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

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KitemanSA
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Postby KitemanSA » Sat Feb 04, 2012 11:49 am

Roger wrote: If I'm following correctly....
I would expect that any design that removed nubs would remove some loses? No?
There is no real need to REmove the nubs, just move them into a more shielded area away from the line-like cusps.

mvanwink5
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Postby mvanwink5 » Sat Feb 04, 2012 5:03 pm

D Tibbets wrote:..... the nubs reduced ion containment, and perhaps electron recirculation, and yet their elimination resulted in greater density, which implies better ion containment and also electron confinement/ recirculation. This would seem to indicate that less electron injection power would be needed. But this applies only if the density is a constant. If the density increases proportionately greater than the input savings, the net result would be greater input needs. Another way of saying this (I think) is that is they cranked the electron injection to the maximum the supply could deliver, and anticipated a density of X and a Beta of 0.99, they may have gotten a density of X*1.5 or 2 and a Beta of 0.9. There would be room for even better performance if they get more power in order to hit the adjusted target of Beta=0.99.


Dan, although you have some reservations with this reasoning, it does seem to fit with what EMC2 has said up to now. Also, what HappyJack has pointed out and has modeling to support, better confinement will also make it harder for recirculating electrons to return, and make it more demanding on the electron injectors to inject the electrons. I am not sure if there is a trade off that gets worse with scale, if just increasing cusp size with scale would counter a bad trade off, or what. Only actual lab testing can tell. I would guess that the answer is promising and reaching for the higher beta in this quarter with the new electron guns would point to this.

Thanks for your thoughts, and
Best regards
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

rjaypeters
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Postby rjaypeters » Sat Feb 04, 2012 5:06 pm

@KitemanSA,

Something like this:

Image

or this?

Image

Since there should be pretty symmetric forces (except for gravity), we might be able to use only two diametrically opposed cantilever supports per coil.
"Aqaba! By Land!" T. E. Lawrence

R. Peters

rjaypeters
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Postby rjaypeters » Sat Feb 04, 2012 5:37 pm

Having only two supports doesn't look so pretty with this one:

Image

But this arrangement is tetrahedral:

Image
"Aqaba! By Land!" T. E. Lawrence

R. Peters

RobL
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Postby RobL » Sat Feb 04, 2012 6:14 pm

Two supports must be a better solution than three or four due to the reduced total area to prevent ions and electrons hitting, as well as less area to cool. Each of the two supports will be less than 40% thicker than 4 supports would be to carry the same current and coolant with proportionally less insulation and shielding thickness.

As they are carrying twice the current there will be a higher than 40% increase in their surface B-field and so improvement in their effective magnetic shielding.

The problem with just 2 supports is that there will be substantial side forces on them, working to push the coils to one side, and with the Polywell coils being in an only marginally stable configuration that could lead to pretty catastrophic behaviour if they started to tilt over.

KitemanSA
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Postby KitemanSA » Sat Feb 04, 2012 7:41 pm

Personally, I don't think any of those designs protect the legs from the fields. The electrons exit the cusps and follow the field lines around until they impact the legs.

I'm thinking more like this though if you want to keep the magnets to 6, the corners around the triangles can be much thinner and even more removed from the square plan form magnet corners. Also, the 4 legs can be much thinner too. In this way, ALL the metal (or almost all) cn be protected by magfield.
Image

Roger
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Postby Roger » Sat Feb 04, 2012 9:20 pm

[quote="D Tibbets]Yes and no. [/quote]

Thanks.

Isnt EMC2 using a beveled magnetic ring, I see a lot of graphics above showing tubluar rings.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

happyjack27
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Postby happyjack27 » Sat Feb 04, 2012 10:53 pm

mvanwink5 wrote:
D Tibbets wrote:..... the nubs reduced ion containment, and perhaps electron recirculation, and yet their elimination resulted in greater density, which implies better ion containment and also electron confinement/ recirculation. This would seem to indicate that less electron injection power would be needed. But this applies only if the density is a constant. If the density increases proportionately greater than the input savings, the net result would be greater input needs. Another way of saying this (I think) is that is they cranked the electron injection to the maximum the supply could deliver, and anticipated a density of X and a Beta of 0.99, they may have gotten a density of X*1.5 or 2 and a Beta of 0.9. There would be room for even better performance if they get more power in order to hit the adjusted target of Beta=0.99.


Dan, although you have some reservations with this reasoning, it does seem to fit with what EMC2 has said up to now. Also, what HappyJack has pointed out and has modeling to support, better confinement will also make it harder for recirculating electrons to return, and make it more demanding on the electron injectors to inject the electrons. I am not sure if there is a trade off that gets worse with scale, if just increasing cusp size with scale would counter a bad trade off, or what. Only actual lab testing can tell. I would guess that the answer is promising and reaching for the higher beta in this quarter with the new electron guns would point to this.

Thanks for your thoughts, and
Best regards


i've given this some thought, and i think if you hold the magnetic field strength constant while scaling up the size of the machine, you can increase the fusion yield without a proportional increase in the amount of electrons you have to put in. so therein, seems to me, lies the somewhat couter-intuitive solution: at some point you stop scaling up the magnetic field strength, but continue to scale up the radius. energy to replace loses will grow in proportion to r^2 (surface area of a sphere), whereas fusion yield will grow at least in proportion to r^3 (volume of a sphere). so your scaling laws aren't nearly like the miraculous r^7 (which was largely from the mag field strength), but they're still - i dare say - better than a tokamak.

TallDave
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Postby TallDave » Sun Feb 05, 2012 4:03 pm

93143 wrote:Ambipolar, not bipolar.

...

