Laser-heated nanowires produce micro-scale nuclear fusion with record efficiency

March 14, 2018 by Anne Manning, Colorado State University
The target chamber (front) and ultra-high intensity laser (back) used in the micro-scale fusion experiment at Colorado State University. Credit: Advanced Beam Laboratory/Colorado State University

Nuclear fusion, the process that powers our sun, happens when nuclear reactions between light elements produce heavier ones. It's also happening—at a smaller scale—in a Colorado State University laboratory.

Using a compact but powerful to heat arrays of ordered nanowires, CSU scientists and collaborators have demonstrated micro-scale nuclear in the lab. They have achieved record-setting efficiency for the generation of neutrons—chargeless sub-atomic particles resulting from the fusion process. Their work is detailed in a paper published in Nature Communications, and is led by Jorge Rocca, University Distinguished Professor in electrical and computer engineering and physics. The paper's first author is Alden Curtis, a CSU graduate student.

Laser-driven controlled fusion experiments are typically done at multi-hundred-million-dollar lasers housed in stadium-sized buildings. Such experiments are usually geared toward harnessing fusion for clean energy applications.

In contrast, Rocca's team of students, research scientists and collaborators, work with an ultra fast, high-powered tabletop laser they built from scratch. They use their fast, pulsed laser to irradiate a target of invisible wires and instantly create extremely hot, dense plasmas—with conditions approaching those inside the sun. These plasmas drive fusion reactions, giving off helium and flashes of energetic neutrons.

Top left: A scanning electron microscope image of aligned deuterated polyethylene nanowires. The other panels are 3-D simulations of the nanowires rapidly exploding following irradiation by an ultra-intense laser pulse. Credit: Advanced Beam Laboratory/Colorado State University

In their Nature Communications experiment, the team produced a record number of neutrons per unit of laser energy—about 500 times better than experiments that use conventional flat targets from the same material. Their laser's target was an array of nanowires made out of a material called deuterated polyethylene. The material is similar to the widely used polyethylene plastic, but its common hydrogen atoms are substituted by deuterium, a heavier kind of hydrogen atom.

The efforts were supported by intensive computer simulations conducted at the University of Dusseldorf (Germany), and at CSU.

Making fusion neutrons efficiently, at a small scale, could lead to advances in -based imaging, and neutron probes to gain insight on the structure and properties of materials. The results also contribute to understanding interactions of ultra-intense laser light with matter.

Explore further: Shedding high-power laser light on the plasma density limit

More information: Alden Curtis et al, Micro-scale fusion in dense relativistic nanowire array plasmas, Nature Communications (2018). DOI: 10.1038/s41467-018-03445-z

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24volts
2.5 / 5 (4) Mar 14, 2018
Sounds a lot like the beginning steps to a portable fusion power supply to me but that's just my opinion.
Wouldn't it be interesting though if some scientist and engineers come up with one that is efficient and cheap to operate before any big fusion systems come on-line?
That's assuming they eventually get it to work and actually produce excess power that can be harnessed for other uses.
Who knows, maybe 50-100 years from now everyone will have a small fusion system that powers their homes or maybe the block instead of having to hook up to a mains system.
eachus
2.3 / 5 (3) Mar 14, 2018
The number of neutrons generated is far short of fusion breakeven. Using a 50/50 mix of tritium and deuterium should help a lot. More interesting would be to use lithium deuteride to manufacture the wires. A lot of the energy must be going into the (relatively high Z) carbon atoms, with no benefit to the reaction. Lithium, of course, has Z of three, and more important lithium can react with the neutrons, protons and deuterons flying around and give off much more energy.

