Archive for the ‘fusion’ Category

Physicists “flip the D” in tokamak, get unexpectedly good result

March 20th, 2019
Image of a room with metallic tiles and a large central pillar.

Enlarge / "Small" isn't necessarily all that small when it comes to tokamaks like the DIII-D. (credit: Wikimedia Commons)

In the world of fusion physics, two letters say it all: ‘L’ and ‘H’. All the cool kids play with the H-mode, which is hot and fiery and is our best prospect for achieving useable fusion energy. The L-mode, which is neither hot nor fiery, has been largely abandoned. But by changing the shape of the L-mode, researchers have been able to get unexpectedly high pressures. High enough for fusion? Maybe.

To understand what all that means, we need a quick refresher on what a tokamak is.

We’ve covered fusion physics before, but in short, a tokamak reactor uses a series of twisted magnetic fields to confine a fluid of charged particles (called a plasma) in a donut shape. The temperature and pressure of the plasma is the key to fusion; once it's hot enough, the positively charged nuclei will collide to fuse, releasing gloriously large amounts of energy. 

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National Ignition Facility recreates the interior of heavy stars

August 7th, 2017

Enlarge (credit: Lawrence Livermore National Lab)

In a lot of ways, stars are our model for creating nuclear fusion here on Earth, with fusion power often promoted as “harnessing the power of the Sun.” For all that, however, we have some surprising gaps in our understanding of what’s going on inside stars. That’s partly because we must infer what’s going on there based on the elements and particles that reach the solar surface, and partly because finding ways to test our theoretical models of fusion reactions is so difficult.

So there’s a certain appealing symmetry about a paper that was released by Nature Physics today. In it, researchers describe using the National Ignition Facility, built to study fusion using a giant laser, as a model for the interior of heavy stars. The results show that, despite their limitations, our earlier efforts to understand stellar fusion were on the right track.

Cross checking the cross-section

On a simple level, most stars fuse hydrogen to form helium. But things are obviously more complex than that. Most of the hydrogen in our Sun is the lightest form, with just a single proton as its nucleus. The helium produced in stars has two protons and two neutrons. Obviously, making helium from only protons requires a series of nuclear reactions, each with distinct probabilities of occurring that depend in part on the conditions inside the star. Complicating matters further, there are some other possible reactions that don’t lead directly to helium but can still occur inside a star, producing things like heavier isotopes of hydrogen.

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Placing humans at center of computer optimization yields hot plasmas

July 30th, 2017

Enlarge / It looks like science. (credit: Tri Alpha Energy)

If there is one thing I hate, it’s optimization. Computers don’t actually understand what they are optimizing. And that creates problems for everything from bicycles to nuclear fusion.

The process goes something like this: you have a mathematical model of a bicycle. You want your bike to perform better, but there are so many things that can be changed, so you can’t imagine finding the best configuration on your own. So you write a script. The script will vary the configuration of the bicycle and evaluate whether it is improved. After many iterations, you have the perfect bike, right?

No, you don’t. What you didn’t imagine was that the computer would remove the seat. Or that it would place, for no apparent reason, a third wheel between the (now removed) saddle and handlebars. Even worse, the stupid machine has got the chain passing through a bit of solid steel.

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