Also, if my 'Langmuir onion' multiple-well concept is correct, the MFP only needs to be on the order of the plasma wavelength, not the machine size.

Or I could be out in left field... maybe I should do some actual math on the concept someday...


Maybe we can get Joel to simulate that. My wild guess that it will match experimental data the most closely.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

TallDave
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Postby TallDave » Sun Feb 05, 2012 4:11 pm

During 4Q of 2011, EMC2 has modified the electron injectors to increase the plasma heating. The higher plasma density in WB-8 prompted the need for higher heating power. We plan to operate WB-8 in high beta regime with the modified electron injectors during 1Q of 2012.
At first glance I said "Oooh, that sounds really bad." And it may be -- it suggests losses were higher than expected.

But then thinking about how the wiffleball inflates and looking at their wording, I wonder if that just means they couldn't get to the high-beta regime where the losses fall off, which is somewhat less worrying. There must be levels of electron injection at which the losses reach the injection levels before inflation to the high-beta regime is achieved, though it's somewhat worrying that they apparently did not correctly predict the necessary power, which might say any of a number of things about the WB loss curve (but not necessarily bad things). Of course, the WB is a pretty new phenomenon anyway, I guess that shouldn't be a surprise.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

choff
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Postby choff » Sun Feb 05, 2012 8:00 pm

Possibly they found the confinement so much better than expected that they decided to try operating at a higher power level?
CHoff

D Tibbets
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Postby D Tibbets » Sun Feb 05, 2012 10:21 pm

Nubs vs wall standoffs has been argued in old threads. I suggested a highly arching nub (shaped like a long U). This would approach the characteristics of wall standoffs, but there was questions raised about the strength of such supports. Irregardless of nubs being present between magnets, there has to be at least one set of wall standoffs in order to hold the magrid in the center of the vacuum vessel. The advantages of supporting each magnet in this manner is that there is more plumbing for coolant flow. They may also allow a skeleton for mounting direct conversion grids. Each magnet can be cooled in parellel against the Bremsstrung, possible ohmic , and leakage (ExB drift) generated heat; instead of all six or more magnets needing to be cooled serially with one coolent flow. The loss considerations may take a back seat to these other issues.

As for concentrating on size scaling while maintaining a modest B field, Joel Rogers has basically simulated this with his modest B field assumptions two years ago. The resultant size was well over 100 meters diameter, though other issues may change this (like the drive voltage, and other assumptions and predictions of the sim).

In general, the more you can push the B field the better. The output power scales much faster with increasing B field. If it takes 300 MW to start up a 1 GW Polywell, it would put restraints on the application, especially on ships, etc, where start up power may need to come from an axillary generator. A 10 MW start up input with 50 MW output capacity would be much more attractive.

Then there is the construction costs which may scale at ~ the cube of the diameter.

On the other side are engineering issues. If wall thermal loads limits the size, then this will be the final consideration on machine size at any given output power. There would be little point in increasing B field past this point(?).

On the other hand, vacuum pumping capacity may be the limiting issue. Both density and volume are important, and this may limit the smallest practical size and target B field strength... or it might limit the largest possible size.

I can envision a ship or spacecraft system consisting of two reactors. The Startup reactor may be small and optimized for minimal needed start up power input , and this provides the start up power for a more powerful reactor that is optimized for maximal power output over long durations. The ability to widely throttle one or both reactors would also be attractive.

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

D Tibbets
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Postby D Tibbets » Sun Feb 05, 2012 10:41 pm

I'll add, again, that all of this speculation may be moot. The issue as mentioned may be merely increased voltage capacity. This would be useful for multiple reasons. But, the most optimistic assessment is that they may be preparing to test P-B11 reactions. If successful, they may wish to go directly to a P-B11 demo, and abandon D-D efforts. This may have time, cost, proliferation, etc advantages. Also, in parellel, it would drive a persuit of direct conversion technology.
It would be similar to jumping from the Tokamaks of the 1970's straight to ITER. If their confidence and/ or urgency is great enough.

Um...
I doubt there is much urgency in the overall energy community. Rather that it will take extraordinary evidence to dislodge the inertia of other fields of energy research and production. There may be justification for a Hail Mary pass. Then again, it may be desperation time. Perhaps the most boring assessment is that it is merely anticipated evolution of their research. This is boring because it would perpetuate the current low level of transparency in the research.

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

bennmann
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Postby bennmann » Mon Feb 06, 2012 6:43 pm

This is boring because it would perpetuate the current low level of *public transparency in the research.

mvanwink5
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Postby mvanwink5 » Mon Feb 06, 2012 8:08 pm

As earlier posted and as I see it, dropping the wording of directing their tests at determining scaling, points to scaling now being understood (scaling was mentioned in the two previous reports and is not mentioned now). Further, I would also posit that if the scaling was unacceptably low, more testing would be in order to see if there were variables that would improve the scaling, as scaling is everything for WB-8. In fact, determination of scaling is the whole reason for the WB-8 project.

Regarding the theoretical speculating about the use of the word heating, I think it is worth pointing out that the words heat and energy have been used interchangeably in past reports. It makes me wonder somewhat who is writing these brief reports, or if this is just some polywell group-speak that has leaked into the report (electric utility people and Navy people should be aware of terminology that is used internally that would baffle others), or just post bureaucratic editing.

Regarding B11 testing, boring or not, that is in the cue for the next WB-8 round of tests after this, so no speculation there other than if it will happen.

In summary, if scaling is understood at this point, I would expect this to be the final report and it is marked as being the final report. Also, needing more powerful electron guns at this point should be seen as quite positive when taken together with confinement having been remarked at as being excellent and the pursuit of higher plasma density. That is my opinion of course as is everything else above.
Best regards

(edited for clarification)
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.


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