Physicists see solution to critical barrier to fusion

Apr 23, 2012 By John Greenwald
An in-depth analysis by Luis Delgado-Aparicio (left) and David Gates (right), scientists from the U.S Department of Energy's Princeton Plasma Physics Laboratory zeroed in on tiny, bubble-like islands that appear in hot, charged gases -- or plasmas -- during experiments. They believe they may have found a solution to a critical barrier to fusion. Credit: Elle Starkman/Princeton Plasma Physics Laboratory Office of Communications

(Phys.org) -- Physicists have discovered a possible solution to a mystery that has long baffled researchers working to harness fusion. If confirmed by experiment, the finding could help scientists eliminate a major impediment to the development of fusion as a clean and abundant source of energy for producing electric power.

An in-depth analysis by scientists from the U.S. Department of Energy's Princeton Physics Laboratory (PPPL) zeroed in on tiny, bubble-like islands that appear in the hot, charged —or plasmas—during experiments. These minute islands collect impurities that cool the plasma. And it is these islands, the scientists report in the April 20 issue of , that are at the root of a long-standing problem known as the "density limit" that can prevent fusion reactors from operating at maximum efficiency.

Fusion occurs when plasmas become hot and dense enough for the atomic nuclei contained within the hot gas to combine and release energy. But when the plasmas in experimental reactors called tokamaks reach the mysterious density limit, they can spiral apart into a flash of light. "The big mystery is why adding more heating power to the plasma doesn't get you to higher density," said David A. Gates, a principal research physicist at PPPL and co-author of the proposed solution with Luis Delgado-Aparicio, a post-doctoral fellow at PPPL and a visiting scientist at MIT's Plasma Science Fusion Center. "This is critical because density is the key parameter in reaching fusion and people have been puzzling about this for 30 or 40 years."

The scientists hit upon their theory in what Gates called "a 10-minute 'Aha!' moment." Working out equations on a whiteboard in Gates' office, the focused on the islands and the impurities that drive away energy. The impurities stem from particles that the plasma kicks up from the tokamak wall. "When you hit this magical density limit, the islands grow and coalesce and the plasma ends up in a disruption," says Delgado-Aparacio.

These islands actually inflict double damage, the scientists said. Besides cooling the plasma, the islands act as shields that block out added power. The balance tips when more power escapes from the islands than researchers can pump into the plasma through a process called ohmic heating—the same process that heats a toaster when electricity passes through it. When the islands grow large enough, the electric current that helps to heat and confine the plasma collapses, allowing the plasma to fly apart.

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David Gates and Luis Delgado-Aparicio discuss a solution they discovered that could eliminate a critical barrier to fusion. Credit: John Greenwald/PPPL Office of Communications

Gates and Delgado-Aparicio now hope to test their theory with experiments on a tokamak called Alcator C-Mod at MIT, and on the DIII-D tokamak at General Atomics in San Diego. Among other things, they intend to see if injecting power directly into the islands will lead to higher density. If so, that could help future tokamaks reach the extreme density and 100-million-degree temperatures that fusion requires.

The scientists' theory represents a fresh approach to the density limit, which also is known as the "Greenwald limit" after MIT physicist Martin Greenwald, who has derived an equation that describes it. Greenwald has another potential explanation of the source of the limit. He thinks it may occur when turbulence creates fluctuations that cool the edge of the plasma and squeeze too much current into too little space in the core of the plasma, causing the current to become unstable and crash. "There is a fair amount of evidence for this," he said. However, he added, "We don't have a nice story with a beginning and end and we should always be open to new ideas."

Gates and Delgado-Aparicio pieced together their model from a variety of clues that have developed in recent decades. Gates first heard of the density limit while working as a post-doctoral fellow at the Culham Centre for Fusion Energy in Abingdon, England, in 1993. The limit had previously been named for Culham scientist Jan Hugill, who described it to Gates in detail.

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Click here for a podcast interview with physicists Luis Delgado-Aparicio and David Gates.

Separately, papers on plasma islands were beginning to surface in scientific circles. French physicist Paul-Henri Rebut described radiation-driven islands in a mid-1980s conference paper, but not in a periodical. German physicist Wolfgang Suttrop speculated a decade later that the islands were associated with the density limit. "The paper he wrote was actually the trigger for our idea, but he didn't relate the islands directly to the Greenwald limit," said Gates, who had worked with Suttrop on a tokamak experiment at the Max Planck Institute for Plasma Physics in Garching, Germany, in 1996 before joining PPPL the following year.

