How Do You Contain A Material So Hot It Vaporizes Everything It Touches?

That question is one of the major challenges facing proponents of fusion energy. Fusion power generation attempts to mimic the processes occurring in center of stars by heating atoms to incredibly high temperatures and pressures such that they slam together with enough force to fuse, thereby releasing energy. The problem is that the temperature required to achieve such a reaction is on the order of 150 million degrees Celsius, ten times hotter than the center of the sun and a heat level that no material on Earth can withstand.

Fusion reactor inspiration: the sun. Image from NASA Goddard Laboratory for Atmospheres.Fusion reactor inspiration: the sun. Image from NASA Goddard Laboratory for Atmospheres.

Fusion energy, though currently unproven at a commercial scale, offers sufficient advantages to make ongoing investment worthwhile. Unlike traditional fossil fuels, it produces no greenhouse gases and has a virtually limitless fuel supply, and contrary to nuclear power it does not yield long-lived nuclear waste. Think fusion reactions are something out of the distant future? Think again; mankind is actually already quite good at their production. Maybe even too good: the hydrogen bomb is simply an uncontrolled fusion reaction. If we can only find a way to confine and manage the energy produced in the explosion, we will have an essentially limitless supply of clean energy. Therein lies the challenge.

The primary (though not sole) method of confining the superheated, ionized gas called plasma which leads to fusion reactions is through a device known as a tokamak. Traditionally, tokamaks are donut-shaped devices that use strong magnetic fields to confine the plasma, thereby ingeniously circumventing the problem of vaporization of the chamber walls. This technology is not at all the esoteric specialty of a few scientists, the tokamak-based International Thermonuclear Experimental Reactor (ITER) currently being built in France is positioned to be the first commercial scale nuclear fusion reactor and will require an investment of at least $18 billion from its international partners by the time of its completion in 2027.

Tokamak: these donut-shaped devices use magnetic fields to contain superheated plasma. Image by Abteilung Öffentlichkeitsarbeit at the Max-Planck Institut für Plasmaphysik.Tokamak: these donut-shaped devices use magnetic fields to contain superheated plasma. Image by Abteilung Öffentlichkeitsarbeit at the Max-Planck Institut für Plasmaphysik.

Tokamaks have been around since the 1950s when they were developed in Russia, and though they have advanced considerably in the decades since, one thing has remained relatively constant: their toroidal shape. Now, researchers are revealing that a spherical shape (picture something less like a donut and more like a cored apple) may allow tokamaks to be made smaller, cheaper, and faster. Given that ITER is expected to be 10 stories tall and the mass of three Eiffel Towers, this could be a considerable breakthrough.  Not to delve too far into the complex physics, the basic principle of the spherical device is that particles contained in such a tokamak will possess an unusual stability near the center of the sphere allowing them to be more easily confined.

Spherical tokamak: the spherical shape may allow easier particle confinement and thus smaller, more practical reactor. Image by the Culham Centre for Fusion Energy.Spherical tokamak: the spherical shape may allow easier particle confinement and thus smaller, more practical reactor. Image by the Culham Centre for Fusion Energy.

In the upcoming few years, spherical tokamaks will be tested in the several top laboratories in preparation for the next step: upscaling. Certain companies are already taking notice with the suggestion that these devices may be able to produce more power than they consume within the next decade, a timeline on par with ITER. While it may still be ten or more years before fusion reactors become a reality, one thing we’ve learned with this week’s reveal is that apples trump donuts in more areas than just healthcare.

Via Science.