How close are we to having fusion reactors actually sending electric power to the grid? This is a huge and complicated question, and one with massive implications for our civilization. I think we are still at the point where we cannot count on fusion reactors coming online anytime soon, but progress has been steady and in some ways we are getting tatalizingly close.

One company, Commonwealth Fusion Systems, claims it will have completed a fusion reactor capable of producing net energy by “the early 2030’s”. A working grid-scale fusion reactor within 10 years seems really optimistic, but there are reasons not to dismiss this claim entirely out of hand. After doing a deep dive my take is that the 2040’s or even 2050’s is a safer bet, but this may be the fusion design that crosses the finish line.

Let’s first give the background and reasons for optimism. I have written about fusion many times over the years. The basic idea is to fuse lighter elements into heavier elements, which is what fuels stars, in order to release excess energy. This process releases a lot of energy, much more than fission or any chemical process. In terms of just the physics, the best elements to fuse are one deuterium atom to one tritium atom, but deuterium to deuterium is also feasible. Other fusion elements are simply way outside our technological capability and so are not reasonable candidates.

There are also many reactor designs. Basically you have to squeeze the elements close together at high temperature so as to have a sufficiently high probability of fusion. Stars use gravitational confinement to achieve this condition at their cores. We cannot do that on Earth, so we use one of two basic methods – inertial confinement and magnetic confinement. Inertial confinement includes a variety of methods that squeeze hydrogen atoms together using inertia, usually from implosions. These methods have achieved ignition (burning plasma) but are not really a sustainable method of producing energy. Using laser inertial confinement, for example, destroys the container in the process.

By far the best method, and the one favors by physics, is magnetic confinement. Here too there are many designs, but the one that is closest to the finish line (and the one used by CFS) is called a tokamak design. This is torus shaped in a specific way to control the flow of plasma just so to avoid any kind of turbulence that will prevent fusion.

In order to achieve the energies necessary to create sustained fusion you need really powerful magnetic fields, and the industry has essentially been building larger and larger tokamaks to achieve this. CFS has the advantage of being the first to design a reactor using the latest higher temperature superconductors (HTS), which really are a game changer for tokamaks. They allow for a smaller design with more powerful magnets using less energy. Without these HTS I don’t think there would even be a question of feasibility.

CFS is currently building a test facility called the SPARC reactor, which stands for the smallest possible ARC reactor, and ARC in turn stand for “affordable, robust, compact”. This is a test facility that will not be commercial. Meanwhile they are planning their first ARC reactor, which is grid commercial scale, in Virginia and which they claim will produce 400 Megawatts of power.

Reasons for optimism – the physics all seems to be good here. CFS was founded by engineers and scientists from MIT – essentially some of the best minds in fusion physics. They have mapped out the most viable path to commercial fusion, and the numbers all seem to add up.

Reasons for caution – they haven’t done it yet. This is not, at this point, so much a physics problem as an engineering problem. As they push to higher energies, and incorporate the mechanisms necessary to bleed off energy to heat water to run a turbine, they may run into problems they did not anticipate. They may hit a hurdle that will suddenly throw 10 or 20 years into the development process. Again, my take is that the 2035 timeline is if everything goes perfectly well. Any bumps in the road will keep adding years. This is a project at the very limits of our technology (as complex as going to the Moon), and delays are the rule, not the exception.

So – how close are they? The best so far is the JET tokamak reactor which produced 67% of net energy. That sounds close, but keep in mind, 100% is break even. Also – this is heat energy, not electricity. Modern fission reactors have about a 30% efficiency in converting heat to electricity, so that is a reasonable assumption. Also, this is fusion energy efficiency, not total energy. This is the energy that goes into the plasma, not the total energy to run the reactor.

The bottom line is that they probably need to increase their energy output by an order of magnitude or more in order to be commercially viable. Just producing a little bit of net energy is not enough. They need massive excess energy (meaning electricity) in order to justify the expense. So really we are no where near net total energy in any fusion design. CFS is hoping that their fancy new HTS magnets will get them there. They actually might – but until they do, it’s still just an informed hope.

I do hope that my pessimism, born of decades of overhyped premature tech promises, is overcalling it in this case. I hope these MIT plasma jocks can get it done, somewhere close to the promised timeline. The sooner the better, in terms of global warming. Let’s explore for a bit what this would mean.

Obviously the advantage of fusions reactors like the planned ARC design if it works is that it produces a lot of carbon-free energy. They can be plugged into existing connections to the grid, and produce stable predictable energy. They produce only low level nuclear waste. They also have a relatively small land footprint for energy produced. If the first ARC reactor works, we would need to build thousands around the world as fast as possible. If they are profitable, this will happen. But the industry can also be supported by targeted regulations. Such reactors could replace fossil fuel-based reactors, and then eventually fission reactors.

Once we develop viable fusion energy, it is very likely that this will become our primary energy source literally forever. At least for hundreds if not thousands or tens of thousands of years. It gets hard to predict technology that far out, but there are really no candidates for advanced energy sources that are better. Matter-antimatter theoretically could work, but why bother messing around with antimatter, which is hard to make and contain. The advantage is probably not enough to justify it. Other energy sources, like black holes, are theoretically and extremely exotic, perhaps something for millions of years advanced beyond where we are.

Even if some really advanced energy source becomes possible, fusion will likely remain in the sweet spot in terms of producing large amounts of energy cleanly and sustainable. Once we cross the line to being able to produce net total electricity with fusion, incremental advances in material science and the overall technology will just make fusion better. From that point forward all we really need to do is make fusion better. There will likely still be a role for distributed energy like solar, but fusion will replace all centralized large sources of power.