In early 2011, the topic of plasma islands had mostly receded from Gates' mind. But a talk by Delgado-Aparicio about the possibility of such islands erupting in the plasmas contained within the Alcator C-Mod tokamak reignited his interest. Delgado-Aparicio spoke of corkscrew-shaped phenomena called snakes that had first been been observed by PPPL scientists in the 1980s and initially reported by German physicist Arthur Weller.

Intrigued by the talk, Gates urged Delgado-Aparicio to read the papers on islands by Rebut and Suttrop. An email from Delgado-Aparicio landed in Gates' in-box some eight months later. In it was a paper that described the behavior of snakes in a way that fit nicely with the C-Mod data. "I said, 'Wow! He's made a lot of progress,'" Gates remembers. "I said, 'You should come down and talk about this.'"

What most excited Gates was an equation for the growth of islands that hinted at the density limit by modifying a formula that British physicist Paul Harding Rutherford had derived back in the 1980s. "I thought, 'If Wolfgang (Suttrop) was right about the islands, this equation should be telling us the Greenwald limit," Gates said. "So when Luis arrived I pulled him into my office."

Then a curious thing happened. "It turns out that we didn't even need the entire equation," Gates said. "It was much simpler than that." By focusing solely on the density of the electrons in a plasma and the heat radiating from the islands, the researchers devised a formula for when the heat loss would surpass the electron density. That in turn pinpointed a possible mechanism behind the Greenwald limit.

Delgado-Aparicio became so absorbed in the scientists' new ideas that he missed several turnoffs while driving back to Cambridge that night. "It's intriguing to try to explain Mother Nature," he said. "When you understand a theory you can try to find a way to beat it. By that I mean find a way to work at densities higher than the limit."

Conquering the limit could provide essential improvements for future tokamaks that will need to produce self-sustaining fusion reactions, or "burning plasmas," to generate electric power. Such machines include proposed successors to ITER, a $20 billion experimental reactor that is being built in Cadarache, France, by the European Union, the United States and five other countries.

Why hadn't researchers pieced together a similar theory of the density-limit puzzle before? The answer, says Gates, lies in how ideas percolate through the scientific community. "The radiation-driven islands idea never got a lot of press," he says. "People thought of them as curiosities. The way we disseminate information is through publications, and this idea had a weak initial push."

PPPL, in Plainsboro, N.J., is devoted both to creating new knowledge about the physics of plasmas – ultra-hot, charged gases – and to developing practical solutions for the creation of fusion energy. Through the process of , which is constantly occurring in the sun and other stars, energy is created when the nuclei of two lightweight atoms, such as those of hydrogen, combine in plasma at very high temperatures. When this happens, a burst of energy is released, which can be used to generate electricity.

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Telekinetic
3 / 5 (17) Apr 23, 2012
I wonder what those who claim that fusion won't be viable for decades would say after seeing this development. It would be amazing if it pans out. Then all of the objections to electric cars would be silenced, and we could be free of any Fukushima-type disasters in the future.
Sonhouse
1.2 / 5 (11) Apr 23, 2012
A working fusion reactor would certainly not be as bad as Fuku and such but it would not be like air compressor suddenly being dropped 6 feet. There would be radiation leaked out just not near as much.
Terriva
1.4 / 5 (44) Apr 23, 2012
Physicists see solution to critical barrier to fusion
I would rather say, the physicists do perceive the nearing competition of cold fusion nervously and they're playing for time before publics. Because the first successful application of cold fusion would wipe their useless research completely and undeniably. They had no practical results with it during last fifty years - so why we should expect the turnover right now?
Telekinetic
3.5 / 5 (24) Apr 23, 2012
A working fusion reactor would certainly not be as bad as Fuku and such but it would not be like air compressor suddenly being dropped 6 feet. There would be radiation leaked out just not near as much.

Infinitesimal in comparison without the possibility of a meltdown.
Telekinetic
2.2 / 5 (13) Apr 23, 2012
Physicists see solution to critical barrier to fusion
I would rather say, the physicists do perceive the nearing competition of cold fusion nervously and they're playing for time before publics. Because the first successful application of cold fusion would wipe their useless research completely and undeniably. They had no practical results with it during last fifty years - so why we should expect the turnover right now?

