Wendelstein 7

Perched loftily on Germany's Baltic coast, the small-to-middling town of Greifswald continues to be at the forefront of research into nuclear fusion. This is in no small part down to the presence of the Wendelstein 7-X – a fusion reactor so complicated they literally needed a supercomputer to design it. The latest tidings from the Max Planck Institute for Plasma Physics, creators of the Wendelstein 7-X, are that a new record has been set for the so-called fusion product. This is a theoretical performance benchmark rather than physical matter, but all the same, it's another significant step along the path to practical fusion power.

The fusion product is a measure which indicates how close a reactor is to plasma ignition – the critical point at which nuclear fusion becomes self-sustaining, and which happens naturally in stars like our Sun at a mere 15 million degrees Celsius (or 27 million degrees Fahrenheit, if that helps you compare things to a balmy summer's day.) The product is the result of multiplying ion temperature and density, then dividing by time and hence measured in degree-seconds per cubic meter. This latest hoopla is all because Wendelstein 7-X has achieved 10 to the 26th power of those, which is really rather a lot, apparently.

"This is an excellent value for a device of this size, achieved, moreover, under realistic conditions, i.e. at a high temperature of the plasma ions," Professor Sunn Pedersen says in a press release.

This is all down to the graphite tiles, new as of September 2017, which let the reactor reach higher temperatures and longer plasma discharges. These have had to have been made to work with the complex stellerator design. This was first conceived by Lyman Spitzer at Princeton in 1951, but proved too complex to manufacture till the rise of the supercomputer. The tiles have to follow the path of the plasma edge which is most likely to interact with the containing vessel.

"This makes us optimistic for our further work," Pedersen concludes anticlimactically.

In concurrent good news, analysis of experimental data from 2015 and 2016 now published in Nature Physicssuggests that the team has succeeded in minimizing what is known as bootstrap current: residual electricity induced by pressure variations in the plasma which could distort the very magnetic field keeping said plasma in check. It being so problematic, it's almost tempting to wonder why they don't do without the plasma altogether – until one remembers the plasma (made up of the hydrogen isotopes deuterium and tritium) is where the all-important fusion actually takes place. Best keep it, then.

"More exact and systematic evaluation will ensue in further experiments at much higher heating power and higher plasma pressure," lead author Andreas Dinklage said in a press release, though the quote reads better if you imagine him letting off a party popper between "heating" and "power."

We've watched progress at the Wendelstein 7-X with great interest over the years, from its first helium and hydrogen plasma discharges to these latest developments today. We'll keep you posted.

Source: Max Planck Institute

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