Technically this is building a table-top thermonuclear device, but assuming the math is done right, the explosion would be small enough to be contained. In case this idea worries you? Don't panic. Managing to break a flask or two would be wonderful news. It would probably require years of research to get explosions on the scale of those in your car engine. The GE pavilion at the New York World's Fair over 50 years ago had a Z-pinch that was on this scale.
TheGhostofOtto1923
3 / 5 (5) Mar 15, 2018
Sounds a lot like the beginning steps to a portable fusion power supply to me
To me it sounds a lot like you're unaware that it takes a lot more energy to create these reactions, than is actually created by these reactions. Same with muon-catalyzed fusion.
Technically this is building a table-top thermonuclear device, but assuming the math is done right, the explosion would be small enough to be contained
No, because as you stated in your first paragraph the apparatus would have to generate more energy than is produced by the reaction. Somewhat like using a nuclear weapon to trigger a chemical explosion.
TheGhostofOtto1923
2.5 / 5 (4) Mar 15, 2018
It's the same with commercially-available neutron generators.

"When deuterium is used in the ion beam, two deuterium ions fuse (D-D fusion), while if tritium is used, a deuterium and a tritium ion fuse (D-T fusion). In both cases, neutrons are by products of the fusion reaction."

"Thousands of such small, relatively inexpensive systems have been built over the past five decades."
antialias_physorg
3.8 / 5 (5) Mar 15, 2018
Sounds a lot like the beginning steps to a portable fusion power supply to me but that's just my opinion.

Not really, as you're destroying the target in the process and the neutron output is also very low compared to the energy of the laser (2 million neutrons per joule of laser energy).

For comparison: The test shots at the NIF produce around 4 billion neutrons per joule. (i.e the stuff in the article above is far from break-even...let alone giving a net energy return)

The big advantage, though, is that with a low power laser you can shoot a lot more often than with the high power lasers at the NIF which makes it suitable for the stated applications of a good, consistent, pinpoint neutron source for neutron imaging/neutron tomography.
gculpex
2 / 5 (4) Mar 15, 2018
Clickbait..... add the word 'Fusion' and they will come.
24volts
3 / 5 (2) Mar 15, 2018
I said a BEGINNING people.. that's a long long way from producing anything useable!

You have to start somewhere and the scientists building the big stuff have been doing it for about 50 years and still haven't built anything that actually works to provide any useful power either.

THEY are also still at the beginning but they have wasted a hell of a lot of other people's money getting basically nowhere so far except that they have learned a lot of what doesn't work.
antialias_physorg
4 / 5 (4) Mar 15, 2018
Fusion doesn't magically create energy. You need to catch the neutrons, convert them to heat, convert that to steam and run a turbine (or use thermoelectric converter which have atrociously low efficiencies)

There's also the radiation to think about. Neutron radiation isn't particularly healthy (and - due to the electrically neutral charge only really shielded by putting some serious material in the way.
Shielding works with inelastic scattering or neutron capture (which in turn makes your shielding radioactive over time). Both require very heavy elements (or several meters of concrete - which is the 'biological shield' dome that you see surrounding nuclear reactors)

I'm pretty sure we're not going to see a portable "Mr. Fusion" in the future. That's not a matter of better engineering. There's some serious physics that says so..
24volts
3 / 5 (2) Mar 15, 2018
AP, I know what it takes to convert heat into power. I wasn't commenting on that. Don't you be so sure what 50-100 years might or might not bring.
You can place a winning bet that 100 years people would have never thought that you could set a 400 hp gasoline engine on the average school desk either. An engine that powerful was the size of a warehouse back then.
Or that you would be carrying around in a pocket a computer system that is 1000+ times more capable than when they first came out and took up an entire building. You just never know.....
antialias_physorg
3.7 / 5 (6) Mar 16, 2018
Don't you be so sure what 50-100 years might or might not bring.

In engineering there's always room for cool break throughs. But we're not talking engineering, we're talking physics. Particularly exponential laws when it comes to shielding and biology in the form of susceptibility of biological matter - humans - to neutron radiation. Neither of those is open to being changed by engineering.

