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WX-7: Plasma Power Ahead?

By Bill Moore

German scientists just may have taken the next important step to taping the power of the sun to produce energy here on Earth using nuclear fusion through the Wendelstein stellarator.

80 million degrees C! That's hot.

That's also the estimated temperature the world's largest stellarator achieved for one-quarter of a second on February 3, 2016 in Greifswald, Germany. It's so hot, in fact, that the only way scientists could actually measure it was to take X-rays images and calculate the temperature from the glow on the film.

German Chancellor Angela Merkel pressed the start button on the 5.5 m twisted donut plasma reactor known as Wendelstein 7-X. Despite the blink-of-an-eye burst of 2-megawatts of energy said to be equivalent to 6,000 microwave ovens, the scientific community is hailing the experiment a historic event. For the first time man has created a hydrogen plasma, a snap shot of which was just released by the Max Planck Institute and featured below.

X-ray image of hydrogen plasma created in one-quarter of a second and estimated at 80,000 degrees C.

The €400 million ($435m) project took some 9 years to build, although the concept of confining plasma, a super-heated gas stripped of its electrons, in a twisted torus has been around since the 1950s. Plasma is what makes fluorescent bulbs glow. A competitor to the Russian tokamak, which also uses magnetic fields to confine the super-heated plasma, the German machine made up of oddly shaped, super-conducting magnets, is believed to be easier to run, though extremely difficult to build. Mechanical tolerances must be controlled with the precision of a Swiss watch despite the fifty 11.5 ft (3.5m) tall electromagnets used to confine the plasma alone weighting some 425 tonnes (468 tons). Each is bathed in liquid nitrogen to keep them cool and get them to superconducting temperatures.

The goal of the project is to replicate here on earth, in a sustainable way, the fusion process that powers stars, the ultimate aim being to eventually replace fossil fuels and even nuclear fission. While fusion does generate some radioactive by-products, the most dangerous being tritium, their half-life is much shorter than fissionable waste, some measured in a few decades. In the case of tritium, instead of lasting tens of thousands of years, in 500 years it would be no more radioactive than coal ash, scientists say.

The Wendelstein machine isn't designed to produce power. It is intended to better understand how to confine and control hydrogen plasma, which as it fuses creates helium, a non-toxic gas used in party balloons and Super Bowl blimps. However, an energy-producing fusion reactor is still thought to be decades away. The best the German researchers hope for with their device is a sustainable operation of 30 minutes. A practical fusion reactor would have to reliably operate around the clock for years just to repay its enormous upfront investment.

In reading up on the WX-7 breakthrough, one very obvious question never seems to be addressed: what do you do with 80-to-100 million degrees Celsius? That's even hotter than the core of the Sun, which we think burns at some 15° million C. Even the surface of the Sun runs at a relatively cool (5,505° C/ 9,941° F). Do fusion power plant operators of the future somehow safely siphon off some of the unimaginable heat to boil water (which only requires 100° C (212° F) or molten salt to spin relatively crude electromechanical turbine generators? Presumably, a successful stellarator reactor would produce more energy than it consumes, otherwise it wouldn't make economic sense to build, much less operator.

Figuring out how to make effective use of that super-hot plasma may be just as daunting an engineering challenge in the coming decade as creating and sustaining nuclear fusion, itself.

Illustration of WX-7 Stellarator

Times Article Viewed: 2074
Originally published: 05 Feb 2016

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