EMC2 has published a polywell preprint on arXiv

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

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Tom Ligon
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Re: EMC2 has published a polywell preprint on arXiv

Postby Tom Ligon » Fri Jun 06, 2014 6:43 pm

Todd Rider's objections were not just for the Polywell, but for hot fusion generally. The heart of his objections are essentially that everything will thermalize and spew bremsstrahlung radiation. Dr. Bussard could never get thru to him and quit trying. If Rider is right, no fusion project will ever work.

The continued sincere efforts my multiple research efforts suggest that a lot of good people in the field disagree.

And Rider is NOT in the field. Nor should he be. He's a clever enough person and is making good contributions in his chosen field. Good thing his chosen field is NOT fusion, since it would be a real downer to spend a career working on something you think is folly.+

http://www.businessweek.com/magazine/todd-rider-has-a-kill-switch-for-viruses-11032011.html

mvanwink5
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Re: EMC2 has published a polywell preprint on arXiv

Postby mvanwink5 » Fri Jun 06, 2014 6:48 pm

Ok, who's ready to build a 1 meter radius 7T Polywell, raise your hand? The only other thing to do with WB-8 is to build WB-8.1 just to check out PB-11.
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

D Tibbets
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Re: EMC2 has published a polywell preprint on arXiv

Postby D Tibbets » Fri Jun 06, 2014 7:25 pm

I admit to some confusion. I wonder about previous results and their validity. The simplest solution is to emphasize the instrumentation of this machine that allowed for actual measurement (X-ray emmision), that given the machine setup can only be explained by the energetic electron containment consistent with high Beta conditions. No if's and or buts...

There is a whole can of worms about building up to Beta=1 conditions, but as this demonstrates, Parks, etel managed to do it in this machine unequivocally. Criticisms about the Wiffleball effect validity is answered.

As for neutron production with D-D, it is perhaps the simplest measurement, but there are caveats. It only gives the fusion rate. It is not a direct measure of confinement or Beta=1 conditions. It is a result that might be consistent with a set of parameters, but pinning down the individual contributions is problematic. And if as in this machine, things happened over a few dozen micro seconds, it might be difficult to get an accurate time scale for the neutron production. That was a problem with WB6, there was some neutrons produced, but the time slice sensitivity of their neutron counter was only ~1 millisecond. It was assumed that the production was during the ~ 0.25 seconds of claimed high beta conditions, but not proven. I don't know how short of sampling times are available in the best neutron counters, but a few microseconds is not long.

One head scratcher is the D-T reactor example given. At 60 KV with an assumed 50% potential well ion acceleration efficiency giving an ~ 213 MW input energy and a fusion cross section of 1.2 barns, the yield was 1.9 GW. The center of mass energy given as 30 KeV (which reflects 50% potential well conversion efficiency). But, this would assume beam- target dominance. If beam- beam, only 1/2 of the accelerating voltage would be needed, thus input would be only ~107 MW and Bremsstruhlung would be only ~ 1/4th of the reported number. Actual beam- beam vs beam- target fusion would probably be some at some intermediate value. And, then you have to pay attention to the current and voltage needed to maintain the Beta=1 condition. Also, at 30 KeV the D-T fusion cross section curve seems to indicate a cross section of ~ 3-4 barns, which is 2-3 times that of the value used*. Then there are questions about the thermal spread of the ions, and any central confluence. Also, what Wiffleball confinement value did he use? Is 300 relevant for this extrapolation? This machine served its purpose, but it did have compromises. The most obvious is the B field measuring coaxial cables penetrating the machine interior. And 7 Tesla may be a fairly conservative target. And, ...

I take this prediction to be a conservative estimate, based on unfavorable or neutral assumptions, once the basic Wiffleball status is accepted. Actual performance may be better, or even much better than this. As such, this is a wake up call to the fusion community used to thinking of tokamaks.


* If fuel burn up over the lifetime of the fuel ions is already near 100 %, using the higher cross section value may be moot. Electron confinement is a different matter, and other issues may be changed though.

Dan Tibbets
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hanelyp
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Re: EMC2 has published a polywell preprint on arXiv

Postby hanelyp » Fri Jun 06, 2014 8:16 pm

Skimming the 1406.0133 paper, I see a problem in figure 1b not showing the modification on magnetic field lines from plasma pressure.
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DeltaV
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Re: EMC2 has published a polywell preprint on arXiv

Postby DeltaV » Fri Jun 06, 2014 10:02 pm

To me the figure looks notional/schematic, not intended to accurately show field distortions. But I would still prefer the 3D wiffleball picture seen elsewhere.

@MSimon: Pinged Alan Boyle?

MSimon
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Re: EMC2 has published a polywell preprint on arXiv

Postby MSimon » Fri Jun 06, 2014 10:23 pm

DeltaV wrote:To me the figure looks notional/schematic, not intended to accurately show field distortions. But I would still prefer the 3D wiffleball picture seen elsewhere.

@MSimon: Pinged Alan Boyle?


I'll send him an e-mail - thanks for the heads up.
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mvanwink5
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Re: EMC2 has published a polywell preprint on arXiv

Postby mvanwink5 » Fri Jun 06, 2014 10:28 pm

So, EMC2 figured out the trick to make polywell work is to pop the clutch, slam the polywell full of electrons and ions so that the cusps close before too many ions escape through the cusps and cause an arc. Jump right to beta = 1. Who would have thought of that ahead of the actual experimental work?

