The Problem With Fusion
Why haven't we unlocked the ultimate energy source yet?
In December last year, the National Ignition Facility (NIF) reached a scientific milestone many thought was impossible to reach for decades. They were able to create a net gain in energy from a nuclear fusion reaction, meaning that they were able to receive more energy from a reactor than they originally inserted. This monumental achievement will allow us to replicate the process that powers stars and, in turn, unlock the ultimate clean energy source. But recent experiments at NIF have failed to get anywhere close to last year’s record-breaking experiment. So, why is there no progress? Is fusion technology stagnating? Or is something else going on?
Before we dive into the problems facing NIF and all fusion experiments, let’s first recap what fusion is and what NIF is.
Nuclear fusion is the process that keeps the Sun “burning.” The Sun is made of mostly hydrogen, and at its core, the temperature and pressure are so high that the collisions between hydrogen atoms have enough kinetic energy to overcome the repulsive forces that keep atoms separate. These collisions cause the two hydrogen atoms to fuse together into a single, larger helium atom, but a helium atom is slightly lighter than two hydrogen atoms, given that it needs fewer gluons in its nucleus. This excess mass is turned into energy and released. As Einstein stated in his famous E=MC² equation, a small amount of mass is equal to a vast amount of energy. This means that a single fusion reaction releases an unholy amount of power through radiation and heat.
Fusion is so potent that fusing 17 tonnes of hydrogen will release enough energy to power the entire US for a year! That equates to only 0.05 grammes of hydrogen per US citizen! Even better, helium is the only gas emitted throughout this process. This incredible fuel efficiency and zero carbon emissions make fusion power one of the most eco-friendly energy sources on Earth.
For decades, scientists and engineers have tried to figure out how to replicate and harness this process to create tremendous amounts of incredibly clean energy. This has led to a plethora of different fusion reactor designs that use different methods, such as magnetism, inertia, and even raw kinetic energy, to create fusion. However, these methods all required significantly more energy to be inputted than was outputted from the fusion reactions, and many scientists thought it would be decades before we broke this energy net-loss barrier.
So how did NIF breakthrough?
Well, NIF is an inertial fusion reactor. It fires an incredibly powerful laser at a hydrogen-containing pellet housed in a golden tubular container. The laser vaporises the hydrogen astonishingly quickly, turning it into an incredibly hot and dense plasma. This super-heated hydrogen emits a large amount of X-rays, which are reflected by the golden container, and these reflected rays compress the hydrogen even further. Then, the temperature and pressure of the hydrogen plasma skyrocket, and fusion begins.
By finetuning the pellet design and golden housing, as well as introducing strong magnetic fields to further compress the plasma, NIF can reach efficiencies that no other fusion experiment can match. This means that, as the fusion process starts to happen, the energy it emits is retained within the plasma, heating it further and causing more fusion. This self-propelled burning is known as “ignition,” and it dramatically increases the energy yield of a fusion reaction.
On December 5th, 2022, NIF managed to reach ignition. Their 2.05 MJ laser kickstarted a fusion reaction that emitted 3.15 MJ of energy, giving a net gain of energy of 54%! Note here that numbers here refer to “energy in ” and ”energy out” of the reaction, not the reactor. The laser NIF uses is only 0.5% efficient, and energy capture systems typically only reach around 60% efficiency. So even with this milestone, we can’t turn NIF into a practical fusion power plant.
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