Record-Breaking Spherical Tokamak Promises A Fusion Revolution
The tokamak strikes back.
A recent study found that the ST40, a spherical tokamak fusion reactor, reached the astronomical temperatures of 100 million degrees Kelvin. That is 6.7 times hotter than the core of the Sun! This insane temperature is enough to create fusion ignition, which can potentially create commercially viable fusion power! But what the hell is ignition, or a spherical fusion reactor for that matter? And does this mean we are on the cusp of unlocking this utopian energy source?
Let’s start at the beginning. What is fusion? And why is it the ultimate clean energy source?
Nuclear fusion is the process that powers the Sun. The Sun is mostly made of hydrogen, and in its core, the temperature and pressure are so high that collisions between hydrogen atoms have enough kinetic energy to overcome the forces that keep atoms apart. These collisions cause the two hydrogen atoms to fuse together into a single, bigger helium atom, but a helium atom is lighter than two hydrogen atoms because it needs fewer gluons (fundamental particles that keep an atom’s nucleus together). The famous E=MC2 equation by Einstein states that a tiny amount of mass is equal to a huge amount of energy. This means that a single fusion reaction releases an enormous amount of power via radiation and heat.
If you fuse 17 tonnes of hydrogen, the energy released would be enough to power the entire US for a year. That equates to only 0.05 grams of hydrogen per US citizen! Furthermore, helium is the only gas released throughout this process. With its amazing fuel efficiency and zero carbon emissions, fusion power is one of the most eco-friendly energy sources on Earth.
Our fusion reactors try to recreate the conditions in the Sun’s core to utilise this process to make energy. The only problem is that it currently takes more energy to recreate these conditions than the energy we can extract. This is because the pressure at the centre of the Sun is so massive that consistent burning fusion happens at only 15 million degrees Kelvin. Meanwhile, in our far less pressurised reactors, we need to reach temperatures far, far higher. These massive temperatures, combined with losses in the reactor, meaning that energy demands to run these machines are insanely high! As such, viable fusion power remains a sci-fi pipe dream.
However, there have been recent breakthroughs here. Last year, the National Ignition Facility (NIF) was able to create a net-gain in energy from a single reaction. Their reactor is an inertial confinement design. This design uses high-powered lasers that fire at a hydrogen-containing pellet, and the explosion this creates is hot enough and dense enough to trigger fusion. Back in December 2022, one of NIF’s reactions reached temperatures over 100 million degrees Kelvin, which created ignition.
Ignition is when energy from fusion reactions heats up the plasma further, triggering more fusion reactions. You can think of this as a self-sustaining burn or as a fusion chain reaction. At colder temperatures, the majority of the particle collisions in the plasma have way too little energy for fusion. But at temperatures over 100 million degrees kelvin, the particle collisions that don’t have enough kinetic energy to fuse are only marginally off. This means that the extra heat from nearby fusion reactions creates more fusion, and the chain-reaction is kicked off.
During ignition, less energy input is needed for energy output, as fusion happens without needing more energy. This is how NIF was able to create a net-gain in energy from a reaction.
But a new study found that an entirely different reactor, UK-based Tokamak Energy’s ST40 spherical tokamak, has also reached temperatures of over 100 million degrees Kelvin! This is a record-breaking temperature for a tokamak reactor, and Tokamak Energy has even said this is the temperature needed to unlock viable commercial fusion.
In fact, this is, arguably, a more significant advancement for fusion power than NIF’s net-gain in energy. Why? Well, it’s all to do with the advantages of tokamaks. Let me explain.
Tokamaks are a type of magnetic confinement fusion reactor. You see, at these insane temperatures’ hydrogen isn’t a gas but rather a plasma, and plasmas interact with magnetic forces. A tokamak uses ultra-powerful electromagnets to squeeze and heat a hydrogen plasma within a doughnut-shaped reactor to create fusion.
While tokamaks were some of the earliest forms of fusion reactors, they have long been plagued with low efficiencies and unstable plasmas, which both led to decreased temperatures and massive net losses in energy. As such, over the past few years, they have lagged behind their inertial confinement counterparts.
But, ST40 is a spherical tokamak. This means its reactor is taller and skinnier than a traditional tokamak, so that rather than resembling a doughnut, it resembles a cored apple. This is a relatively new design, and it greatly aids plasma stability, which can increase pressure and temperature within the hydrogen dramatically. This is why the ST40 was able to reach record-setting temperatures of over 100 million degrees, despite being far more compact and less powerful than many other tokamaks.
So, why is this important?
You might think, “So what? NIF is already there.” Well, actually, no. The amount of energy released by NIF’s milestone reaction was tiny, and it takes days to refuel the machine, which severely caps the overall energy output of this type of reactor. This is further compounded by the fact that their laser can only fire at full power a few times a year; otherwise, it risks breaking. As such, NIF simply can’t build a usable fusion power plant.
But tokamaks are different. They can operate for much longer periods of time, and can reload and go again far, far quicker. As such, if Tokamak Energy can use their ST40 to recreate the ignition seen at NIF, they have a far more promising pathway to creating a viable commercial fusion power plant.
Now, there are still plenty of hurdles for Tokamak Energy to overcome. For one, they need to translate this high energy into sustained ignition. But they also need to make the tokamak itself and the energy capture systems efficient enough as not to cancel out the potential energy gain from the fusion (i.e. losses in the machine are still greater than the potential gain in energy from the reaction). Neither of these milestones has yet been hit, and fusion will continue to elude us until they are met. However, through Tokamak Energy and their remarkable ST40, we now have another pathway to crossing these bridges and unlocking the most planet-friendly energy source possible.
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