Physicists demonstrate conditions for laser-driven fusion

Mar 15, 2011 by Lisa Zyga report
A mock-up of the gold-plated hohlraum used in inertial confinement fusion experiments at the National Ignition Facility. Image credit: NIF.

(PhysOrg.com) -- Currently, commercial nuclear power plants generate electricity using nuclear fission, in which an atom’s nucleus is split into lighter nuclei. But scientists are also researching the reverse reaction, nuclear fusion, in which two light atomic nuclei fuse to form a single heavier nucleus. Compared with fission, fusion has the potential to produce less radioactive waste while still generating large amounts of energy.

So far, scientists have not yet been able to produce nuclear on a large commercial scale. But two new studies published in Physical Review Letters by scientists at the National Ignition Facility (NIF), which officially opened last year at the Lawrence Livermore National Laboratory in Livermore, California, have produced some promising results.

The scientists are developing inertial confinement fusion (ICF), a type of fusion in which high-energy lasers heat and compress an inch-long gold fuel pellet called a “hohlraum” that contains the hydrogen isotope nuclei to be fused. The goal of ICF reactions is to achieve ignition, where the fusion reactions generate enough heat to be self-sustaining. The scientists hope that the fusion reactions inside the fuel pellets will generate 10-20 times more energy than that provided by the lasers that start the reactions.

In their recent experiments, the scientists at the NIF have achieved two of the most important components of ignition: extremely high “Sun-like” temperatures and uniform compression so that the targets don’t lose their shape. In the current experiments, the scientists used two-millimeter-diameter plastic spheres as the targets instead of hohlraums because they were easier to analyze.

The experiment involved focusing 192 laser beams onto the plastic spheres, each of which contained helium. The lasers generated large amounts of heat energy that was converted to X-rays with nearly 90% efficiency, and produced temperatures of up to 3.6 million degrees Celsius (300 eV). At these temperatures, the diameters of the two-millimeter spheres shrunk to about one-tenth of a millimeter.

While these conditions look promising, true ignition will involve some different components. Instead of helium, the fuel pellets will contain the element beryllium, which itself will contain the hydrogen isotopes deuterium and tritium. The laser-generated X-rays will cause the beryllium to explode, producing a reactive inward implosion that sends shockwaves into the hydrogen isotopes. The shockwaves further increase the temperature of the deuterium and tritium nuclei to the point where they can overcome their mutual repulsion and fuse.

The current experiments have simulated the conditions for such a reaction to occur in a more realistic way that any previous experiment. However, the researchers plan to take small steps toward the final goal of ignition. They’re currently testing spheres that contain unequal quantities of deuterium and tritium in order to investigate the possibility of asymmetric implosions.

Edward Moses, Associate Director of the NIF, hopes that the facility will demonstrate actual ignition in the spring or summer of 2012. However, he cautions that technical and scientific setbacks could interfere with the timeline. For instance, last January, Moses and others at the NIF had hoped to demonstrate by the end of 2010.

Explore further: Thermoelectric power plants could offer economically competitive renewable energy

More information: J. L. Kline, et al. "Observation of High Soft X-Ray Drive in Large-Scale Hohlraums at the National Ignition Facility." Physical Review Letters 106, 085003.

S. H. Glenzer, et al. "Demonstration of Ignition Radiation Temperatures in Indirect-Drive Inertial Confinement Fusion Hohlraums." Physical Review Letters 106, 085004.

via: Physics World

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User comments : 26

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Sanescience
1.7 / 5 (11) Mar 15, 2011
Meh, interesting for study but way impractical for making usable energy.
El_Nose
5 / 5 (6) Mar 15, 2011
really - why is this impractical -- i would love to hear your opinion on the matter because , well all you did was read a science arctile and say --

"man, thats the stupid way to do it. I know of a better way but I am going to keep my mouth shut until one of the Ph.d's that have written papers and studied their whole lives , decide to come and ask me how I would do it."

So, my friend -- why is this impractical???

