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The Future Of Fusion? Meet The Stellarator

Written by TKS Boston Student, Amelia Settembre (email: amesett@gmail.com)

Power and energy are essential parts of our everyday life. Every time you turn on a light, you’re using power. If you’re reading this online, you’re using energy. If you’re watching a video — you guessed it — you need energy. So that means that with so many people needing power and energy, we’re brought into a world that’s demanding more and more power. What’s more, getting this power is the hard part.

So humans came up with this idea of using one of the processes most commonly seen in the stars: nuclear fusion. Stars typically do this to gain their fuel, and the process is pretty simple and quick (at least, for a big gaseous body like a star). Here’s a quick rundown on how power transfer works when concerning nuclear fusion.

  1. Two elements have their respective makeup fused together, and reform. In a deuterium and tritium fusion, the two elements reforms into a helium atom and a neutron.
  2. The “extra” mass left over is reconverted into the kinetic energy of the neutron. This is what you get from Einstein’s famous equation, E=mc². Here, the energy equals the mass times the speed of light squared.

Deuterium is found pretty commonly, about on part per every 6,500 of seawater. Tritium is less common, but is still available. Because these two elements are the most easily accessible, they’re what we use most commonly on Earth when performing nuclear fusion.

Nuclear fusion also needs relatively hot temperatures in order to occur, usually happening at around 100 million kelvin. This, of course, is a relatively difficult temperature to achieve, especially when looking at finding it anywhere near Earth. The element which we consider to typically be this hot is plasma, which is also relatively difficult to make.

Plasma In Nuclear Fusion — The First Try Tokamak

At some point in recognizing the importance of plasma in fusion, scientists asked themselves if they could apply plasma to a machine so that fusion could occur within. This first device was called a tokamak. Tokamaks are doughnut shaped machines which cage plasma in ionized magnetic fields as they heat them to insane temperatures.

In an explanation completed with a more complicated diagram, this is the inside of a ITER Tokamak. It is able to hold the plasma secured in one place while utilizing the inside of the reactor to generate energy from the fusion.

The Tokamak worked something like this: in order to continue fusion, it was necessary to maintain certain particles in the plasma close to the center of the machine. This was done by using magnetic force to take advantage of the Lorentz force which was already experienced by the particles. This just meant that the magnetic and electric influences on the particles helped to keep them in helical paths along field lines.

In addition to this, it was found that Tokamaks would also benefit greatly from having a spiral loop around the center which would help the particles flow more easily — as compared to a simple circle. This adjustment was found in the later Stellarator.

Over all, Tokamaks are relatively simply design-wise, and also a convenient source of power. They were invented in 1960s Russia in order to generate power via fusion efficiently, and have been successful. However, as stated before, the Tokamaks weren’t perfect and still needed some adjustment before they could be more successful and widely used. One of these early changes was known as the Stellarator.

Tokamak 2.0 — The Stellarator

More recently, in a lab in the corner of Germany, scientists have been hard at work looking at a possibility for an improved version of the tokamak. Now the largest existing stellarator, meet the Wendelstein X-7.

The stellarator is similar conceptually to the tokamak — it’s able to contain plasma and generate energy, which is ultimately the goal. However, tokamaks are better more generally at keeping the heat inside the device, which is needed to maintain the plasma and thus the reaction. Stellarators also tend to veer on the more-difficult-to-make side, and are almost impossible to set up fully functionally.

On the other hand, stellarators are much better at keeping the process going, and aren’t typically prone to having magnetic disruptions which bend the metal around tokamaks and can ruin the entire process. Not only that, but they also are much more likely to work better when put into the scheme of being part of a functional fusion power plant.

Right now, the build of one has a series of materials, which make it difficult both to have conceptually and physically, although the WX-7 has demonstrated that it is, indeed, possible to make.

  • Vacuum-shaped container. This allows the magnets, which are at -270 C to be as close as possible to the 100,000,000 C temperature of the plasma without destroying either the magnets or the plasma.
  • Twenty flat, superconducting magnets help to make careful adjustments to the magnetic field. This keeps the plasma able to flow, and grants the ability to make the small adjustments as necessary.
  • The plasma is contained in a twisting shape, caged in by the superconducting magnets to stay consistent in form. It also keeps all particles within the machine.


Tokamak on the left, stellarator on right. This is a comparison of the two images, and both are pretty different (although similar).

The doughnut shape does cause some problems, though. These problems consist of having a magnetic field that’s stronger near the inside and weaker near the outside. Because of this, particles are more likely to stray from the inside and bounce out of line. To avoid this, the twist is put into the stellarator, so that the regions with more strength and those with less are offset, and they cancel each other out.

What This All Comes Down To

  • Energy is super important in our everyday lives, and one of the good ways about going and getting it is fusion. This is used typically by stars to generate heat and light.
  • On Earth, fusion involves plasma in order to have a hot enough temperature to keep the reaction going consistantly. This is difficult to achieve, unless you have the right means.
  • The tokamak was one of the early designs featuring a way to maintain plasma. It was first implemented in Soviet Russia, and was not unsuccessful although it did have problems (such as metal-bending fluctuations in the magnetic field).
  • Later still came the stellarator, which is similar to the tokamak in principle but features adaptations (like having a winding path for the plasma to travel, which makes it less susceptible to fluctuations).

Ultimately, stellarators still have a long way to come before they can be used perfectly in generating energy, but as science has shown us, we’re not too far behind.