You're essentially arguing on the lines of: "with better engineering we'll have a perpetuum mobile" - and I'm saying: "ain't gonna happen because: physics"

You can place a winning bet that 100 years people would have never thought that you could set a 400 hp gasoline engine on the average school desk either.

However, building such a thing does not clash with the laws of physics anywhere.

In the words of our most beloved TV-Character: "Captain, I cannot change the laws of physics!"
TheGhostofOtto1923
2.3 / 5 (3) Mar 16, 2018
This is both good new both bad new, because neutrons would make whole reactor radioactive
Commercial neutron generators don't make themselves radioactive
https://www.therm...nerators
Urgelt
not rated yet Mar 19, 2018
Auntie wrote, "...I'm saying: "ain't gonna happen because: physics..."

I'm uncomfortable with Auntie's position on this.

Physics says fusion works just fine. Ignition isn't a problem, either. The difficulties are how to confine plasma long enough to get useful fusion events out of it, how to draw off heat energy without wrecking the reactor and how to make it all work continuously, or at least with sufficiently-rapid pulses to turn the thing into a useful power source.

Physics says this is going to be hard. Fusion generates hot temperatures that are destructive to any materials we could create. But physics doesn't say there is no solution. Plasma can be confined electromagnetically, inertially or in combination. An awfully large number of physicists and engineers are actively working on the problem; if those guys and gals thought physics makes fusion power generation impossible, I suspect they'd find something else to do with their degrees and their effort.
antialias_physorg
5 / 5 (1) Mar 19, 2018
Physics says fusion works just fine. Ignition isn't a problem, either.

I'm not saying that fusion doesn't work that way. I'm saying that fusion (and fission) creates neutron radiation and neutron radiation isn't anything you want to be near to because it's very bad for humans.

It isn't amenable to be easily shielded from (since neutrons are electrically neutral you can't just throw electric or magnetic fields at the problem). There's no magic 'trick' that will make neutron radiation stop except a LOT of material (or a little less very dense material) in the way. Notice the several meters thick walls of concrete around nuclear powerplants (or how the LHC is WAY underground)? That's why.

It's no coincidence that someone came up with a neutron bomb because they kill everything inside buildings but leave the buildings themselves standing. Neutron radiation is just nasty that way.
eachus
not rated yet Mar 19, 2018
Fusion doesn't magically create energy. You need to catch the neutrons, convert them to heat, convert that to steam and run a turbine (or use thermoelectric converter which have atrociously low efficiencies)


Running at high temperatures, or capturing the energy from charged particles can get you over 50%,

There's also the radiation to think about. Neutron radiation isn't particularly healthy (and - due to the electrically neutral charge only really shielded by putting some serious material in the way.
Shielding works with inelastic scattering or neutron capture (which in turn makes your shielding radioactive over time). Both require very heavy elements (or several meters of concrete - which is the 'biological shield' dome that you see surrounding nuclear reactors)


The best neutron shielding is hydrogen, and it is the water bound in the concrete that makes it useful for stopping neutrons.

H1 + Be11 is aneutronic, but needs higher energies.
Urgelt
not rated yet Mar 19, 2018
Okay, Auntie, I see where you are coming from.

But neutron production isn't just waste from fusion reactions. The trick is getting them to do what we want them to do - which isn't easy, as you pointed out, since they are electrically neutral.

On average, across the space each neutron occupies, they're electrically neutral.

But dig deeper, and you'll find that they are *not* electrically neutral; they have charges, and those charges manifest differently in different parts of the particle. They *sum* to zero, but those charges don't go away. So while it's true that a simple electromagnet can't provide confinement, it's not true that an electromagnet can't affect a neutron.

From a theoretical standpoint, physics isn't saying that any reaction that produces neutrons is useless. Neutrons are a potentially useful product. We just have to figure out how to get them to do what we want them to do. Crudely, we're already doing that with neutron imaging.
antialias_physorg
not rated yet Mar 19, 2018
The best neutron shielding is hydrogen, and it is the water bound in the concrete that makes it useful for stopping neutrons.

