Star in a Bottle

by Tomas Gonda

In the 1950s the Atomic Energy Commission promised Americans that energy would soon be “too cheap to meter.” The AEC was referring to the prospect of nuclear energy, specifically nuclear fusion energy. Notably, it has been a bit longer than “soon” since the 1950s and my electricity bill is still quite a bit higher than $0. This birthed the joke that nuclear fusion is 20 years away and has been for the last 70 years. So, what is fusion and is this joke still valid?

Nuclear energy works by exploiting the stability of atoms. In the center of each atom lies several protons and neutrons, or positively charged and uncharged particles, in the nucleus. But that begs one to question how atoms even stay together. If the same sides of two magnets repel each other and the same is true for charged particles, what explains the stability of an atom? Conveniently there is a very strong force that only works on the scale of the nucleus of atoms that bind these positive charges together and as a result, a bunch of notoriously creative physicists decided to call this the “strong force.” Depending on how many protons and neutrons that an atom has, it will require more or less of this strong force to keep it together. One may think of the atoms as being, more or less, “comfortable”. An atom with many protons and neutrons, for example uranium, is very uncomfortable (it needs a large strong force) and if it is prodded enough, it can split into two smaller more comfortable atoms that require less total strong force combined than the initial uranium atom. Nature, in its mysterious perfection, only uses the exact amount of strong force that is necessary and then the leftover is released. This process is called nuclear fission or splitting and the excess energy that is released is what we call nuclear energy. This energy release can be controlled, like in a power plant, or uncontrolled, like in a nuclear bomb. There are reasonable public concerns about the controlled fission process due to several horrific nuclear catastrophes that have occurred in the past, yet overall, fission safety is much more comparable with solar and wind than coal and gas.

On the other side of the coin is nuclear fusion. Instead of splitting a large atom, which occurs in nuclear fission, two smaller atoms (specifically the nuclei) are brought together and fused into a larger one. The nuclear fusion process is what powers all of the stars in the universe and it is the most efficient method of energy generation known to humankind. You could even go so far as to say that it is the universe’s method of choice. At a glance, fusion is fantastic. As fuel it uses hydrogen, of which there is billions of years’ worth in our seawater, it exhausts helium, of which we have a non-renewable supply, and it emits no greenhouse gas. The radioactive waste from nuclear fusion is only dangerous or “hot” for less than 100 years, whereas fission waste is hot up to 100,000 years. Moreover, the technology is already established such that fusion energy can plug directly in to and supply our current power grid as well as be modulated for variable energy demands. Therefore, nuclear fusion excels against all potential energy sources in obtainability, sustainability, dispatchability, and risk.

The quest of a fusion physicist is to replicate the conditions of the interior of the sun here on Earth. In other words, to put a star in a bottle. This is done by heating hydrogen until it enters the plasma state, which is like a gas except the electrons have been separated from the nucleus of the atom. The sun is an example of a plasma. Each particle in a gaseous plasma is charged and so it attracts or repels every other particle. This is where the challenges begin for fusion physicists. To force the nuclei together so they can fuse, the plasma is confined in a cylindrical magnetic field. The cylinder is then twisted around into a donut shape so the particles can go around forever. Think of forming a donut of Jell-O (the plasma) using only rubber bands (the magnetic field). Using fancy microwaves and many magnets, fusion scientists try to get more energy out of the machine than the input energy used to heat the plasma. This feat, named “breakeven,” has still not yet been achieved. Auburn’s plasma physics group employs our university’s Compact Toroidal Hybrid (CTH), a fusion-research device too small to do fusion, but large enough to help us learn how to achieve breakeven. CTH is involved in various supporting research tasks to help larger collaborations like DIII-D, Wendelstein 7-X, and ITER. Currently being constructed in southern France, ITER is due to be operational in 2025 and, when complete, will be the most expensive science experiment ever. As a proof of concept, by 2035 ITER aims to have 10x breakeven energy output, with power plants planned to be operational soon after. This is a massive international collaboration to achieve fusion and Auburn University is playing a role in this endeavor. The joke is no longer valid, fusion energy is 20 years away, for real.

Disclaimer: The views and opinions in this work are those of the author and do not necessarily reflect the views of Auburn University.