reddit: We are nuclear fusion researchers, ask us anything

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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tomschuring
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reddit: We are nuclear fusion researchers, ask us anything

Postby tomschuring » Fri Mar 02, 2012 2:27 am

from :reddit AMA series

"Hello r/askscience,
We are nuclear fusion scientists from the Alcator C-Mod tokamak at MIT, one of the US's major facilities for fusion energy research.
But there's a problem - in this year's budget proposal, the US's domestic fusion research program has taken a big hit, and Alcator C-Mod is on the chopping block. Many of us in the field think this is an incredibly bad idea, and we're fighting back - students and researchers here have set up an independent site with information, news, and how you can help fusion research in the US.
So here we are - ask us anything about fusion energy, fusion research and tokamaks, and science funding and how you can help it!

http://www.reddit.com/r/askscience/comm ... ar_fusion/


interesting read.

Betruger
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Postby Betruger » Fri Mar 02, 2012 3:38 am

In general though Tokamaks are a proven technology - we have impressive and optimistic results which look good and we can extrapolate that to larger tokamak vessels and expect success. Whereas there are a whole host of relatively immature technologies such as Focus Fusion, General Fusion, Polywell etc. and even the more mainstream Inertial Confinement experiments aren't as mature.

...
Regarding Todd Rider's thesis - he worked on both thermally-equilibrated and highly nonthermal distributions. The takeaway in either case: P-B11 fuel would bleed off a lot of its energy due to Bremmstrahlung losses, more in fact than it produces from fusion (by a factor of around 1.75, as I recall). A nonthermal distribution would reduce this factor, as a greater fraction of your distribution could actually fuse (in a thermal distribution, it's really just the high-energy "tail" of the Maxwellian that fuses), but it's still over-unity (something around 1.2 for P-B11). Add to that the requirement of energy input to maintain the nonthermal equilibrium, as the plasma will relax very quickly to a thermal distribution, and you run into problems. This effectively kills concepts like a polywell or fusor, which require active maintenance of the nonthermal distribution. A focus device, which is essentially just a magnetic-pinch implosion, could potentially avoid that maintenance problem.
As it is, the tokamak has demostrated consistently good performance, but since things like focus fusion are (a) built on a much smaller scale and (b) often privately funded, I can't think of a good reason not to research them as well - I certainly won't hold a grudge, because hey, we'll be making fusion work.
I think it is right that ITER and the experiments supporting ITER (such as Alcator) get the lions share of the funding when the evidence leads us to believe they are the most successful.
this leads us to the problem we're hitting for current budgets - if you take a look at our site here you can see ITER's funding basically eating the domestic program. ITER is the best bet we have moving forward in fusion, but the loss of our domestic program would cripple our ability to produces scientists in the future working on these projects, and would throw away a half-century's worth of technical expertise designing, building, and operating these machines. Once that's gone, you don't get it back - basically, we're deciding now whether we want to be selling fusion power plants, or buying them.

Skipjack
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Postby Skipjack » Fri Mar 02, 2012 3:41 am

I wished Rider had never written his paper. EVERYONE quotes it.

ladajo
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Postby ladajo » Fri Mar 02, 2012 3:46 am

The right answer is to go argue it. To often, folks plant a Polywell in the smae bucket as a Fusor, and if not that, then they just make the sweeping "Rider said it won't work" without actually thinking it through, or checking (the limited for sure) counter-argument work.

Miley and Bussard, as well as Nebel have made good arguments against Rider's thoughts, but the papers are not mainstream.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

Betruger
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Postby Betruger » Fri Mar 02, 2012 3:58 am

It's still surprising to see these supposedly earnest pros dismiss e.g. Polywell like that.

Skipjack
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Postby Skipjack » Fri Mar 02, 2012 4:05 am

I also find it funny that the tok fanboys dont mention the FRC work by Slough and Rostoker. I think they have a much higher chance of having a practical reactor within the next 10 years than the tok guys do.

ladajo
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Postby ladajo » Fri Mar 02, 2012 4:08 am

They currently have a vested interest. Survival.

They do not want to think there may be a better way.

It makes me feel ill to see guys completely glossing over the cost issue for viable Tokamak. "It is our best bet". They should say, "Everyone pretty much agrees it will eventually work, but it will never be a cost viable solution to global energy. However, it is gonna be The Best Toy Ever for Physicists to play with!"
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

Betruger
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Mature money muncher

Postby Betruger » Fri Mar 02, 2012 4:50 am

Yeah no kidding. So mature it's still not nearly done after so many billions.

Joseph Chikva
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Postby Joseph Chikva » Fri Mar 02, 2012 5:35 am

Skipjack wrote:I also find it funny that the tok fanboys dont mention the FRC work by Slough and Rostoker. I think they have a much higher chance of having a practical reactor within the next 10 years than the tok guys do.
How to explain you that within the next 10 years Tokamak approach does not allow to build practical reactor? As there is no any way (from using now three ways) allowing plasma heating till ignition temperature. As if temperature of plasma is lower than certain limit, plasma reactivity is too low. And today neutral beam injection is considered as main heating way. But dividing plasma internal energy required for ignition on neutrals’ injection power in real projects we will get estimation of time necessary for heating. And I estimate this time for e.g. ITER as tens seconds order. And recall that this is in case of 100% heating effeciency when 100% of input goes on heating!