Well, if it's competition that inspires innovation, then bring it on!
Shelgeyr
3.5 / 5 (16) Apr 23, 2012
@Telekinetic said:
I wonder what those who claim that fusion won't be viable for decades would say after seeing this development.


How about "Hurray!" since at least for many of us, I assume this is one of those "I'd be happy to be wrong" issues.

@Sonhouse said:
A working fusion reactor would certainly not be as bad as Fuku... ...There would be radiation leaked out just not near as much.


My understanding from my fusion physics and power generation courses decades ago (please note: I'm admitting my education is out of date, but hey, Tokamaks haven't seemed to have made a ton of progress since then...) is that with any loss of power there would be a nigh-instantaneous loss of magnetic constriction and thus an immediate loss of fusion. Supposedly no radiation danger at all.

Our professor, who was pretty cool, took the time to point out the scientific flaws in the movie "Aliens" regarding the fate of their great big fusion reactor / air processing plant. That was fun...
axemaster
5 / 5 (18) Apr 23, 2012
I wonder what those who claim that fusion won't be viable for decades would say after seeing this development.

Fusion won't be viable for decades. Even if this pans out, and hopefully it will, it will still take 10-20 years just to finish experiments so that we understand how to actually go about designing a proper fusion reactor. And then another 10 years to start implementation. It's sad, I know, but it's also the truth.
aroc91
3.6 / 5 (8) Apr 23, 2012
Then all of the objections to electric cars would be silenced


As they exist now, the source of power for electric cars isn't the only issue with them, so I disagree. The manufacturing of the batteries themselves is still environmentally unfriendly.
Telekinetic
1.7 / 5 (20) Apr 23, 2012

"Fusion won't be viable for decades. Even if this pans out, and hopefully it will, it will still take 10-20 years just to finish experiments so that we understand how to actually go about designing a proper fusion reactor. And then another 10 years to start implementation. It's sad, I know, but it's also the truth."

The U.S. beat the Germans at building the first atomic weapon in a two or three year period at a time when nuclear know-how was in its infancy. They should easily be able to alter or adapt equipment in short order to test the new finding. It's sad, I know, but you're wrong.
Telekinetic
2.5 / 5 (19) Apr 23, 2012
Then all of the objections to electric cars would be silenced


As they exist now, the source of power for electric cars isn't the only issue with them, so I disagree. The manufacturing of the batteries themselves is still environmentally unfriendly.

Compared to the internal combustion engine and the havoc it's wreaked on this planet, I would plant lithium-air batteries next to my daffodils. Get some perspective.
sirchick
5 / 5 (15) Apr 23, 2012
Physicists see solution to critical barrier to fusion
I would rather say, the physicists do perceive the nearing competition of cold fusion nervously and they're playing for time before publics. Because the first successful application of cold fusion would wipe their useless research completely and undeniably. They had no practical results with it during last fifty years - so why we should expect the turnover right now?


The fact you said "their useless research" already proves you're not the best scientifically minded person - no research is ever "useless" its all learning - learning is never useless.

This flawed you're comment before even mentioning cold fusion.

MB2BM55
1.8 / 5 (5) Apr 23, 2012


Jeddy_Mctedder
2.8 / 5 (13) Apr 23, 2012
if fusion power ever happens, you can bet its going to come from people in princeton and general dynamics working together. that said, fusion funding is getting more and more pressure. they've been spending GOOD MONEY for a long time chasing this thing. it's almost like a cult. i know an up and coming star in the fusion community who is 30 years old and 3-4 years in at DiiiD at general dynamics in san diego. these guys definitely have faith that their efforts will eventually pay off , because one day, if they are right even 200 years from now, fusion power would bring a new era for mankind. an era where solar and wind power are laughed at, and where petroleum and coal just cannot compete at producing the same amounts of power. it would bring a new age. bronze, steel, coal, petroleum---the age of fusion would be hard to imagine.
bewertow
4.7 / 5 (13) Apr 23, 2012
Physicists see solution to critical barrier to fusion
I would rather say, the physicists do perceive the nearing competition of cold fusion nervously and they're playing for time before publics. Because the first successful application of cold fusion would wipe their useless research completely and undeniably. They had no practical results with it during last fifty years - so why we should expect the turnover right now?


