How close are we to nuclear fusion?

In recent days, there have been interesting developments in the field of nuclear fusion. American researchers claim they have successfully conducted experiments that could make the process easier. Meanwhile, British scientists have unveiled a special type of reactor - which they say offers new ways of controlling the white hot plasmas generated by nuclear fusion. But are we really any closer to solving one of science’s greatest mysteries? Here’s fusion physicist Brian Appelbe, from Imperial College London…

Brian - Fusion is essentially just a way of making nuclear energy, but it's not like the normal nuclear energy we get from power plants which is fission energy which is based on splitting the heavy atom. Instead, nuclear fusion is when we join light atoms together to release energy. It is very attractive because it essentially gives us much more energy per unit mass than we can get from fission or all other energy resources, and it is also a much cleaner form of nuclear energy than fission. However, it is tremendously difficult to do because in order to make fusion energy, we essentially have to make something that is as hot as the centre of the sun in order to induce the nuclear reactions within it.

Chris - Indeed, because of course we know fusion works, we just look up in the sky to see it at work, it's bathing us in glorious sunlight and warmth. But the sun has the advantage that it's about a million times bigger than the earth and millions of degrees in the middle, isn't it? It has some of the problems solved. How are scientists trying to surmount the fact that we don't have a sun to hand?

Brian - Exactly correct. It's really a question of containment or confinement. So with the sun, we make it very, very hot. When you make something very hot, it wants to explode, it's got a lot of energy, it's under high pressure, it will attempt to explode. The sun stays contained because it is so massive there's a huge gravitational force that keeps it confined whereas, on earth, when we want to generate nuclear fusion energy, we must find alternative manmade ways of confining this very hot material in which the nuclear reactions are happening. Scientists have looked at various ways of trying to confine this very hot (what we refer to as) plasma. When we make the nuclear fuel very hot, it becomes a plasma and scientists have found various ways of confining or containing these hot plasmas, for example, as has been in the news recently, using a magnetic field.

Chris - There's an announcement this week about a wonky or twisted donut. They're dubbing it the 'stellarator.' This is the company or the group Type One Energy. They're enthusiastic about this. Why do they think this will be the game changer or a contributor to becoming a game changer?

Brian - There are many reasons for the excitement, some of which are based on science, more of which are based on economics and money. In particular, the accelerator is a design in which you essentially twist the magnetic field lines to make them into a closed configuration in a manner that very effectively contains this hot plasma. The announcement is Type One Energy, this private fusion company, have got a particular design which they think, on paper, should be able to give them a net energy gain, i.e. get more energy out of the system than you're putting into heat and confine the plasma in the first instance. But much of the excitement about this is because of technological developments that we've had over the last few years. The basic accelerator design itself dates back to I think the 1970s, but what's advanced a lot in the intervening years is technologies like superconducting magnets that actually make it efficient to generate these magnetic field configurations.

Chris - They're saying they want to have a plant to test this active in Tennessee by 2025. That's literally next year.

Brian - Which is very ambitious. You know, I guess it is nice to see such ambition. I've been working in this field for over 10 years and in the last maybe five years there's been a lot of excitement, partly because there's lots of money being invested in the field, there's lots of startup companies that are pursuing different designs, planning to do lots of exciting things, and I think it's very difficult to evaluate all of these in isolation. What we look at is the fact that across the whole field we're seeing a lot of advances both on the scientific and on the economic side of things. It's following a pattern where we've got a lot of companies and laboratories who are making a lot of rapid progress.

Chris - And you talk about the advancements in the science right on cue because there is a paper in the journal 'Nature' this week looking at this. What are they doing and saying?

Brian - This is quite interesting because this is very much a scientific development in fusion. This is a different form of twisty magnetic fields. This is the tokamak, which is essentially a donut shape of magnetic field lines. And there is the DIII-D tokamak in San Diego run by General Atomics, that's a well established device that they've been doing experiments on for a very long time. But they've made a breakthrough in which they've found a way that they can actually keep their hot plasma contained using the magnetic fields, but they've increased the density of the plasma which they're containing quite significantly. That's very exciting because essentially the denser the plasma that we're confining, the more nuclear reactions can happen and the more efficient the whole process can be. So by making lots of the subtle changes to their system at DIII-D, they've been able to increase the density above what was previously thought to be the upper limit on densities that could be contained. From a scientific point of view, this is a very exciting development for tokamaks. The big question with this is how it scales up to larger tokamak devices because the DIII-D device is actually very small by the standards of tokamaks. It's only, I think, of order about two metres in diameter whereas the biggest tokamaks that are currently being planned and built are tens of metres in size; an order of magnitude bigger. What's not clear yet is how the results from DIII-D could actually scale to these larger machines.