It’s 2020. Let’s Talk About Fusion.
Nuclear Fusion Part 1
The world is a strange place these days. Let’s spend a moment thinking about strange and new things in an entirely different area: future energy technologies.
- Fusion can supply unlimited, reliable and clean energy.
- The physics of ignition (net energy gain) and the business case must still be proven.
- Advances in key technologies, computational power and simulation tools, available research facilities, and the increased presence of business-minded entities have made inertial confinement fusion (ICF) approaches less crazy, and maybe even feasible.
- As the late Carl Sagan said, we are all made of stars.
In this series we are exploring fusion because it can massively alter the energy landscape of the future. Fusion is incredibly attractive as an energy source because:
- It can be built anywhere in the world (no pipelines, wind, or sunshine needed).
- Fusion can support an almost infinite increase in energy demand because the fuel is essentially unlimited. This includes increasingly dense population centers.
- The supply chain can be entirely located within a country for energy independence and reduced price volatility.
- Fusion provides baseload power, complementing intermittent energy sources like wind and solar.
- Fusion power is clean — no waste or pollution is produced.
While nuclear fission (what we refer to as nuclear power today) is a carbon-free source of baseload power that is well established, there are several reasons that fusion would be even better. The fuel used by nuclear fission plants, Uranium-235, can be enriched to make bombs, leading to nuclear weapons proliferation concerns. Nuclear plants also generate some radioactive waste , and there is the low probability of an accident leading to release. (Although as someone who has worked in nuclear power plants, I would happily live next to one.) Currently, the most significant barrier to building new conventional nuclear (fission) plants in the US is economic — the cost per kW of new capacity added simply isn’t competitive with other forms of energy generation. 
Nuclear fusion is essentially the opposite of nuclear fission, which powers nuclear plants today. In nuclear fission, a single large atom, usually Uranium-235, breaks into two smaller atoms and releases energy. In nuclear fusion, energy is produced when two atoms are smashed together to become one larger atom. This process is what powers the sun, and has produced all the heavier elements in the universe.  On earth, the atoms used for fusion are usually isotopes of hydrogen, the lightest element on the periodic table. 
The question isn’t “is fusion possible”. The hydrogen bombs that were tested in the 1950s (now in the arsenal of most of the world’s nuclear powers) are called hydrogen bombs because most of their energy comes from the fusion of hydrogen isotopes. Their precursor, the atomic bomb deployed by the US in WWII, instead produces energy from nuclear fission of enriched uranium or plutonium. In a hydrogen bomb, fusion is triggered by a mini-atomic bomb (fission of uranium or plutonium), releasing incredible amounts of energy. While the hydrogen bomb program demonstrated that fusion can occur with sufficient energy input, it’s worth noting that it relies on enriched uranium or plutonium to work — fusion alone has not been weaponized.
Since then, we have found ways to achieve fusion other than by detonating atomic bombs. The challenge is providing enough energy to overcome the repulsive forces between atoms. Once this energy barrier is exceeded, the two atoms fuse together- the new atom weighs a tiny bit less, and that extra mass is converted into lots of energy. This is an example of Einstein’s famous equation, E (energy) = m (mass) x c (speed of light)². Unfortunately the repulsive forces between atoms are so strong that the fuel (e.g. hydrogen) must be brought to millions of degrees C without melting the container or letting it cool off.
One strategy is to use powerful magnets. At these temperatures, gases become plasmas, which conduct electricity. Because of how magnetic fields and electric fields interact, magnets can be used to keep the high temperature plasma away from the walls while the fusion reaction takes place. This approach is called magnetic confinement fusion (MCF), and the machine that results looks like a giant robot donut.
The second major non-bomb strategy uses lasers and is called inertial confinement fusion (ICF). A small amount of fuel is released into a chamber and then zapped with powerful lasers that quickly heat and compress the fuel before it can fly apart. We will talk more about inertial confinement fusion technology in the next post, but for now remember that there are two main routes to fusion power: magnets and lasers.
Instances of fusion of light atoms have been observed in research facilities all around the world. However, it has always required more energy to make the fusion happen than is released when the atoms come together.
