An X-Ray of Hope for Future of Fusion
The scramble for funds and strong disagreements over which nuclear fusion technology shows the most promise have left the scientific community splintered by bitter rivalries.
The goal of producing electricity through nuclear fusion, and thus providing the world with a virtually limitless source of energy, has proved to be staggeringly difficult, and many experts contend we are not a lot closer today than we were 40 years ago.
The frustration among techno-wizards has spread to politicians, leading Congress to slash a wide range of projects aimed at harnessing the energy that powers the sun. It all came to a head last year when Congress pulled the plug on funding for U.S. participation in the $10-billion International Thermonuclear Experimental Reactor, all but wiping out that troubled project even before supporters could decide where to build it.
That being the case, why would anyone want to venture into that arena today?
Scientists at Sandia National Laboratory in Albuquerque think they’ve found a better way to deal with the problem.
They are betting that an old workhorse designed for military purposes might lead the way into the age of fusion. Just four years ago, the lab’s “Z” machine, the most powerful X-ray source on the planet, had been scheduled for the trash heap because it had already served its purpose.
But now it has emerged as a dark horse--very dark, some say--in the sluggish race to produce electricity with fusion reactors.
Here, in a nutshell, is what they think might do the trick.
*
If you could set off a tiny fusion explosion every second and capture the heat from each blast to generate steam to run a turbine, you would have yourself a fusion power plant. Of course, every time you set off one of those explosions it’s going to damage some of your equipment, so it will be necessary to have a continuous flow of new parts to keep the system running.
Lab experts insist it’s not as farfetched as it sounds.
The concept grew out of discussions at the lab about the future of fusion research. The scientists began asking what they could do to achieve fusion with today’s technology, rather than waiting for new technologies that may take decades to develop.
“We wanted to know, what’s the most you could do with today’s technology to build a reactor?” said Mark Derzon, a nuclear engineer at Sandia with 20 years’ experience in fusion research.
They figured the Z machine was a good place to start. The machine, designed to study the effects of intense radiation, is indeed a marvel. Using regular household electricity, the machine charges a bank of capacitors, which are like large batteries that can discharge all their energy instantaneously.
The juice comes out in 100-billionths of a second, resulting in a 290-trillion-watt pulse. That’s about 80 times the entire world’s output of electricity, but it only lasts a few billionths of a second.
Research indicated that such a powerful pulse striking a pea-sized pellet of deuterium-tritium could cause a fusion reaction--if a number of other complex parameters were also met. But the reaction would have to be repeated about once a second to provide a continuous flow of heat, and that’s the rub.
The explosion would wipe out the cables used to carry the electric current into the chamber, and pretty much make a mess out of everything. The chamber would have to be “pumped” out to reestablish the vacuum needed for the next explosion, and the cables would have to be replaced in time for the next blast a second later.
*
Derzon and several colleagues figured out a way to get around pumping out the entire chamber each time. Only the area between the contact points on the two electrical cables would have to be cleaned.
As for replacing the cables, Derzon came up with an idea that is “startling in its simplicity,” said one lab source.
The reactor consists of two main components, including a radiation chamber where the explosion takes place. A cap on the chamber is equipped with electrical cables, or conductors, which carry the pulse to the target. Think of it as sort of like a garbage can with a replaceable lid.
In the Sandia reactor, the chamber would remain stationary, but the lids would move along a carousel. Electricity flows through the cables in the lid, striking the target--and bingo, you’ve got fusion. A plunger pushes the waste products, which can be used to make new cables, out the bottom of the chamber and the expended lid is quickly replaced by another. It would, Derzon admits, take a lot of lids.
Lab officials say they are confident it could work, and they have applied for federal funding to try it. But the carousel, if it works at all, solves only one of many problems, none of which is unique to the Sandia project.
The lab’s Gerold Yonas, an expert on space-based defense systems, has said he believes it will be necessary to achieve temperatures of 3 million degrees inside the radiation chamber for fusion to occur.
The Z may not be up to that, but Derzon said it came close just last August.
In addition, the electricity must be delivered in exactly the right form--called a pulse shape--for fusion to occur. Derzon said progress has been made there as well.
*
But that brings us to what many regard as the most difficult problem facing any fusion program: perfect symmetry.
For fusion to occur, the fuel must be compressed uniformly in all directions. In a hydrogen bomb, that is achieved with the help of an atomic bomb, which serves as the trigger. The A-bomb surrounds the hydrogen fuel, and when it goes off it causes the fuel to compress in perfect symmetry, thus facilitating the fusion reaction.
In experimental fusion reactors, that is achieved most commonly by a magnetic field that serves as a “bottle” to hold the fuel that gets so hot it would melt anything else.
It is not clear yet how the Sandia researchers plan to attack that problem. So there are still hurdles.
“I don’t want to leave you with the thought that we know how to do this,” he said. “What we are hoping is that a concept like this might bring it closer.”
Lee Dye can be reached at leedye@ptialaska.net.
