The Radical Promise of Nuclear Fusion

The artificial intelligence boom has sent Silicon Valley scrambling for energy. The data centers necessary to train AI models and run their applications require massive amounts of electricity. In order to get all of the energy they need—and reduce their toll on the environment—big tech companies such as Amazon, Google, and Microsoft have recently started striking deals for nuclear energy—a so-called “clean” energy source because it doesn’t emit significant amounts of carbon into the atmosphere. In that spirit, we thought it was high time to republish a critical essay by Anna-Sofia Lesiv about the promise of nuclear fusion and the path the U.S. took to get there.—Kate Lee 

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On December 5, 2022, we learned that fusion was possible on Earth.

The Lawrence Livermore Laboratory’s National Ignition Facility (NIF) lies about 50 miles east of San Francisco. A multibillion-dollar undertaking of the U.S. Department of Energy, the NIF is the largest and most powerful laser on Earth. Actually, it’s not just one laser—it’s 192 lasers lined up next to one another, spanning the length of two football fields. The light from these lasers is accelerated and amplified six times before being converted into ultraviolet light and targeted precisely onto a metal cavity that contains a tiny capsule filled with hydrogen isotopes. The lasers are shot at the capsule for a billionth of a second and produce a temperature 10 times hotter than that of the Sun’s center.

At about 100 million degrees Celsius, hydrogen isotopes are colliding into each other with such immense speed that they begin to fuse. As they do, they release a blast of energy so powerful it pushes other hydrogen isotopes to fuse until all the fuel in the capsule is used up. 

This process of heating up the capsule to the point that all its fuel is consumed in a fusion reaction is called ignition. The concept is nearly equivalent to the act of producing enough friction to light a match. It sounds simple enough, but it has taken decades, billions of dollars, and hundreds of attempts to get right. For years, the NIF’s failed attempts led to it being ridiculed as the “Never Ignition Facility” or the “Nearly Ignition Facility,” so you can imagine the relief that ensued when the then 13-year-old, $3.5 billion laser system finally managed to light fusion’s match. Upon hearing the news, Tammy Ma, who heads the fusion initiative and had worked at the Lawrence Livermore lab for over 14 years, burst into tears while waiting to board a plane.

Ultimately, the NIF laser beamed 2.05 megajoules of ultraviolet light at the fuel capsule, inducing a fusion reaction that released 3.15 megajoules of energy.

Three-point-one-five megajoules is not even one percent of what a nuclear power plant produces every hour. In fact, it’s just about the amount of energy required to boil two pots of water. However, the NIF was not built to be a functioning power plant; it was built as a laboratory experiment with the explicit purpose of achieving fusion ignition. That effort was a resounding success, and it has placed the coveted milestone of achieving ignition into our rearview mirror once and for all.

The coming challenge for the scientific community devoted to making fusion power a reality now lies in figuring out how to scale this process to an industrial level. Achieving feasible fusion power is a massive design problem that currently presents more questions than answers.

Luckily, tracing the history of fusion technology can introduce us to the main concepts, bottlenecks, and opportunities scientists and entrepreneurs will be wrestling with to finally unlock star power on Earth.

The astonishing discovery of fusion

The secret behind the Sun’s endless power was a deep, cosmic mystery for a long time. Ironically, it was a quest into the nature of the very small that unlocked insights into the very big.

In 1919, Francis Aston, a precocious British chemist, was determined to measure the weight of an atom. It was just a year after the end of the First World War, for which he had enlisted in the army servicing some of Britain’s earliest air force fleet. The war had thwarted his desire to burrow away in a lab and focus exclusively on research, and he returned to Cambridge to conduct his experiments in peace.

The early 20th century was an exciting time in chemistry. There was a firm understanding that all matter was composed of elements—particles of an essential nature, which could not be transformed from their fundamental state. Centuries of discovering solid elements like metals, and distilling various liquids and gasses, resulted in humanity collecting a list of such fundamental elements—gold, silver, sodium, oxygen, and hydrogen. Various forms of chemical analysis helped establish the approximate relative weights between the elements, which allowed Dmitry Mendeleev to organize them according to their mass in a table—today’s periodic table.

At the time, the properties of elements and their relationships were understood only approximately, but Aston was not satisfied with approximation. He wanted to measure the precise weights of the atoms themselves.

His method was a clever trick, analogous to determining someone’s height by measuring their shadow. He figured that if he could run ionized atoms through a magnet that deflected the path of their flow, he could determine the weight of ions by the amount the magnet deflected them. The lightest atoms were easiest to deflect, and the heavier atoms were the hardest.

The device created to enable this measurement is known as a mass spectrometer, and it revealed something weird about the weights of the individual atoms. Aston found that the elements were not perfect multiples of hydrogen’s weight; they always weighed slightly less than a perfect multiple of hydrogen. For example, helium wasn’t four times the weight of a hydrogen atom—it was actually 3.97 times its weight. This discrepancy carried a clue. 

The results of Aston’s experiments caught the attention of an astronomer and physicist named Arthur Eddington. Years before, Eddington had read Albert Einstein’s 1905 paper, which claimed that there was an equivalence between mass and energy: E=mc^2. The mystery of the missing mass could mean only one thing in Eddington’s mind: the conversion of mass into energy. Eddington was preoccupied with thoughts of stars, planets, and galaxies, and this insight from a chemist opened his eyes to the mechanism that makes the Sun shine.