-------------------------

I am glad the effort to increase science in this field is continuing to improve. - But it is counter intuitive that heating something to 3M Celcius would made the volume shrink -- there must be a heck of a lot of pressure being exerted on the target in the process of heating it.
TheGhostofOtto1923
3.7 / 5 (19) Mar 15, 2011
Meh, interesting for study but way impractical for making usable energy
How do you figure? Once a laser fusion 'engine' is started it will produce far more energy than it takes to run it. And lasers continue to improve on size and efficiency. This might be the best possible configuration for spacecraft propulsion.
MenaceSan
5 / 5 (7) Mar 15, 2011
TheGhostofOtto1923 there is no talk of containment or continuous fusion operation here. If i understand it correctly the laser ignition fusion would be just a repeating of the pulsed ignition as often as possible. Each fuel target would need its own laser shot in order to fuse. Of course with a 20 fold return of energy on each shot it might become profitable.
Skeptic_Heretic
4.4 / 5 (5) Mar 15, 2011
TheGhostofOtto1923 there is no talk of containment or continuous fusion operation here. If i understand it correctly the laser ignition fusion would be just a repeating of the pulsed ignition as often as possible. Each fuel target would need its own laser shot in order to fuse. Of course with a 20 fold return of energy on each shot it might become profitable.
Or with a reliable storage medium.....

Let's say one shot produces enough juice to run a mid sized city for a day. Fire off about 5 a day and you've produced enough energy to store and locally transmit for a week, no fear of fallout, no fear of pollutants, no fear of anything short of storage of said energy.

Once you determine a reasonable capture and storage medium you've won a pretty big piece of the game.
El_Nose
3 / 5 (4) Mar 15, 2011
NIF is part of the larger ITER experiment... The US was tasked with ignition - or starting the reaction, other countries got other topics according to difficulty, money allocation, or already established infrastructure that would allow them to tackle these goals.

While i cannot speak fully on whether the ignition of this reaction is long lived or not, the wording of every article i have read on the subject tends to lean on the side of we are starting a reaction that will continue until the fuel is spent.. and then we start another reaction with another piece of fuel.

The goal of ICF reactions is to achieve ignition, where the fusion reactions generate enough heat to be self-sustaining.


I believe, and i could be wrong, but I think the goal of NIF is to create an initial reaction that produces enough heat that the process coninues..

It is up to another country to tackle creating a fuel that 'lasts' a really long time.

i will look for a coutry listing of goals
sender
not rated yet Mar 15, 2011
Unfortunate that traditional magnetic field confinement is not also coupled to the reaction chamber allowing researchers to prolong the fusion reaction.
killerbunny
5 / 5 (7) Mar 15, 2011
El Nose & sender:

The ICF process is substantially different from tokamak fusion experiments, and the NIF goal (one of several...) is to research a design and implementation for a stand-alone fusion power generator. It's unrelated to the ITER project.

The reaction is not intended to be long-lived-- detonation and complete burn of all the fuel occurs on a scale of nanoseconds, after which the capsule is spent, and you need to load a new capsule in.

No matter how successful the experiments at the NIF are, that particular equipment will never be a power station because the replacement of fuel pellets requires many hours. In order for that to happen, an automated fuel pellet reloading system will have to be made, to allow for detonation to occur once every few seconds (as well as the added ability for the lasers and optics to survive such repeated use, which they current cannot).
dick_loves_otto
4 / 5 (15) Mar 15, 2011
TheGhostofOtto1923 there is no talk of containment or continuous fusion operation here. If i understand it correctly the laser ignition fusion would be just a repeating of the pulsed ignition as often as possible. Each fuel target would need its own laser shot in order to fuse. Of course with a 20 fold return of energy on each shot it might become profitable.
Its beauty is in its simplicity. No magnets sit between the reaction and the capture material, or to degrade from neutron flux. Magnets are complex and heavy systems.
Unfortunate that traditional magnetic field confinement is not also coupled to the reaction chamber allowing researchers to prolong the fusion reaction.
It is self-sustaining in that part of the captured energy is recycled into the next laser pulse. Magnetic confinement must do the same to maintain magnetic fields.
TheGhostofOtto1923
3.6 / 5 (17) Mar 15, 2011
Sorry about the idiot sockpuppet - otto has been interacting with a little chigger troll named dick_wolf. But who is he really? Cmon dick - expose yourself.

