It’s 2015. Where’s My Mr. Fusion?

Most of us who grew up in the 1980s remember the science fiction comedy movie Back to the Future, starring Michael J. Fox and Christopher Lloyd. In one scene, Lloyd’s character returns to 1985 from the year 2015. He grabs a banana peel and a beer can from a garbage pail and stuffs them into a futuristic piece of equipment called Mr. Fusion (which looks suspiciously like a Krups coffee grinder). This device generates the power necessary for his time machine.

The idea that clean and plentiful fusion energy was just around the corner also appeared in another time travel-themed 1980s science fiction movie. In the 1986 film Star Trek IV: The Voyage Home, Mr. Spock mentions that there was a “dubious flirtation” with nuclear fission in the late 20th century, but that it became obsolete “by the beginning of the fusion era.”

Well, here we are in the year 2015. A quick look out the window confirms that flying cars and levitating skateboards, while they actually exist, are still not commonplace. We don’t have transparent aluminum yet, either, although we do have aluminum oxynitride, a transparent ceramic that includes aluminum in its chemical composition. What are the prospects for nuclear fusion power?

Nuclear fusion is a reaction in which the nuclei of two atoms combine to form the nucleus of a new atom. This reaction generates a tremendous amount of energy; in fact, it’s what fuels the sun and other stars. Unlike the process used in today’s nuclear power plants, nuclear fusion doesn’t require radioactive fuel, and doesn’t produce long-lived radioactive waste. However, it doesn’t occur readily under normal Earth conditions.

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All atomic nuclei have a positive electric charge. Since like charges repel each other, there is an electrostatic repulsive force that keeps the nuclei apart. But if two nuclei manage to get extremely close to each other, another force takes over: the nuclear force. This is the same force that holds positively charged protons and zero-charge neutrons together within each atomic nucleus. Over very short distances, the attractive nuclear force is stronger than the repulsive electrostatic force. This brings the two nuclei together, resulting in a release of energy.

In all gases, liquids, and solids, atomic nuclei are surrounded by negatively charged electrons. Electrostatic repulsion between electrons keeps the nuclei from getting anywhere near close enough for fusion to occur. However, in a state of matter known as plasma, positively charged nuclei and negatively charged electrons are not bound to one another. Nuclear fusion can occur in very high-temperature plasmas (tens of millions of degrees).

The extremely hot plasma must be confined in some way. In stars, the plasma is confined by the enormous gravitational forces produced by the star's mass. This is impossible on Earth, which is thousands of times less massive than even the smallest stars. Instead, in a type of fusion reactor known as a tokamak, the plasma is confined by powerful magnetic fields. Alternatively, in an approach known as inertial confinement fusion (ICF), high-energy lasers are used to rapidly heat and compress fuel pellets.

Both approaches are being pursued. The world’s largest tokamak project is the International Thermonuclear Experimental Reactor (ITER), currently under construction in southern France. The project had its genesis at a 1985 summit between the US and the Soviet Union. Today, the international team includes the US, Russia, China, India, Japan, South Korea, and the European Union.