Stellarators Back Online After Decades in the Dark

For the past 30 or so years, fusion research has been dominated by one reactor shape: the tokamak. Though it’s been the most reliable way to achieve stable magnetic confinement of plasma, the design may soon give some ground to the stellarator, an older and simpler reactor technology.

Set to go online in just over a year’s time, the $1.45B Wendelstein 7-X stellarator is a throwback to an earlier time in high-energy physics. Based on a design first created in the 1950s, the stellarator design fell out of favor with physicists due to the fact that computers of the day couldn’t calculate the complex geometries of the magnetic fields required to contain the machine’s stellar-hot plasma.

Essentially, all fusion reactors, whether they’re tokamaks or stellarators, are vessels designed to contain a superheated, plasmatic, atomic soup where hydrogen atoms fuse into helium. Since no known material can withstand such incredible energy levels, fusion researchers employ magnetic fields to confine this awesome energy state within a fixed boundary. Though that explanation sounds simple enough, getting the physics right for such a reactor takes amazing computing power and generations of PhDs.

Although stellarators demonstrated some successes in the 1950s and 60s, tokamaks eventually became a more popular and productive reactor design. In fact, much of our understanding of fusion ignition and sustainable energy generation has come from tokamak research. However, the tokamak has its own fatal flaw, the design makes its plasma field susceptible to instabilities that can stop an experiment dead in its tracks.

With today’s robust computer simulations it looks like the stellarator may make a comeback, with the Wendelstein 7-X as the design’s vanguard.

Containing 50 non-planar and 20 planar 3.5 meter tall superconducting magnetic coils, the Wendelstein 7-X is designed to produce plasma discharges lasting up to a half an hour. Housed in the Max-Planck-Institut für Plasmaphysik, the 7-X was designed to be an engineering test bed for future fusion reactors.

Even though the 7-X won’t ever house an actual fusion reaction, many of the technologies being built into the machine will offer the designers of future tokamaks and stellarators greater insight. One such experimental system, which will be critical to the function of the 7-X and future iterations, is the reactor’s super-cooled, super-conducting magnets. Held at -269 °C, the control and engineering of the cryogenic field generator is itself quite an undertaking.

Although construction is well underway for the world’s largest tokamak at ITER’s facility in France, the Wendelstein 7-X (and stellarators in general) could still have a dramatic impact on fusion research. Given the project’s relatively small price and the fact that it is less complex than a traditional tokamak, Wendelstein might prove that stellarators still have a say in the pursuit of net-gain fusion reaction.

Image and Video Courtesy of Wikipedia, NDR & Plasmaphysik