Since when has cold fusion as an energy source ever seemed plausible at all?
axemaster
4.5 / 5 (12) Apr 23, 2012
The U.S. beat the Germans at building the first atomic weapon in a two or three year period at a time when nuclear know-how was in its infancy. They should easily be able to alter or adapt equipment in short order to test the new finding.

Building a nuclear bomb is insanely easy compared to a fusion reactor. It's like comparing a caveman throwing a rock to an F-22 dropping a GPS guided bomb. Most of the time taken up by the Manhatten Project was spent refining uranium. The bomb itself was practically an afterthought.

Basically I'm saying that if you knew anything at all about fusion reactors, you'd be cringing in shame. There's a reason physicists had to develop, from scratch, the HUGE field known as plasma dynamics - the motivation was fusion. We've been working on this nonstop for over 50 years now. So please, say it's easy and stroke your ego. Meanwhile we'll actually be working on this - as we have for generations.
Telekinetic
1.9 / 5 (15) Apr 23, 2012
If I found myself spelling Manhattan as you have, I would be cringing in shame, and if a nuclear bomb was so easy to build as you've suggested, then Sri Lanka would have one. "Meanwhile we'll be actually working on this"- "we?"- you? Of all the unmitigated gall.
Skepticus
1 / 5 (8) Apr 24, 2012
"Fusion won't be viable for decades. Even if this pans out, and hopefully it will, it will still take 10-20 years just to finish experiments so that we understand how to actually go about designing a proper fusion reactor. And then another 10 years to start implementation. It's sad, I know, but it's also the truth."


The U.S. beat the Germans at building the first atomic weapon in a two or three year period at a time when nuclear know-how was in its infancy. They should easily be able to alter or adapt equipment in short order to test the new finding. It's sad, I know, but you're wrong.


You mean only when one's back is in danger of against the wall? Then, we should start stir things up for another world war...starting with Iran, perhaps? Imagine the tech advances, taking what happened during and after the last 2. Humans are at their innovative best when they are hell bent on destroying, or surviving (regrettably.)
axemaster
5 / 5 (10) Apr 24, 2012
If I found myself spelling Manhattan as you have, I would be cringing in shame, and if a nuclear bomb was so easy to build as you've suggested, then Sri Lanka would have one. "Meanwhile we'll be actually working on this"- "we?"- you? Of all the unmitigated gall.

Have you ever bothered to read any books concerning the engineering and design of nuclear weapons? I have. Did you take nuclear physics courses in college? I did. Are you a physicist? I am. I said "we" for a reason.

Most countries don't have nuclear weapons because of the difficulty in producing the uranium/plutonium for fission bombs, and because of the political problems it causes. Once you have the weapons grade material, building a bomb is quite simple. In fact I imagine that with a few weeks of work, any competent physicist could design one from scratch. Actually I don't have to imagine it, because I know people in the department who have done exactly that, just to see if they could get it right.
axemaster
5 / 5 (10) Apr 24, 2012
"Meanwhile we'll be actually working on this"- "we?"- you? Of all the unmitigated gall.

Actually I can't help but wonder, why does it surprise you so much that a physicist would be hanging around on a site called PhysOrg? What, you think we don't read anything except in peer-reviewed journals? This website is useful for keeping up with general development across multiple fields, hence why I read it.
Koen
1.6 / 5 (7) Apr 24, 2012
Philo Farnsworth claimed self-sustaining fusion reaction (with a surplus of energy) during at least 5 minutes. This claim is described in one of Farnsworth's Fusor patents. Farnsworth applied an electrodynamic type of plasma confinement that differed from the torus magnetic field plasma confinement. Nobody has back engineered Farnsworth's original fusor, but some scientists created 'similar' devices that do not show self-sustaining fusion reaction.
John_Keith_Leeper_II
2 / 5 (4) Apr 24, 2012


Since when has cold fusion as an energy source ever seemed plausible at all?


Plasma fusion is not cold fusion!
Husky
4 / 5 (3) Apr 24, 2012
The funny thing is, the sun has these bubbles and sunspots on a large scale and the plasma producing a flash, is not unlike a coronal mass ejection, i think they could take clues about the how twisting magnetic knots reconnect on the sun and take this down to the tokamak
Ian_Coleman
1 / 5 (16) Apr 24, 2012
"My understanding ... is that with any loss of power there would be a nigh-instantaneous loss of magnetic constriction and thus an immediate loss of fusion. Supposedly no radiation danger at all."