Polywell as well has rather long history. 7 ! generations of experimental reactors have been built till now. Nevertheless I do not see any mention of real progress.

Rostoker is financed from private fund. And budget cut is less interesting for him. And we can see progress or failure of his approach I think in near two years.

I also doubt in Slaw's approach. As I can not see any forces enough for stopping two very small colliding plasmoids.

bennmann
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Postby bennmann » Fri Mar 02, 2012 6:28 am

Mad respect to any fusion researcher...

however tok guys drank the kool-aid every single one when they saw $$$ and ITER.

For non-native speakers, I apologize.

EIDT: If Park did one of these AMAs, I would have to change my pants.

Robthebob
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Postby Robthebob » Fri Mar 02, 2012 6:48 am

I dont know if I can stand the whole "Rider Paper said it wont work" argument anymore. Doesnt it only say things about fuel types? Polywell works on D-D or D-T...

The whole thermalization question has plagued us from the start, isnt this fairly easy to investigate? I would think emc2 corp, before they do anything else, would look at if the machine thermalize, if it does, then that's it, nothing else to look at.

Maybe it's wishful thinking, but the fact that they're still doing work on it, I honestly feel like there's more to it than what we can see on the surface.
Throwing my life away for this whole Fusion mess.

Joseph Chikva
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Postby Joseph Chikva » Fri Mar 02, 2012 8:06 am

bennmann wrote:Mad respect to any fusion researcher...

For non-native speakers, I apologize.
One question from non-native speaker.
Why not respect to any researchers?
What do you think; fusion researchers are smarter than those who develop e.g. new materials? For example new type of rubber for condoms.

Skipjack
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Postby Skipjack » Fri Mar 02, 2012 3:52 pm

Joseph Chikva wrote:How to explain you that within the next 10 years Tokamak approach does not allow to build practical reactor?

Reread what I said. My point was that Toks will NOT be able to do it in 10 years, but IMHO FRC- colliding beam reactors will be possible within the same timeframe, provided they get enough funding. So you were lecturing me the very same thing that I said ;)

D Tibbets
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Postby D Tibbets » Fri Mar 02, 2012 4:24 pm

The problem with Riders conclusions as possibly applicable to Polywells, is that, while he may have considered both thermalized plasma and mono energetic plasma, he did not consider the energy distribution of the electrons. Cold in the center and hot on the edge. Also, I don't think he considered a dillute concentration of boron. Perhaps ~ 10 protons for each boron. I'm uncertain how this would effect the fusion rate (at the same total density), but it would significant decrease the Bremsstrulung.


As Bremsstrulung scales as ~ 1.75power of the temperature of the electrons, and the square of the Z, the Z component of a 1:1 mixture would be ~ 1^2 + 5^2 or ~ 26. For a 10:1 mixture (at the same total density) it would be ~ 2* ( 1 ^2))+ (0.1* (5^2) = ~ 2+ 2.5 = ~ 4.5. This would be ~ 1/6th of the Bremsstrulung. This by itself would allow for a positive Q provided the fusion rate doesn't change too much.
The cold in the center electrons allow for additional gain such that some (M. Simon among them) have calculated that a positive Q of ~ 5-20 may be possible. with P-B11 fusion in a Polywell.

In a DPF the Bremsstrulung would not have the cold electrons in the center advantage. Instead, if it works it will use Bremsstrulung suppression at very high magnetic field strengths, and high efficiency X-ray energy recovery mechanisms. I understand that this might allow for final power generation gains of ~ 3-5X.

Also, I don't know if Riders X-ray losses calculation were raw numbers or if they included energy recovery through a thermal steam cycle. ~ 30% of the X-ray losses would be possible with a steam cycle. The DPF may be able to harvest much more (~80-90%?) . I don't know if a Polywell could harvest the x-rays as well.

In any case, the Bremmstrulung issue is much more benign with D-D fusion, which has some advantages over over DT fusion. And the Polywell could also gain efficiency by burning the produced tritium and/ or Helium 3. And of course D-D burning Polywells can provide the He3 for a separate D-He3 burning Polywell where aneutronic fusion(<1% fusion energy as neutrons) and perhaps some moderate efficiency direct conversion is desired.

I don't know if a DPF could survive long enough with D-D fusion because of the high neutron flux in these small machines.

Most of the above (except the cold core electrons?) may apply to the FRC also.

My limited understanding of Tokamaks is that positive Q fusion is probably obtainable. The problems may be the diverter and tritium production requirements. And, the size and associated costs may end up being the biggest road block to commercial Tokamak development.

Dan Tibbets
To error is human... and I'm very human.

Joseph Chikva
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Postby Joseph Chikva » Fri Mar 02, 2012 5:25 pm

Skipjack wrote:
Joseph Chikva wrote:How to explain you that within the next 10 years Tokamak approach does not allow to build practical reactor?

Reread what I said. My point was that Toks will NOT be able to do it in 10 years, but IMHO FRC- colliding beam reactors will be possible within the same timeframe, provided they get enough funding. So you were lecturing me the very same thing that I said ;)
And I said that I could not found explanation how very small plasmoid can stop each other that is needed for merging. And, so, I do not believe in viability of this approach too.
Another issue if small plasmoid collides large volume of background plasma. In this case yes majority of kinetic energy transfers into thermal.


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