For fusion power to go from dream to reality, two things must happen. First, ignition, or net energy gain, must be achieved — this is the holy grail of all fusion programs. However, to really change the world, fusion companies must also show a credible path to power plants that are not only safe and reliable, but also make economic sense. More on both topics to come in this series.
Looking back at past promises and news articles, it is easy to understand the joke — “fusion is always 20 years away”. The process of getting two atoms close enough together to fuse is incredibly complex and difficult to model. Then it takes a ton of energy and complex equipment to test if the model is right. For many years, the money required (and in some cases weapons implications) meant that research fusion was run by government research efforts and was often classified.
Fusion research was slowly declassified and merged with civilian and academic plasma physics research, but fusion projects were still by necessity “Big Science”. The mainstream coverage of fusion that most of us remember (circa 2000s) involves ITER, an enormous international MCF (magnet fusion) project under construction in France that began back in 2007 and recently reached the half-way mark in construction. Much will and has been learned from ITER about materials, design, diagnostics, and plasma physics (not the least training thousands of scientists and technical tradespeople), but it is envisioned and structured as a research project, not a business.
In the past ten years, several companies have been created to commercialize new fusion concepts and the advances made in research. Startups such as Commonwealth Fusion are demonstrating that magnetic confinement fusion might be possible on a smaller scale and development timeframe than ITER. Importantly, they are leveraging development of superconducting magnet technology (which has applications beyond fusion) to make a business case.
Inertial confinement fusion (lasers) has seen the most exciting changes in the last decade. Advances in key technologies — lasers and optics, materials, and sensors (often driven by non-fusion applications) have reduced potential costs and enabled new approaches to achieving ignition. The impact of increased speed and power of computation also cannot be understated. Without good simulations and knowledge of the underlying physics, designing a fusion experiment (let alone a power plant) is an expensive trial and error process. The ability to include more physics and materials properties in simulations has enabled better experiment and equipment designs with fewer false starts and failures.
Without good simulations and knowledge of the underlying physics, designing a fusion experiment (let alone a power plant) is an expensive trial and error process.
Complementing the great strides in simulation capabilities, several state-of-the-art facilities for laser-based plasma physics research have come online in the last 10 years, enabling more laser experiments with higher power and more precision than was ever possible. The increase in both computation and laser capabilities has vastly increased the knowledge base and confidence of the fusion community. This also means that there is now an expanded network of user facilities that early-stage fusion companies can use to prove out their technology, rather than having to spend tens if not hundreds of millions to build these facilities right out of the gate.
This combination of factors — advances in key technologies, the speed and power of computation, available research facilities, and increased presence of business-minded entities — brings inertial fusion energy into the realm of possibility. This will be an interesting space to watch.
Fire the lasers! In the next post, we’ll dive into inertial confinement fusion (ICF) technology. This will help inform discussions of how fusion might compete on a cost basis, and what’s in store later in this series.
- The amount of waste generated from nuclear power plants is surprisingly small. All of the high-level radioactive waste ever produced by the world’s nuclear power plants would fit in a building 10 ft high and covering an area the size of a soccer field (Source: 2018 IAEA report, pg 39).
- There are many reasons for this, but insurance and regulatory costs play a significant role. More than 50 nuclear (fission) power plants are under construction in other countries, mainly China.
- The energy our sun produces comes from the fusion of hydrogen atoms to form helium (the second element in the periodic table). This happens in the sun’s core, a dense ball of plasma (the state of matter that is hotter and denser than a gas!) that is at a temperature of millions of degrees C.
Convincing helium and larger atoms to fuse together takes EVEN MORE energy than fusing hydrogen. Scientists believe that carbon, oxygen, iron, and all the other heavier atoms were formed in the massive energy release accompanying a Supernova, or the death of a star. The building blocks for everything in our bodies was likely born in a star halfway across the universe. (I just think this is beautiful.)
- An isotope is an atom with more neutrons than usual. Hydrogen (1H) has only one proton and a molecular weight of 1. Deuterium (2H), has one proton and one neutron. Tritium (3H) has one proton and two neutrons.
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