This may be true of a Tokamak, but a Tokamak is incapable of achieving 'breakeven', they require a huge input of energy to keep them running...

Any viable fusion power plant, though, must be capable of outputting energy, which will require a self sustaining plasma/fusion reaction, which won't simply shut down politely when containment fails... In principle any breach of containment will 'spill' jets of superheated plasma more than capable of flash frying large chunks of the surrounding countryside. By comparison, a conventional fission meltdown is pretty tame... For instance, if Fukushima had been a fusion plant, there'd be no Fukushima left on the map.

The moral here is don't buy into the hype that fusion power is mecessarily 'safe'...
ubavontuba
1 / 5 (7) Apr 24, 2012
I'll not be holding my breath...

Here's a cool list of various fusion methods ("breakthroughs") tried over the years:

http://www.fusor....41252795
ShotmanMaslo
1.3 / 5 (7) Apr 24, 2012
Even if we eventually work out fusion, the resulting complex fusion reactors may very well be considerably more expensive than the alternatives for a very long time to come. And the entire reactor becomes irradiated during operation. So I wouldnt hold my breath, too.
TkClick
1 / 5 (5) Apr 24, 2012
Since when has cold fusion as an energy source ever seemed plausible at all?
Since experiments like these ones. We can observe the formation of hot spots (sparks of thermonuclear reaction) at the surface of palladium electrode under infracamera. Another peer-reviewed evidence of nuclear reaction, described at NewScientist journal.
thingumbobesquire
1.8 / 5 (5) Apr 24, 2012
I think the approach here is quite promising. For decades plasma physics has been about removing impurities from these machines. This seems to be about utilizing singularities to advantage rather than eliminating them. And this appears very much to be what we see normally occurring in nature.
wwqq
5 / 5 (9) Apr 24, 2012
This may be true of a Tokamak, but a Tokamak is incapable of achieving 'breakeven', they require a huge input of energy to keep them running.


The conditions for Q ~= 1 in D-T have been achieved. D-D fusion looks possible in future designs.

[...]which will require a self sustaining plasma/fusion reaction, which won't simply shut down politely when containment fails...


Asinine. Lots of power is flowing, but very little energy is stored in the plasma.

In NIF, which is a very conservative design with far larger energy inputs than believed required for fast-ignition, we're still talking about the equivalent of a gallon of gas going *poof* if ignition is achieved.

In ITER they energy contained in the plasma will be equivalent to ~4 gallons of gas.

In less conventional designs(e.g. bussards polywell, focus fusion, general fusion...) the energy contained in the plasma is many orders of magnitude less.
Ian_Coleman
1 / 5 (11) Apr 24, 2012
"Asinine. Lots of power is flowing, but very little energy is stored in the plasma."

Question 1: How hot is the plasma? As in, what temperature?
Question 2: What does temperature actually measure?

wwqq - I'd recommend learning some actual physics before making, or more likely, I suspect, simply quoting, asinine comments yourself.
Telekinetic
1 / 5 (11) Apr 24, 2012
"Have you ever bothered to read any books concerning the engineering and design of nuclear weapons? I have. Did you take nuclear physics courses in college? I did. Are you a physicist? I am. I said "we" for a reason."-axemaster

Care to share any of your published peer-reviewed articles with us? You're a physicist like I'm a member of the President's cabinet because I'm a Democrat.
mharratsc
1 / 5 (1) Apr 24, 2012
Aneutronic fusion is getting close by the looks of it. 4 billion degree electrons was a pretty impressive milestone for the Focus Fusion team. My money's on them. ;)
Terriva
1 / 5 (7) Apr 24, 2012
here is a read about the progress of fusion research: http://hardware.s...estions. Note the graph about funding - for comparison, the cost of ITER is estimated to 17 billions of dollars. The total cost of cold fusion research is about 200 millions of dollars, i.e. roughly the cost of hot fusion research actually spent each half year.
Shelgeyr
2 / 5 (8) Apr 24, 2012
@Ian_Coleman said:
but a Tokamak is incapable of achieving 'breakeven'

That is my belief as well, for reasons too complicated to go into here. Again, I'd love to wrong.

...will require a self sustaining plasma/fusion reaction, which won't simply shut down politely when containment fails... In principle any breach of containment will 'spill' jets of superheated plasma more than capable of flash frying large chunks of the surrounding countryside.


