Fusion Future
What role will fusion energy play in the 21st century?
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We previously examined the merits of nuclear energy as a key part of a 21st-century energy mix, where I concluded that emerging Gen IV nuclear reactors promise to make energy cheaper, more abundant, and more environmentally benign. We focused our attention, however, on nuclear fission, where we split Uranium atoms to release their stored energy; we did not discuss the possibility of nuclear fusion. In a fusion reactor, instead of splitting atoms to unlock stored energy, we fuse them. Many consider fusion to be the “Holy Grail” of energy production, but like the Holy Grail, it remains elusive; a technology is always at least 20 years away. So what role, if any, could fusion energy play in the 21st century?
Understanding Nuclear Fusion
We might think of fusion as the “final boss” of energy production. Like fission, fusion can generate an incredible amount of energy with very tiny fuel inputs, but fusion can do it with no long-lasting radioactive waste. Fusion is also inherently safe; there is no possibility of a runaway reaction like there is with fission. Fusion is, after all, the energy of the stars; our Sun is just a giant fusion reactor, and most forms of energy here on Earth, whether it be coal, natural gas, or solar, are just an indirect form of fusion. Why then is it so difficult for humans to replicate what the Sun naturally does every day? Well, the Sun has an advantage. It produces fusion through its immense mass, enabled by its sheer size; its gravity compresses and heats Hydrogen atoms until they fuse into Helium.
Humans do not have the luxury of the vastness of space or gravity to do the work for us. Instead, we must recreate the conditions of the Sun in a confined location on Earth, and do so safely. For this reason, compared with fission, fusion has proven to be a much harder problem to solve. To maximize the probability that atoms fuse, we need to get atoms moving extremely fast. We do this by exciting them with incredible heat while confining them to a small area. The heat levels required are almost unimaginable; some 150 million degrees Celsius, which certainly will melt any containment vessel that we could conjure from Earthly materials. This problem is solvable, however, and there are two dominant approaches to this confinement problem: magnetic and inertial.
In an inertial confinement reactor, lasers are fired from multiple directions toward a single pellet of fuel. The aim is to heat the pellet so quickly that fusion occurs in its center before the atoms have time to wander off. This approach is proven to work and recently achieved net energy (more on this in a moment), but comes with a significant downside: the energy produced this way is discontinuous. It’s akin to heating a single pellet of coal in a coal-fired boiler, then needing to repeatedly swap in another and heat it again to release more stored energy. For this reason, magnetic confinement is the more popular approach for researchers aiming to produce a continuous energy stream. Magnetic confinement heats the fuel, usually contained inside a donut-shaped toroid, exciting the atoms such that the nuclei and electrons dissociate, creating a plasma, which can be contained using powerful magnets. As Incautious Optimism explains:
The plasma fuel in a fusion reactor isn’t just toasty warm, it’s also an electrical conductor. If you can induce an electrical current in the plasma loop, the interaction of that electrical current with the toroidal magnetic field will create a rotational transform, twisting the field into a helix. -And this helix will then cancel out the plasma drift and stabilize the magnetic trap, letting you hold onto your bottle of star stuff.
Magnetic confinement is an amazing juxtaposition, truly alien-level technology; immediately adjacent to the hottest man-made object, we must place some of the coldest superconducting magnets, powerful enough to contain the power of a star.
Fueling Fusion
Most fusion reactors envision using Deuterium and Tritium as their fuel. Deuterium and Tritium are hydrogen isotopes, the former with a single extra neutron and the latter with two extra neutrons. These elements are chosen because, compared with other theorized fuel types, D-T fuses at a lower temperature and releases more energy. A single gram of D-T, for instance, can produce the same amount of energy as found in 2,400 gallons of oil. As always, this comes with a trade-off: while Deuterium can be found in large quantities in Earth’s oceans, Tritium is extremely rare, radioactive, and has a 12-year half-life. The upshot is that we know how to produce more of it.
In what is perhaps the greatest international scientific endeavor of all time (aside from the International Space Station), countries around the world are working together to crack fusion through a project called the International Thermonuclear Experimental Reactor (ITER). Under construction in France, ITER will test our ability to produce this extremely scarce fuel using what is called a “breeding blanket.” Surrounding the reactor and made of Lithium-6, the blanket catches free neutrons from the reactor that are zooming off in all directions. The interaction of the Lithium-6 with the neutrons could create more Tritium than the plant consumes. Note that ITER will not have a full breeding blanket but aims to prove the basic concept for future reactors.