I see laser fusion as either the core of a beam weapon or, like I said, as a form of propulsion. Something like this:
http
://en.wikipedia.org/wiki/Project_Daedalus
TheGhostofOtto1923
3.6 / 5 (17) Mar 15, 2011
Heres an even better one I wasnt aware of:
http
://en.wikipedia.org/wiki/Project_Longshot
Skeptic_Heretic
3.5 / 5 (4) Mar 15, 2011
Cmon dick - expose yourself.

Typically I unzip when I want my dick to expose itself.
Jaeherys
1 / 5 (1) Mar 15, 2011
What about inertial electrostatic confinement fusion? I watched a lecture about it a while ago and it sounded promising. Is there something about it that has made it not recieve further funding?

@Skeptic_Heretic
Would a kinetic storage device be applicable? IE, some massive rotating object storing energy and releasing it by running generators when needed? I know there would be loss of energy due to the efficiency of the generators but would it be even remotely possible?
unknownorgin
1.3 / 5 (3) Mar 16, 2011
What is needed is a way to cause fusion without investing huge amounts of energy back into the reaction, A star uses gravity to generate the pressure needed. Some say a fusion reactor that will generate just enough power to run itself would be about a cubic mile in size using current technology.
The whole laser/ feul pellet idea has been tried for at least a decade and the money spent on fusion research could have put working technology in place to cut back foriegn oil dependance.

Eikka
not rated yet Mar 16, 2011
Somehow this reminds me of the idea of a combustion engine that runs on guncotton string. The basis of operation being that a blade cuts a piece of the explosive string and then the piston slams it against the cylinder head. They actually did build one, and it did blow up to pieces like you would have guessed.

What they have there is literally a tiny hydrogen bomb being detonated every second or twice a second, however many you need to produce some average power. I would like to see the structure that can withstand a million of those. With the kind of repeated stress to create, say 1 GW power on average from a series of nuclear explosions, any structure that I can think of would turn to dust.
Eikka
not rated yet Mar 16, 2011
Because even in combustion engines, that people like to think of as running on explosions, the actual process is much gentler. It's combustion like the name says - the chemical chain reaction never goes faster than the speed of sound, which makes the pressure build-up smooth.

But if you increase the pressure enough, or use an unsuitable fuel, the mixture in the cylinder doesn't follow a chain reaction anymore. It lights up spontaneously everywhere and that makes the pressure build-up faster than the speed of sound - a shockwave - an explosion that puts immense stress on the parts until the cylinder or the cylinder head, or the piston, or anything subjected to the battering just gives up and fractures after a number of repeated explosions.

Running on explosions instead of combustion would make the engine incredibly efficient, but there's simply no material that can withstand it for a long time. That's why the guncotton engine failed as well.

And now they're trying it with h-bombs.
rbrtwjohnson
not rated yet Mar 16, 2011
The laser-driven fusion scheme is technically an unpractical way of producing electric energy from fusion reactions. I think electrostatic fusion reactors, such as Farnsworth-Hirsch Fusor, Bussard Polywell, and CrossFire Fusion Reactor, are conceptually smarter designs that if correctly funded can produce more practical results with less money than these behemoths NIF and ITER.
Skeptic_Heretic
5 / 5 (2) Mar 16, 2011
@Skeptic_Heretic
Would a kinetic storage device be applicable? IE, some massive rotating object storing energy and releasing it by running generators when needed? I know there would be loss of energy due to the efficiency of the generators but would it be even remotely possible?
I really can't speak to that. It's outside my expertise.
Tangent2
1 / 5 (1) Mar 20, 2011
Running on explosions instead of combustion would make the engine incredibly efficient, but there's simply no material that can withstand it for a long time. That's why the guncotton engine failed as well.

