Scientists image the sea monster of nuclear fusion: the Rayleigh-Taylor instability

Nov 12, 2010
This is an optical photograph of an aluminum z-pinch target tube installed in the Z machine.

(PhysOrg.com) -- A new X-ray imaging capability has taken pictures of a critical instability at the heart of Sandia's huge Z accelerator. The effort may help remove a major impediment in the worldwide, multidecade, multibillion dollar effort to harness nuclear fusion to generate electrical power from sea water.

"These are the first controlled measurements of the growth of magneto-Rayleigh-Taylor [MRT] instabilities" in fast Z-pinches, said project lead Daniel Sinars.

MRT instabilities are spoilers that arise wherever electromagnetic forces are used to contract (pinch) a plasma, which is essentially a cloud of . The pinch method is the basis of the operation of Z, a dark-horse contender in the fusion race.

A pinch contracts plasma so suddenly and tightly that isotopes available from sea water, placed in a capsule within the plasma, should fuse.

That’s the intent. Instead, the instability rapidly crimps the cylindrically contracting plasma until it resembles a string of sausages, or shreds the into more fantastic, equally useless shapes. This damaged contraction loses the perfect symmetry of forces necessary to fuse the material.

Fast pinches at Z, which take place in less than 100 nanoseconds, already have produced some neutrons, a proof of fusion. But a major reason not enough neutrons have been produced to provide a source of peacetime is the MRT instability.

Sinars led seven experimental shots to map the disturbance. The experiments were motivated by a concept proposed last year by Sandia researcher Steve Slutz.

Traditionally, scientists would use an array of spidery wires to create a compressed, X-ray-generating ion cloud. The X-rays were then used to compress fusion fuel.

Slutz suggested that the magnetic pinching forces could be used to directly fuse fuel by compressing a solid aluminum liner around fusion material preheated by a laser.

Because the new concept would not produce as a heating tool but instead relied on directly compressing the fuel with magnetic pressure, the MRT instability was the primary threat to the concept.

The top image is an X-ray (6.151 keV) photograph of the same target (see photo above) compressed by electromagnetic forces. The sequence of images below is cropped to show both outside edges of a cylinder from a camera's point of view as they distort over time in the grip of the MRT instability. Some of the jet-like features are approximately 50 microns, smaller in diameter than a human hair.

“Once we started looking at solid liners it was easy to conceive of doing a controlled experiment to study the growth of the instability,” Sinars said.

This is because experimenters could etch the solid tubes, creating instabilities to whatever degree they desired. Accurate etching is not an option with fragile wire arrays.

The MRT problem occurs because even minute dips in a current-carrying surface — imperfections merely 10 nanometers in amplitude — can grow exponentially in amplitude to millimeter scales. In the experiments by Sinars and others, the tubes were scored with a sinusoidal perturbation to intentionally start this process.

“The series of pictures over a time scale of 100 nanoseconds brought the life of the MRT into focus,” Sinars said.

Previously, competing computer simulation programs had given conflicting predictions as to the extent of the threat posed by the MRT instability, leaving researchers in the position, says Sinars, of “a man with two watches: he never really knows what time it is.”

The more accurate simulations will enable researchers to better tweak the conditions of future Z firings, more effectively combating the effect of the instability.

Researchers believe that with thick liners and control of the MRT, the Z machine could achieve an output of 100 kilojoules to match the 100 kilojoules input to the fuel to start the fusion reaction. “That would be scientific breakeven,” Sinars said. “No one has achieved that.”

That day, he says, may be just two to three years away.

The work is reported in a paper in the Oct. 29 issue of Physical Review Letters.

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Jarek
1.3 / 5 (4) Nov 12, 2010
(...)instability rapidly crimps the cylindrically contracting plasma until it resembles a string of sausages(...)

Sounds connected with flux ropes from sun's corona...
http://www.physor...sun.html
genastropsychicallst
1 / 5 (12) Nov 12, 2010
From ion(s)traight-up break of horizonta(l)-boson, those seadowns looks like A-Z but is not the source. To be read on my website,
El_Nose
3.3 / 5 (3) Nov 12, 2010
I wonder what running two fields slightly misaligned would do. like coherence and decoherence, might provide the smooth plasma containment necessary. -- but who cares about the ramblings of a non phyics major, with no proof to back it up. -- But i am curious.
A_Paradox
4.7 / 5 (3) Nov 12, 2010
that day, he says, may be just two to three years away.


Well! There's brave for you! Normally with nuclear fusion optimists it's "about 25 years away"
El_Nose
not rated yet Nov 12, 2010
question to physicists

isn't this actually Plateau-Rayleigh instability -- or just Rayleigh instability. Rayleigh instability is charaterised by dealing with a column of water and how surface tension breaks the column into droplets of the same volume and less surface area. effectively pinching the liquid into sausage like designs that with gravity produce droplets

Rayleigh-Taylor instability deals with two fluids of different density and the less dense fluid exerting force on the denser fluid.

