How fusion power works

The sun is a gigantic fusion reactor that creates nearly all of the energy making life on earth possible. Sunlight provides the warmth that keeps water from freezing, and sunlight lets plants create the food that animals need.

What if we could take the fusion principles seen in the sun and bring them down to earth in a miniaturized form? If we could do that, it would be possible to generate all of the electricity that humanity uses. We would not need to release any more of the carbon and pollutants generated by coal-fired power plants. We could also do away with the most of the high-level nuclear waste produced by traditional nuclear power plants.

Scientists and engineers have been working on fusion power for decades.

Why are there no fusion power plants? Because it is very difficult to create a mini-sun. The temperatures involved are mind boggling. Let’s look at the basic idea behind fusion to understand where the temperatures come from.

Hydrogen atoms are very common on earth. Each water molecule, for example, contains two of them. The goal of a fusion reaction is to press two hydrogen atoms together so tightly that their atomic nuclei fuse with each other to create a single helium atom. The nucleus of any hydrogen atom has one proton. The nucleus of any helium atom has two protons. In the fusion process, two hydrogen atoms become one helium atom. As the helium atom is produced, fusion releases a huge amount of energy.

The problem is that protons have no desire to get together. Because they have the same charge, they repel each other in a way that is similar to magnetic repulsion. When you try to press the north poles of two magnets together, you can feel the repulsion, which gets stronger as the two magnets get closer. That same kind of repulsion happens when trying to press the protons of two hydrogen atoms together.

One way to get hydrogen atoms to fuse into helium atoms is to use a nuclear bomb to generate the appropriate temperatures. A hydrogen bomb (also known as a fusion bomb) is a two stage weapon. The first stage is a traditional uranium-powered fission bomb that explodes toward a capsule containing tritium and deuterium (two forms of hydrogen). The tritium and deuterium fuse together to create helium. As helium is created, a huge amount of energy is released. As we see in the sun, that energy takes the form of heat and light. This second stage fusion reaction is what makes a hydrogen bomb so energetic.

Hydrogen bombs prove that fusion is possible, and very powerful.

However, they also show how messy the process can be. The goal of a fusion research is to tap into the power in a controlled way that eliminates the explosion.

One technology that is being used to contain the temperatures needed for fusion is called a tokamak. A tokamak looks like donut-shaped cavity surrounded by magnets. The magnets allow a ring of energetic hydrogen plasma to be created at the center of the hollow donut, so that the plasma does not touch the walls of the chamber. If the plasma is heated to 100+ million degrees Celsius, hydrogen atoms start fusing to create helium atoms. At that point, the heat of fusion keeps the plasma hot and the reaction becomes self-sustaining. The extra heat produced can be converted into electricity.

A second way to create a fusion reaction is to burn a little bit of fuel at a time. In this approach, powerful beams of laser light focus on a tiny capsule of hydrogen. Think pepper corn in size. The lasers provide the heat to initiate a fusion reaction, which then extinguishes itself because the amount of fuel is so small.

At this point in the research process, scientists are about to build a tokamak that may be large enough to contain a real self-sustaining reaction. It is called ITER. And scientists have built and are testing a laser facility that may demonstrate the principles needed to build an eventual power plant. It is called the National Ignition Facility. But these are huge endeavors that are extremely expensive, so the research process is slow and deliberate. It may be several more decades before a large, reliable fusion power plant design emerges from this research.

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