Ignition by nuclear fusion has been obtained for the first time this month at the National Ignition Facility (NIF) of Lawrence Livermore National Laboratory, but why is this event so important? This historic first ignition demonstrates that we can create a controlled fusion in the laboratory that it releases more energy than we put in, and while the road to a commercial-grade nuclear fusion power plant is a long one, that’s a huge milestone, and as some people have described it, now we understand the physics, it’s just an engineering problem.
That we have the reduced physics is mostly correct, but there is still room for refinement and the engineering part is certainly the crucial hurdle. The event reached Q = 1.54, but what does that mean? To get the exact amount of energy you input you should have Q = 1, whereas in this case they got the 54 percent more; several online users however said that a realistic goal for a commercial grade nuclear fusion reactor would be something closer to Q = 10.
How does fusion work in stars?
Nuclear fusion is what powers the Sun and all the stars in the Universe. Under the enormous pressure and heat within the stars, the lighter nuclei are pushed together, overcoming their electromagnetic repulsion, and fused into a heavier nucleus, this process releasing a lot of energy simply because the energy-to-mass ratio of the original elements is greater than the products, while the difference is the energy that is released.
So, for example, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium every second, where hydrogen is the easiest element to fuse, having only one proton in its nucleus, and as it the elements get heavier with more and more of these positively charged particles, you get less and less energy. You can’t smelt something heavier than iron and expect to get energy.
Lab fusion works on the same principles but with some important differences: first of all, we are not building an entire Sun. The amount of molten hydrogen is relatively small and requires much higher temperatures, since the pressure in these reactors is categorically different from that at the center of the stars.
How is nuclear fusion achieved in the laboratory?
Scientists have come up with several reactor designs to do the same thing: push hydrogen atoms together, though it’s not ordinary hydrogen that’s made up of just one proton in its core. They often use two isotopes of hydrogen which have extra neutrons in the nucleus i.e. deuterium which has one neutron and tritium has two, however lithium is also another possible element used in some designs.
Whatever the elements, the goal of the fusion reaction is to release energy and high-speed neutrons, the latter being essential for energy extraction. These particles will hit the containment walls, heating them, after which that heat can then be used to heat a fluid that is then used to drive turbines.
The main projects (but there are many different ones) use the inertial confinement (ICF) by laser which has just shown its success at the NIF, tokamak and stellarator. The NIF project sees a heavy hydrogen pellet placed in a tiny cylinder. This container is hit with the world’s largest laser and vaporized in an instant. As it turns to plasma, it shoots inward, where it meets hydrogen (or other nuclear fuel) with such force that the fuel is compressed and melts.
The tokamak and stellarator approach instead confines the hydrogen plasma inside a magnetic field and is heated to incredible temperatures, much hotter than the center of the Sun, and so far, these approaches have not achieved ignition, therefore energy produced in the plasma is not sufficient to keep the plasma hot. A full-scale tokamak reactor called ITER is currently under construction in the south of France, which should hopefully prove it.
But does a fusion power plant produce clean and, at the same time, safe energy? One of the main claims of the nuclear fusion is that it is safe and clean, and to a large extent, that is true. A fully operational nuclear fusion power plant would not risk a nuclear meltdown, in the unfortunate event that something goes wrong, the plasma cools down and stops being plasma, moreover it does not emit carbon dioxide, however it produces nuclear waste, but simply because the neutrons emitted make the material that absorbs them radioactivehowever the amount of this material it is tiny compared to the high-level nuclear waste produced in nuclear fission power plants.
The fuels used tend to be abundant in nature, but it also depends on how they are extracted from the environment. There are also concerns about how fusion energy technology could be used for military purposes since nuclear fusion can produce tritium, used in hydrogen bombs, or more quickly and efficiently produce weapons-grade plutonium or uranium, so how technology goes, it has the potential to be clean and safe, but ultimately it depends on how we approach it.
Nuclear fusion research has achieved some major milestones in recent years, and it looks like the old joke that nuclear fusion is always a couple of decades away may soon prove to be true.
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