So, if we have solved the containment and fuel problem, why is fusion always relegated to being the “energy of the future?” The roadblock with fusion is not so much attaining it; it’s that it always requires more input energy than we can harvest in outputs. Even after some 60 years of research, our best magnetic confinement reactors have yet to achieve a q >1, that is, to produce net energy at the plasma level. But we’re very close. To be fair, inertial confinement has already reached q>1, but it’s unclear if pure inertial confinement will be scalable for commercial energy production. Even so, we are far from demonstrating that fusion can achieve net energy at the plant level, let alone one that can do so continuously, and be commercially competitive with other energy sources. We have come a long way, but we have a long way to go.
Furthermore, unlike solar and wind power, where we can mass-produce panels and leverage experience curve effects, most fusion reactor designs are large and will likely need to be custom-built on-site. This means that we can expect solar, wind, and possibly fission SMRs to advance much more rapidly than fusion in the coming decades. For these reasons, it seems unlikely that commercially viable fusion energy will arrive before 2050. Unless, that is, our approach to fusion, with our “either/or” choice between inertial/magnetic confinement, has needlessly pigeonholed ourselves into a technological dead end. Or, at the very least, thrown up technical roadblocks that are nearly impossible to overcome.
A Hybrid Approach
A secretive Washington-based company, called Helion Energy, is betting that’s the case. And while fusion startups are almost a dime a dozen, Helion has attracted some significant backing, including investments from OpenAI and Microsoft. They are developing a hybrid containment approach called magneto-inertial fusion (MIF), combining elements of both magnetic and inertial confinement. Their reactor isn’t a toroid; it’s linear, about the size and shape of a bus. Magnets at each end of the reactor form two separate toroidal plasmas consisting of ionized deuterium and helium-3 fuel, heated to millions of degrees. Magnetic fields then accelerate the two plasmoids toward each other at high speeds, causing them to collide in a central chamber. At that moment, additional magnetic coils, powered by supercapacitors, rapidly compress the merged plasma, raising its density and temperature to over 100 million °C, triggering a fusion reaction.
As with a pure inertial confinement design, Helion aims to harvest the energy created by these pulses, but they have an ace up their sleeve. Instead of harvesting the heat generated by the pulse to heat an intermediary, like water or helium, to drive a turbine and generator, Helion captures energy directly from the expanding plasma as it pushes against the surrounding magnetic field and uses it to recharge the system’s capacitors. They claim they can recapture over 95% of the energy expended triggering the pulse. This, they hope, will make it much easier to achieve net energy production at the planet level. Helion also diverges from the industry in fuel type, preferring to fuse deuterium with helium-3. This reaction is “aneutronic,” it produces mostly charged particles with minimal neutrons, reducing radiation and material damage, allowing the reactor to be smaller, cheaper, and require less shielding. In fact, they claim their design will produce significantly less radioactive waste than even a D-T reactor. Like D-T designs, their fuel cycle can breed more Helium-3, making energy production effectively limitless.
While I cannot speak for the physics or mathematics behind Helion’s reactor, the design is intriguing. It harkens back to the early 20th century “battle” between the steam and internal combustion engine (ICE), ultimately won by the ICE. Steam engines produced continuous power but required water as an intermediary; the fuel was burned to produce heat, which then boiled water into steam, driving a turbine and generator, etc, very much like traditional magnetic confinement fusion. Gasoline engines, on the other hand, combusted the fuel directly with tiny intermittent explosions, or pulses. Though initially more difficult to harness, ICEs proved to be lighter, more compact, and more efficient because the intermediary was not necessary. Compared to the ITER “steam engine,” Helion’s reactor is a piston engine; it does not need any turbines, water tanks, condensers, or any of their associated energy losses along the way. This also means that Helion’s reactor can be comparatively small and mass-produced in a factory. And that’s a big deal, for it will allow fusion energy to leverage experience curves alongside solar, wind, and fission SMRs.
Progress needs energy; it’s the fuel of our counterentropic endeavors. While efforts to improve energy efficiency, to make better use of existing production, are admirable, they will not take us very far in the 21st century, let alone the 22nd. The only path forward is to simultaneously raise our total energy capture as well. This is no trivial feat. Fossil fuels, the cornerstone of energy production since the Industrial Revolution, are ultimately a dead end. We won’t “run out,” so to speak, but declining energy returns on investment will make it such that growth will become difficult, if not impossible, in the coming decades. No, the future requires that we go directly to the source; either by harvesting sunlight as Mother Nature has learned to do, or by creating a Sun of our own.
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You and I agree that Nuclear is essential moving forward.
This piece really made me think about how your analogy of fusion being the 'Holy Grail' of energy production perfectly captures the persistent challenge and immense promise of this technology, which always seem just out of reach.