??? did the author mess up here or am I way off my rocker??
ekim
3.5 / 5 (2) Nov 12, 2010
Well! There's brave for you! Normally with nuclear fusion optimists it's "about 25 years away"

http://www.genera...ign.html
This reactor is four years away. A decade to commercialization. Also no aluminum cans to crush and no degrading of reactor walls due to neutrons. Most reactor designs such as Z-machines ,Tokamaks and Pollywells haven't figured out how to achieve fusion with out damaging the reactor.
Neurons_At_Work
5 / 5 (6) Nov 12, 2010
From ion(s)traight-up break of horizonta(l)-boson, those seadowns looks like A-Z but is not the source. To be read on my website,

I have to admit, it's pretty cool to have a computer program that can string together random words and phrases like this, and then force normally intelligent readers to waste ten seconds of their lives allowing the resulting jargon to impinge on their collective retinas and chaotically fire disconnected nerve cells. Neat.
Husky
not rated yet Nov 12, 2010
i would think that solid liners is a good avenue, even if they can't fully overcome the instabillity, but still get within close range, adding an external X-ray laser or wire cage to augment the process and provide the minimal extra push needed might be the ticket. An external X-ray source would be interesting as it decouples the X-rays from the pinchflux itselve, effectively you could extend compression/fusion time by firing the x-rays with a slight delay after the solid liner has already collapsed
Newbeak
4 / 5 (1) Nov 13, 2010
Well! There's brave for you! Normally with nuclear fusion optimists it's "about 25 years away"

http://www.genera...ign.html
This reactor is four years away. A decade to commercialization. Also no aluminum cans to crush and no degrading of reactor walls due to neutrons. Most reactor designs such as Z-machines ,Tokamaks and Pollywells haven't figured out how to achieve fusion with out damaging the reactor.

Heard about this quite some time ago-I hope it pans out.One comment pertaining to the website: They say helium can be safely vented to the atmosphere.I was reading recently that helium supplies are getting scarce,especially with plans for heavy lift dirigibles on the drawing board.A better idea would be to collect and sell the helium as a separate revenue stream.
Eric_B
5 / 5 (1) Nov 13, 2010
That is an aluminum can, isn't it?

Ah, no wonder we haven't heard anything from the z-machine for years... I always was a fan of the beast.

Good luck!
trekgeek1
5 / 5 (2) Nov 14, 2010
There are two news breaks I'm waiting for in life.

1.) Fusion power achieved.

2.) First contact made with extraterrestrials.
Neurons_At_Work
1 / 5 (1) Nov 16, 2010
^^^
Or, extraterrestrials land, provide key to sustainable nuclear fusion. Pons and Fleischman vindicated at last!
Skeptic_Heretic
5 / 5 (2) Nov 16, 2010
Pons and Fleischman vindicated at last!
Nothing will vindicate these two of the charge of data forging.
ArcainOne
not rated yet Nov 16, 2010
There are two news breaks I'm waiting for in life.

1.) Fusion power achieved.

2.) First contact made with extraterrestrials.


I'm with you on that, whole reason I started reading at Physorg was Fusion. Granted my mother also has been waiting since the 60s for fusion, when they said the'd have it in 10 years... 10 years later they said another 10 years. Now they say first commercial in 50 or so

Though I'd have to exchange number 2 on your list with decent and probable space travel... though I guess first contact can achieve that same goal...
ekim
not rated yet Nov 16, 2010
A better idea would be to collect and sell the helium as a separate revenue stream.

Sorry to burst your bubble ,but considering the amount of hydrogen consumed compared to the energy released ,I don't think this would be a good source of helium. You would need to power the entire country this way to produce industrial quantities of helium.
Skeptic_Heretic
not rated yet Nov 17, 2010
Sorry to burst your bubble ,but considering the amount of hydrogen consumed compared to the energy released ,I don't think this would be a good source of helium. You would need to power the entire country this way to produce industrial quantities of helium.
And once we crack the underlying science of sustainable fusion power, what makes you think we wouldn't power the country and eventually the entire planet with it?
Pyle
not rated yet Nov 17, 2010
Phew. I was worried we wouldn't be able to afford floatie balloons anymore. Thank goodness fusion power is soooo close.

Oh wait, you mean we could just stop subsidizing helium production and let the artificially low price be set by the market and not run out of helium? But what about the balloons?

My money is still on lasers. Sorry z-pinch.
Newbeak
not rated yet Nov 17, 2010
Sorry to burst your bubble ,but considering the amount of hydrogen consumed compared to the energy released ,I don't think this would be a good source of helium. You would need to power the entire country this way to produce industrial quantities of helium.
And once we crack the underlying science of sustainable fusion power, what makes you think we wouldn't power the country and eventually the entire planet with it?

Yes,I never meant fusion was primarily for helium production-however,it would be a shame to just vent the helium byproduct.