerful plasma confining superconductors (magnets). This will allow much higher density of fuel and therefore increased chance of a fusion reaction. This requires significant development but has potential to be a big win in the fusion world. Large projects such as those at CERN, that use a similar technology mean that the development required might not be as bad as it might seem.

In short, I’m confident that nuclear fusion will be in the headlines in 25-40 years, so within our lifetime.