24volts was phantasizing about portable fusion devices. Several meters of shielding does not make for 'portable' anything.

The trick is getting them to do what we want them to do - which isn't easy, as you pointed out, since they are electrically neutral.

That's where physics comes into play as opposed to engineering. There's no trick you can pull with neutrons.
They *sum* to zero, but those charges don't go away.

You can affect the spin of a neutron with an external field (e.g. you can polarize a neutron beam). You cannot affect the path. The path is where it's at when you try to shield neutron radiation.
24volts
not rated yet Mar 19, 2018
No, I didn't "phantasize' about anything. I said one day there might be home sized or block sized versions. Not only do you have problems with basic reading comprehension of simple sentences but you can't spell either.
Da Schneib
not rated yet Mar 19, 2018
I don't think this is a path to net-power fusion. I think the provision of fuel is the primary barrier to that here.

In general, I have noted over a long period of time that a star seems like the most efficient fusion engine possible. You fuel it once and it burns for billions of years. Capturing energy from it seems to work fine for terrestrial worlds, given our experience. Using technology we are in the process of developing seems the most efficient way to get more energy out of it. It is gravitically confined by its own mass requiring no complicated confinement. Stay far enough away from it and you have no contamination or radiation problems.

Seems like we'll need gravitic confinement to really make a success of fusion to me, though there are a couple of electric confinement schemes we're working on that might work. As @anti points out, however, we'll need to fix the neutron problem.
Urgelt
not rated yet Mar 20, 2018
Auntie wrote, "Several meters of shielding does not make for 'portable' anything."

Tell that to Lockheed. They're still puttering away on a tractor-trailer-sized 100 MW fusion power reactor, and they intend to sell the things on movable trailers, if they can get them to work.

Will they? Beats me. I suppose the predominant view is they'll fail. But it's not that physics demands failure; it's that it's a damned difficult engineering problem, and there are still things to learn about plasma physics, which means a lot of trial-and-error engineering.

A tractor-trailer sized 100 MW fusion power generator would be launchable; we could use it as the power source for interplanetary vessels. I won't count that chicken until it hatches, but it sure would make it easier to expand our economy into space.

antialias_physorg
3 / 5 (2) Mar 20, 2018
said one day there might be home sized or block sized versions.

Then I must have misread the first sentence you posted in this thread:
"Sounds a lot like the beginning steps to a portable fusion power supply to me"

We may have differing opinions what constitutes 'portable'. If you say there may be stuff that needs not be fixed in place then I agree. We'll eventually have that (not least of which on spacecraft). But we'll certainly not be carrying these suckers around.

Not only do you have problems with basic reading comprehension of simple sentences but you can't spell either.

Ya know: when you speak/write german as well as I do english you can give me advice. Before that - meh.

antialias_physorg
not rated yet Mar 20, 2018
Tell that to Lockheed. They're still puttering away on a tractor-trailer-sized 100 MW fusion power reactor, and they intend to sell the things on movable trailers, if they can get them to work.

From the wiki link:
The "blanket" component that lines the reactor vessel has two functions: it captures the neutrons and transfers their energy to a coolant and forces the neutrons to collide with lithium atoms, transforming them into tritium to fuel the reactor. The blanket would be an estimated 80–150 cm thick and weigh 300–1000 tons

See? They do need massive shielding. No magic trick there, either.

From an engineering standpoint I find it much more likely that we'll get to the point where decreasing energy needs due to higher efficiency in our gadgets/heating/lighting meets increasing ambient energy harvesting capabilities. Zero (or net negative) energy homes are already a reality. Less spectacular, but a lot more realistic (and safe).
Urgelt
not rated yet Mar 20, 2018
Oh, Lockheed's approach does require shielding, yep, yep. It's not going to fit into a suitcase, that's for certain. Might could be their design objective of fitting it onto a semi-trailer won't work, either. And it might end up not being launchable - assuming they can get something working at all.