Congratulations EMC2!
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

DeltaV
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Re: EMC2 has published a polywell preprint on arXiv

Postby DeltaV » Fri Jun 06, 2014 10:33 pm

http://www.talk-polywell.org/bb/viewtopic.php?f=10&t=468&p=4940#p4940

rnebel wrote:The best analogy that I can think of is that the wiffleball mode is the jet engine and the ion convergence is the afterburner. The 2.5e22/m**3 density is what the Polywell should have on the edge, and then it hopefully goes up a few orders of magnitude as it goes into the interior. I don’t mean to imply that ion convergence isn’t important. This power density boost is what enables the Polywell to be built in small attractive unit sizes and to easily use advanced fuels.
However, the wiffleball mode is essential and the ion convergence simply makes things better. If we can’t get the wiffleball, then we can kiss our behinds goodbye. That’s why we are focused on achieving the wiffleball and we aren’t paying any attention to Rider and Nevins. They’re just a distraction.

Fig. 5 in the paper shows about 1e16/cm**3 = 1e22/m**3 for bulk electron density at 700MW peak input power. Smaller magrid.

djolds1
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Re: EMC2 has published a polywell preprint on arXiv

Postby djolds1 » Fri Jun 06, 2014 11:35 pm

hanelyp wrote:Skimming the 1406.0133 paper, I see a problem in figure 1b not showing the modification on magnetic field lines from plasma pressure.
There are also the five videos.
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mvanwink5
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Re: EMC2 has published a polywell preprint on arXiv

Postby mvanwink5 » Sat Jun 07, 2014 12:08 am

Anyone find links to the movies?
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

MSimon
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Re: EMC2 has published a polywell preprint on arXiv

Postby MSimon » Sat Jun 07, 2014 12:17 am

Engineering is the art of making what you want from what you can get at a profit.

choff
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Re: EMC2 has published a polywell preprint on arXiv

Postby choff » Sat Jun 07, 2014 3:45 am

Maybe it's time to send the article link to Art Carlson and get his take on it.
CHoff

D Tibbets
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Re: EMC2 has published a polywell preprint on arXiv

Postby D Tibbets » Sat Jun 07, 2014 4:39 am

The 700 MW seems a huge number, but remember the ambiguity of the Watts unit. With the plasma gun injection occuring over ~ 7 micro seconds, the energy input is 700MW *0.000007 s =~ 5000 Joules. This is a moderate amount of energy. The key componete is the time frame. The energy input needs to exceed the energy leakage (and Bremsstruhlung cooling) at the cusp confinement conditions before Beta can be increased. Apparently in the WB8 machine, and possibly WB7 versions, this input could not be aschieved or maintained long enough. Thus the back door approach of using a plasma gun to inject relatively cool plasma, but at a high intensity. Based on the x-ray filters that cut off X-ray Bremmstruhlung emmision below ~ 2000 eV, the plasma gun output was below this voltage. Thus only the density of electron gun beamed electrons contributed to the measured X-ray output. This results in only the high energy electron gun injection efficiency and dwell time (high energy electron confinement) contributing to the measured x-ray intensity and duration. That the duration was not steady state reflects the inadequacy in the high energy electron injection quantities to maintain the density (and energy)against losses, combined with the losses of the initially lower energy electrons and ions from the plasma gun. thus the Beta +~1 was established, but could not be maintained. As the Beta dropped somewhat, the confinement dropped even faster, so that confinement reverted back to cusp confinement exponentially. So, a brief plateau is not unreasonable under these conditions.

From the graphs, the signal to noise ratio was essentially 1 or unmeasurable at the cusp confinement, so the actual magnitude of the increase is difficult to quantify, but that there is a significant difference is obvious, and represents a minimal differential as the actual baseline is buried in the noise. The results at a lower B field strength is interesting and I have some vague ideas about what is going on, but my impression may not stand up to closer inspection.

The decreased cusp confinement reported in this machine is 1/5th to 1/ 10th that claimed for WB6. But the reduced size, and the apparent greater relative magnet separation, and the previously mentioned invasive coaxial cables used to measure B field strength may account for this difference. The B field sgtrength versus the amp turns relitive to WB6 is confusing for me. Also, without apparent positive potential on the Magrid, recirculation may be much different. The apparently poor cusp confinement reported is perhaps explained, and the important point of ~ 40 fold relative improvement with Wiffleball / Beta-1 confinement conditions is consistent.

It is impressive to me that this machine , even at its small size and modest B field strength was able to achieve densities of ~ 10^21 charged particles per cubic meter. Thus, not only high Beta/ Wiffleball confinement was demonstrated, but also densities that allow for useful fusion output in small machines.

Dan Tibbets
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TallDave
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Re: EMC2 has published a polywell preprint on arXiv

Postby TallDave » Sat Jun 07, 2014 7:51 am

Yeesh, 1.6GW net power output for a 1 meter radius? Did I read that right? It's late, must sleep...

That's probably optimistic but it's still an encouraging estimate given that they've done some scaling now. That means it should cost around $200M (vs $20B for ITER which is planned to produce 500MW). That's the power of high beta!

I recognize Skillicorn's name (along with Krall and Park of course). Good to see the band is still together. Hard to believe it's been seven years. I hadn't even met my wife yet, now I have two kids.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

Betruger
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Re: EMC2 has published a polywell preprint on arXiv

Postby Betruger » Sat Jun 07, 2014 11:22 am

If only Doc B. could see this..
You can do anything you want with laws except make Americans obey them. | What I want to do is to look up S. . . . I call him the Schadenfreudean Man.


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