Feb 10 2022

JET Fusion Milestone

There is a lot of media buzz about the “fusion breakthrough” at the JET (Joint European Torus) experimental fusion reactor in Culham near Oxford, UK. Many people e-mailed me links to news reporting about it because they know I am a fusion enthusiast. But I am also a fusion realist. As I often have to point out, the current advance is nice but not really a breakthrough, and needs to be put into perspective. The risk is creating a premature sense in the public that the technology is imminent. Meanwhile I think we are likely still at  least a half-century away from having a working fusion reactor generating electricity for the grid.

Recent advances, however, cannot be denied. Fusion is a nuclear reaction that combines light weight elements into heavier elements, releasing massive excess energy. It is, as reporting almost always points out, the process that fuels the sun. Fusion, however, requires tremendous heat and pressure, and it is an incredible engineering challenge to generate those conditions on Earth. There are two basic approaches to doing this.

One method is inertial confinement, where lasers are used to heat a container causing that material to release massive energy causing inward pressure and heat (basically an inward explosion) that then causes the fusion. The National Ignition Facility (NIF) in the US is the primary experiment working on this approach. Just last month they announced that they achieved “burning plasma”. This also is a nice milestone, but needs to be put into perspective. Burning plasma refers to the state where most of the heat energy that is causing fusion comes from the fusion itself, rather than from an outside source. The next milestone is ignition, where the fusion generates more energy than the entire process consumes. Obviously we need to get there in order to have net energy we can siphon off to generate electricity, otherwise the whole project is just an interesting experiment. The climb from burning plasma to ignition, however, is steep.

The other approach is using magnetic confinement. The current cutting edge design that uses this approach is called a Tokamak, which is essentially a torus shape. The precise shape has been tweaked over the years, but essentially this uses powerful magnetic field to squeeze the plasma until it is hot and dense enough to fuse. This is the design of JET (hence the name). This approach is making progress, but is behind the NIF in terms of getting close to ignition.

JET is an experimental reactor, like all current reactors – not big enough to actually be a production fusion plant. Size does matter when it comes to fusion. In 1997 the JET facility broke the world record for the amount of energy produced by a fusion reaction, at just under 22 megajoules of total energy and 4.4 megawatts of power averaged over five seconds. That sounds impressive, but to be clear this is not net energy, this is the total energy produced by the fusion. It is still much less that the energy needed to get fusion to happen in the first place. Now, after improvements in the design, the JET facility broke their own record with a total of 59 megajoules of energy or  11 megawatts of power averaged over five seconds (still far short of ignition).

They did the experiment that produced this energy in order to better predict how the ITER will perform, and the experiment was considered to be under “ITER-like conditions”. ITER is a European project building the largest Tokamak fusion reactor to date, large enough (it is hoped) to achieve ignition and produce net energy. JET is being used to run experiments to test how ITER will perform, and that is what the most recent experiment was. For this experiment the JET facility updated their chamber with beryllium and tungsten, to better simulate the condition of ITER. These are both metals that have a very high melting point, which is needed to contain fusion.

Another aspect of the experiment was the fuel. Fusion reactors are designed to fuse hydrogen into helium, but there are different isotopes of hydrogen. Hydrogen-deuterium is the most commonly used, because these are both easily made on Earth in large quantities. However, hydrogen-tritium is a better fuel combination. The problem is that tritium is hard to make and is unstable, so doesn’t last for long. The current JET experiment that broke the record used hydrogen-tritium, again to better simulate ITER-like conditions. The reason it has been 25 years between records at JET is because of the unavailability of tritium.

If tritium is so rare, why is ITER planning on using it for fuel? Because they plan to use the fusion reaction itself to create more tritium fuel. The neutrons released by the fusion will interact with a blanket of lithium, and this process will generate tritium which can then be collected and fed back into the system as fuel.

Right now its a close race between Tokamak and inertial confinement in terms of which method will get over the finish line first, and likely will come down to NIF vs ITER. Perhaps neither of these facilities will achieve the final goal, and will just be one more stepping stone, serving as experiments that will help us design the facilities that will achieve ignition – sustained fusion generating excess energy.

Even if we do achieve ignition, however, there are still engineering challenges that need to be overcome. That 11 megawatts of power generated by JET was in the form of released neutrons. How do we turn those neutrons into electricity? The plan for ITER is to surround the fusion reactor with walls that will absorb those neutrons and heat up. Those heated walls will be cooled by water, which will turn into steam that will then run traditional turbines to generate electricity. Simple in theory, and will probably work out, but we need to do it.

I am a fusion realist, because I understand that developing practical fusion power is a massive engineering challenge and is taking longer than anyone thought 70 years ago when the fusion project began. It will likely take longer going forward than the most optimistic projections. But I am a fusion enthusiast because I do not see any reason why we will not eventually achieve fusion power. Once we do, it will be a game-changing technology. I think there will always be a role for solar power, because it can be small and distributed, and is getting cheaper and more efficient at a steady rate. But fusion has the potential to displace all other forms of energy.

Once we do achieve fusion it will likely be the primary source of power for human civilization indefinitely into the future, for thousands of years at least. It will fuel our ships, be absolutely critical for space stations and settlements, and create most of the energy we use. If it takes us even a couple of centuries of research and engineering to achieve that goal, it will have been worth the investment. We just need to have patience and realistic expectations.


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