And sadly, here's where you're wrong. I'd love to hear your support for your statement "won't simply shut down politely when containment fails", but given the nature of fusion as we understand it, the "loss of containment = loss of pinch = loss of fusion = end of reaction" chain holds true whether or not we're postulating about Tokamaks specifically.

Since no man-made fusion reactor has achieved break-even, regardless of the design, I'll admit this is just speculation.
axemaster
5 / 5 (7) Apr 24, 2012
Care to share any of your published peer-reviewed articles with us? You're a physicist like I'm a member of the President's cabinet because I'm a Democrat.

I think you have a rather warped view of what physicists actually do. Less than 50% of us actually stay in academic settings after getting our degrees - many of us work for companies and industry as "super-engineers". Many of us don't have the opportunity to publish peer-reviewed papers even if we wanted to, because we work with trade secrets and classified material (actually a TON of us work on classified stuff). To a large extent publishing is more trouble than it's worth - you have to type things up in LATEX in a very specific format, and it takes usually 20 hours or more to finish writing something up. So unless you have to do it, i.e. working in a university, there's not much reason to bother.

Just my 2 cents.
axemaster
4.2 / 5 (5) Apr 24, 2012
Although if you're interested, some of my friends have published in the last year (though I'm not sure if the papers are available online). They're chemistry guys, so I don't have much understanding of the contents unfortunately - actually I'm planning to learn chemistry as soon as I have some free time.
Shelgeyr
1.6 / 5 (7) Apr 24, 2012
@wwqq said:
The conditions for Q ~= 1 in D-T have been achieved.


Apparently I'm behind the times on this. I consider that good news, and would amend my previous statement if the editing clock had not lapsed.
antialias_physorg
3.7 / 5 (7) Apr 24, 2012
Many of us don't have the opportunity to publish peer-reviewed papers even if we wanted to, because we work with trade secrets and classified material (actually a TON of us work on classified stuff). To a large extent publishing is more trouble than it's worth - you have to type things up in LATEX in a very specific format, and it takes usually 20 hours or more to finish writing something up.

Oh boy, ain't that the truth. And 20 hours is erring WAY on the low side. 3 page conference paper and slides for the presentation is a week in my experience. Minimum.
Terriva
1 / 5 (8) Apr 24, 2012
3 page conference paper and slides for the presentation is a week
LOL, this is definitely not what the peer-reviewed means. Peer-review process itself takes months, if not years in some cases.
antialias_physorg
4 / 5 (8) Apr 24, 2012
LOL, this is definitely not what the peer-reviewed means. Peer-review process itself takes months, if not years in some cases.

I meant for typing up a conference paper. (And yes: papers for quality conferences do also go through peer review)

Going for journals (or even book chapters) takes considerably longer. The reviewing process can take months (and even years). Typing it up - and that was what he was saying - does not take years (the work that you put in to get the results sometimes does, though)

Certainly my employer won't just let me have a week off to write a paper on what I'm doing... wanting to sell the stuff before the competition gets wind of it may play no small part in this.
Ian_Coleman
1 / 5 (9) Apr 24, 2012
"And sadly, here's where you're wrong. I'd love to hear your support for your statement "won't simply shut down politely when containment fails", but given the nature of fusion as we understand it, the "loss of containment = loss of pinch = loss of fusion = end of reaction" chain holds true whether or not we're postulating about Tokamaks specifically."

Ah, yes, I understand completely... What you're saying is that plasmas in fusion reactors are somehow innately exempt from the laws of thermodynamics :-).

So with all due respect, sadly, HERE's where YOU'RE wrong... Compressing ANY gas will increase its temperature and pressure. Take away whatever's containing it, compressing it into this state, and it WON'T just meekly sit there in complete defiance of the laws of physics, because, specifically, the 2nd law of thermodynamics REQUIRES that it expand. Whether the fusion process continues is irrelevant, given enough heat and pressure, without containment, it will go off like a bomb!
Deathclock
2.3 / 5 (9) Apr 24, 2012
This may be true of a Tokamak, but a Tokamak is incapable of achieving 'breakeven', they require a huge input of energy to keep them running...

Any viable fusion power plant, though, must be capable of outputting energy, which will require a self sustaining plasma/fusion reaction, which won't simply shut down politely when containment fails... In principle any breach of containment will 'spill' jets of superheated plasma more than capable of flash frying large chunks of the surrounding countryside. By comparison, a conventional fission meltdown is pretty tame... For instance, if Fukushima had been a fusion plant, there'd be no Fukushima left on the map.