And now they're trying it with h-bombs


They are getting pretty close to this though, an engine without as many moving parts and works with shockwaves:
http://www.physor...deo.html
stealthc
1 / 5 (1) Mar 20, 2011
why use gold? Why not use lead so the by-product of the reaction is gold then you can sell the fusion waste for some good money.
GSwift7
3.7 / 5 (3) Mar 21, 2011
@Skeptic_Heretic
Would a kinetic storage device be applicable? IE, some massive rotating object storing energy and releasing it by running generators when needed? I know there would be loss of energy due to the efficiency of the generators but would it be even remotely possible?
I really can't speak to that. It's outside my expertise.


Just like a fission reactor, the energy will be thermal. You collect and store the energy with heat sinks and a liquid salt. Then you use the heated salt to boil water at a controlled rate and drive standard steam turbines. The setup should be quite similar to existing nuclear power plants. If the heat comes in pulses then you just use pressure dampers. The reverse of an aircraft carrier steam catapult or the damping system on a 20 inch gun for example. That way the pressure/temperature of the pulse is mechanically conserved in the system. You could do it with just a few moving parts, just like a standard nuclear plant.
Jaeherys
3 / 5 (2) Mar 22, 2011
Sometimes I guess it's best to stick with what works. Are there more efficient ways to convert the thermal energy into electricity?
GSwift7
4 / 5 (4) Mar 24, 2011
to Jaeherys:

The method of using a heated liquid salt to store the energy is super-efficient except that the salts tend to be really corrosive, especially at high temperatures, so it's a little rough on maintenance of valves, seals and such. The newest generation of steam turbines and live steam handling methods have come from nearly 100 years of experience and it is an extremely mature technology. The infrastructure to supply replacement parts and to supply educated people to run them is very established. That greatly lowers the final cost to operate. If you could find a technology that is a little more efficient then you still have to face the barriers of getting a new technology established well enough that the final costs (including all the logistical and technical support costs) do not cost more than what you gain from effiency. Lots of people don't understand that the "best" technology on paper isn't always the same as the most economical in the real world.
GSwift7
4 / 5 (4) Mar 24, 2011
Looking at three examples:

Digital cameras have completely replaced film cameras and now excede film in performance and cost by far. It has become mature.

Flat panel display is still in flux. The cost is still a bit high, and standards have not become firm yet (eg: plasma vs LED).

Compact flourescent lightbulbs are still in the early stages of the cycle and may never make it to the end. They cost too much and LED lighting seems to be on the path to preempt them.

Any new energy tech (solar, tidal, fusion) must get over this learning curve/product developement cycle. The more radical a tech, the steeper the curve. That partially explains why you sometimes see a way people could improve something (a car for example) but for some seemingly inexplicable reason, the lunkheads in charge won't do it. In the big picture, they aren't really lunkheads. They do the math and figure out the total cost to market and sometimes it just doesn't add up for them. It's about making a profit.
GSwift7
3.7 / 5 (3) Mar 24, 2011
The CFL example neatly illustrates another fine point that escapes many casual observers. Investment in a new industry is substantial. If it is replaced by a better alternative before you can make enough money to cover the costs, then you are screwed. So, if you wanted to start making solar panels, for example, you would want to make sure that you'd be able to sell enough of your type of solar panels to make a profit before someone else comes up with an improved design that doesn't fit your manufacturing methods. There's always a risk. That's where government/university/business partnerships come in. Like right now we see concentrated solar thermal pilot plants being constructed in a few places. They are largely funded by research grants because investors can see that the cost is really high and the time it takes to pay back the investments is really long. That increases the risk that it will be replaced by something better before it can mature. ARPAe and DARPA focus on that problem.
Jaeherys
2.7 / 5 (3) Mar 24, 2011
I am by no means a business man but that does make sense. I am a chem student and programmer by hobby and even with programming languages or libraries, maturity really does make a big difference; look at the c++ STD or boost.

I guess as someone who can see all these amazing new discoveries coming about and with a lack of "real life" experience (as I am still a student) you tend to forget about all that other stuff, mainly everything to do with production lol.

That's one of the reasons I have gone into chemistry as relatively small changes in production, IE., small chemical changes, can make a great difference. That and I want to go into space by elevator, but one has to have dreams!

Thanks for the informative replies!

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