Wikipedia doesn't actually have much of a window into what Lockheed is skunking up. But I agree, there's no magic trick to make the neutron problem go away.

I also agree that your scenario about meeting our needs with less spectacular methods is probably more likely, but that won't give us a fusion drive for interplanetary uses. So I reserve in my head a place to hope that projects like Lockheed's might one day deliver something useful for that purpose.
antialias_physorg
3 / 5 (2) Mar 20, 2018
Sure. I also hope that Lockheed succeeds - and, of course, ITER, too. I'm sure there are some power hungry industries that would love to have such a power source (though knowing Lockheed Martin it's a lot more likely this stuff ends up on warships and similar insane contraptions)
Urgelt
not rated yet Mar 20, 2018
Well, sure. Of course they'll use it to power weapons.

But if they can use it for that, it *should* be launchable.

I take my silver linings where I can find them.
eachus
1 / 5 (1) Mar 20, 2018
Decades ago I designed two different fusion power sources. Not all the engineering was done, but I could make a first cut at economics showed that they would never happen. The first used a wall-stabilized arc with a z-pinch down the center. The family business was then building pulsed xenon lamps, mostly for photo-lithography, so most of the math was familiar. Substitute deuterium-tritium for the xenon and use magnetic fields to keep the high temperature from eating the electrodes at either end. (Some plasma would leak through, just keep it from melting the electrodes.) The problem? Keeping the wall solid in the middle--it would be a few millimeters from from the hottest part of the plasma--limits the power that could be generated. And even putting hundreds of them in one spot to share shielding, the cost would be way to high.
eachus
1 / 5 (1) Mar 20, 2018
The other idea was a magnetic mirror machine a few miles long. There was enough experimental data on end cap leakage to show it would work, but all the engineering details like breeding blankets, and converting heat in that blanket into electricity would require ITER-scale testing. The big problem would be the heat-exchangers. There have been lots of development issues with cooling molten sodium from fast breeder reactors. I would favor using a Lithium Fluoride molten salt blanket. But again. I couldn't imagine any company would be willing to bet on a power plant that could power say the Eastern Seaboard from Boston through Washington. The price of energy fluctuates too much on a multi-decade scale to convince anyone to sign up. At that time the idea of building solar power satellites in L5 from lunar materials looked like a much better bet. And in fact the Falcon Heavy has just dropped the price of doing that.. :-)

So don't forget the economics!
DonGateley
not rated yet Mar 24, 2018
Oh, Lockheed's approach does require shielding, yep, yep. It's not going to fit into a suitcase, that's for certain. Might could be their design objective of fitting it onto a semi-trailer won't work, either. And it might end up not being launchable - assuming they can get something working at all.


They probably plan to call up Elon, Bore a corkscrew into a mountain as far as necessary, drive the damn thing in and fire it up. Then they'll put one on one of his BFR's and orbit it. I don't know if the latter is actually feasible but either is just the kind of challenge Elon seems to love.
Mark Thomas
not rated yet Apr 26, 2018
We'll eventually have that (not least of which on spacecraft).


People have speculated that a high-performance fusion reactor, maybe third generation or later, would allow us to build spacecraft that travel a a decent fraction of the speed of light. This would open up the entire solar system to crewed exploration. Imagine trips to Mars as short at two weeks and boots on Eris. I would LOVE to see that put to the test, but I am not counting on ITER because for each year that passes, the planned start of D-T fusion is also delayed a year or so. Currently ITER is planning D-T fusion to begin in 2035. This is extremely disappointing and probably needs to be investigated, again.

https://www.iter....e/-/2588

Take a look at the participants' faces in the picture by following my link. It is good bet that most or all of them will be retired by 2035. Must be nice to agree to a deadline after your retirement date.

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