The moral here is don't buy into the hype that fusion power is mecessarily 'safe'...


No, this is stupid, fusion reactions cease once containment is lost. Do you even understand how fusion works? It requires tremendous pressure. Lose containment lose the pressure, no more fusion.
axemaster
5 / 5 (6) Apr 24, 2012
So with all due respect, sadly, HERE's where YOU'RE wrong... Compressing ANY gas will increase its temperature and pressure. Take away whatever's containing it, compressing it into this state, and it WON'T just meekly sit there in complete defiance of the laws of physics, because, specifically, the 2nd law of thermodynamics REQUIRES that it expand. Whether the fusion process continues is irrelevant, given enough heat and pressure, without containment, it will go off like a bomb!

Did you know that tokamak fusion operates under conditions of near vacuum? Now you do!

EDIT: I mean in terms of the overall volume. The chamber is pumped down, and then the remaining gas is ionized and compressed to extreme pressure by B fields. But the pressure without pinching is still very low.
nkalanaga
4.2 / 5 (5) Apr 24, 2012
Another reason it won't "go off like a bomb" is that the fuel isn't stored in the reactor. Just like an internal combustion engine, the fuel is admitted as it is used. The fuel tank may explode, which in this case would be the tank of hydrogen out back, but the reactor won't explode anymore than the average auto engine does. Blow a gasket, maybe, but that's about it.
Ian_Coleman
1.4 / 5 (10) Apr 25, 2012
"Do you even understand how fusion works?"

Only since I was 8 years old. And I've spent more than 40 years since then developing a real understanding of physics, which seems to be sadly lacking here in this forum.

"Did you know that tokamak fusion operates under conditions of near vacuum?"

Actually, yes, I did. Not for quite as long, though, since, strictly speaking, the tokamak didn't exist when I was a child, but in principle at least, a tokamak is simply a variation on the early 'stellarator' designs. As I've said from the outset, I'm not talking about the relatively tame experimental devices currently in use, but the necessarily 'scaled up' devices that are actually capable of generating any significant amount of power.

There's no point arguing, though, you'll believe what you want to believe, and having been sold the pipe-dream of 'clean, safe fusion', you won't question enough to realise that it's wishful thinking.

So what the hell. You 'win'. I wash my hands of it... :-)
AtlasT
1 / 5 (4) Apr 25, 2012

tokamak is simply a variation on the early 'stellarator' designs

Do you have some evidence for it? In accordance to common internet sources, in 1951 the Soviet physicists Andrei Sakharov and Igor Tamm designed what would later be called a tokamak (toroidalnya kamera ee magnetnaya katushka). Stellarator concept has been proposed with Lymanem Spitzer and first device has been built in 1951.

Two of the three founders of the Tokamak program have come out against the Tokamak and in June 1995, Bussard claimed in a letter to all of the plasma physics labs as well as to the relevant Congressmen, stating categorically that the tokamak program was never real -- it was just a vehicle for raising funding so that other more hopeful ideas could be trie
antialias_physorg
4 / 5 (8) Apr 25, 2012
Lose containment lose the pressure, no more fusion.

Not to mention that it requires continuous injection of fusion fuel. Unlike fission where ALL the fuel for the next few years is sitting in the reaction chamber all the time. So the potential energy content (i.e. the 'boom' factor) sitting there in a fission plant at the locus of a possible meltdown/accident is much, MUCH greater than in a fusion plant.
nkalanaga
4.3 / 5 (6) Apr 25, 2012
Even a conventional fossil fuel plant is more likely to "go boom" than a fusion reactor. Boiler explosions can be rather spectacular.
db4060
not rated yet Apr 26, 2012
The reaction is dependent upon the densities involved more so than the temperatures. Once the plasma density is no longer sufficient to maintain a fusion reaction, the plasma will then dissipate. Even in a scaled up full powered commercial unit with an output of 20 GW, the necessary containment surrounding the area containing the bottle would be more than sufficient to contain any sort of release of plasma associated with loss of field integrity.

The key is to modulate the field in such a way that these spots do not have the chance to form. If the containment field is in a constant state of fluctuation between two well defined and regulated energy states, then the possibility of a more stable reaction becomes possible. If left to find its own balance, the field will become too unstable, and the thermal variances that are being observed would be the result.
wwqq
5 / 5 (4) Apr 26, 2012
Question 1: How hot is the plasma? As in, what temperature


A few tens of keV.

Question 2: What does temperature actually measure?


Mean kinetic energy of particles.

I have touched electrons with a temperature of 546 keV(~6 billion degrees), yet I am not horribly disfigured or burned. It was a dinky like Sr-90 beta source of a few kBq, putting out some fraction of a nanowatt.

I'd recommend learning some actual physics before making, or more likely, I suspect, simply quoting, asinine comments yourself.


Dunning-Kruger effect, you're too stupid and ignorant to realize you're stupid and ignorant. Now stop posting asinine comments.
DavidW
1 / 5 (8) Apr 27, 2012
The problem with this exponential growth is that ethics needs to keep pace. The only solution is 100% ethics: "TRUTH"

Anything less than everyone accepting the Truth will result in more time for more exponential discoveries with exponential possibilities of terrible wide spread problems from not being handled ethically. The time for everyone to get on their knees and understand we are equal under the Truth is now. Anything less will not be enough.
antialias_physorg
4.3 / 5 (6) Apr 27, 2012
The only solution is 100% ethics: "TRUTH"

Lucky for us then that 'truth' is merely a philsophical concept and not something that can be attained in reality (provably, I might add).

The time for everyone to get on their knees and understand we are equal under the Truth is now.

Go ahead. If you like groveling then that's your business. Some people just have low self esteem I guess.

Me - I'll face reality on my own two feet if it's all the same to you
axemaster
5 / 5 (4) Apr 27, 2012
The time for everyone to get on their knees and understand we are equal under the Truth is now.

You forgot to mention what the "Truth" was...
Cave_Man
1 / 5 (4) Apr 28, 2012
Well, nobody will see this on the 3rd page of crazy comments but here it is anyway:

I always envisioned tiny packets of Y shaped nano channels on a 2d substrate like graphene.

Some type of preloaded fuel packet, possibly highly reactive chemicals, would be channeled into the intersection of the Y nano channels by some small ignition. Upon arriving at the intersection the fuel would be energized via an external source and the resulting physical proximity and resulting instant of plasma would be enough to produce fusion in a way that could be harvested for further ignitions as well as excess power.

Then the small nano fuel packets could me manufactured en masse. A decent amount of tech exists right now to start work on it, it would take quite a bit of effort to pioneer it and not to mention a bad business model because money would be obsolete.
DavidW
1 / 5 (9) Apr 28, 2012
The only solution is 100% ethics: "TRUTH"

Lucky for us then that 'truth' is merely a philsophical concept and not something that can be attained in reality (provably, I might add).

If you drop a ball, it happened. You can't change that and neither can anyone else. That's Truth proved. Now what?
The time for everyone to get on their knees and understand we are equal under the Truth is now.

Go ahead. If you like groveling then that's your business. Some people just have low self esteem I guess.

Me - I'll face reality on my own two feet if it's all the same to you

DavidW
1 / 5 (9) Apr 28, 2012
The only solution is 100% ethics: "TRUTH"

Lucky for us then that 'truth' is merely a philsophical concept and not something that can be attained in reality (provably, I might add).

For as long as you can. The Truth doesn't go away. You are smart guy, but I don't think you realize it's going to be a lot worse than being hit by train, again and again, until we all get Truth exists and is literally our Master. I've witnessed enough to understand this. You esteem point was not even close. Misunderstands happen.

If you drop a ball, it happened. You can't change that and neither can anyone else. That's Truth proved. Now what?
The time for everyone to get on their knees and understand we are equal under the Truth is now.

Go ahead. If you like groveling then that's your business. Some people just have low self esteem I guess.

Me - I'll face reality on my own two feet if it's all the same to you


Deathclock
1.6 / 5 (7) Apr 29, 2012
The time for everyone to get on their knees and understand we are equal under the Truth is now.

You forgot to mention what the "Truth" was...


My money's on Jesus...
wealthychef
3 / 5 (2) Apr 29, 2012
Then all of the objections to electric cars would be silenced


As they exist now, the source of power for electric cars isn't the only issue with them, so I disagree. The manufacturing of the batteries themselves is still environmentally unfriendly.


Actually, if we get fusion working, we can then use the energy to create fuel from CO2 out of the air similar to photosynthesis but more directly. This could be carbon neutral and let us keep burning fossil fuels without as much harm to the environment.