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

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D Tibbets
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Post by D Tibbets »

Brian H wrote:
D Tibbets wrote: ...
Given efficient x-ray energy recovery and some solution to rapid cathode erosion, the claimed Q of ~ 1.8 would be the greatest economic limitation. Given 80% conversion of fusion charged particle energies and bremsstrulung x-ray energy recovery means that for every 1 MW of energy input (= waste heat) there would be ~ 1.5 MW of usefull electrical output. The machines are small, but with the ~ 500 KW of excess power out you would have to cluster alot of machines to generate ~ 100's MW powerplant outputs....

As has been mentioned, a DPF, even at much lower efficiencies would make an excellent neutron source for a fusion/ fision hybird plant (using D-D as the fuel). It may have cheaper life cycle costs compared to a larger FRC system, and it's small size (without the X-ray shield) might be ideal for embeding within a fission structure...
Dan Tibbets
The cooling of the electrodes is expected to constrain the power levels, which scale with the "shot" frequency; about 330Hz would probably be the sweet spot to begin with, which would generate about 5MW. The neutrons are few, only resulting from side reactions, and are slow, not fast. They will be stopped by a water/B10 shell enclosing the entire rig. No radiation above ambient is expected outside the shell.

As for electrode erosion, that would be correspondingly less, since there is no fast neutron flux. Servicing is expected semi-annually or less.
No neutron flux for P-B11 fuel, but if used as a neutron source for a fusion/ fission hybird, D-D or D-T would be used. A beryllium anode was suggested because it is mostly transparent to x-rays (not heated up as much). But in a D-D machine, the beryllium would absorb alot of neutrons (would it absorb fast neutrons?). Would it survive long under these conditions (both the thermal load from neutron impacts, and the transmutations that could occur).

As an intermittant intense x-ray or neutron source for expermental purposes, it might serve as well as the NIF laser system, but at a cost that is much less.

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

Aeronaut
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Post by Aeronaut »

Skipjack wrote:Well, I see that if they are that small, they could probably have applications in areas where larger systems can not be used?
Like heating and electricity for small communities.
This thing seems to be cheap enough for that.
Yes, that's precisely what I had in mind when I postulated a world with several aneutronic designs on the market.

The PW is well positioned for high power density applications, although I'm reading a gigantic heat dissipation challenge if it's not used to replace coal-fired boilers or melting feedstocks. It also has the capital cost difference to contend with.

The FF is ideally suited to act like a pad transformer in local transformer yards to cost-effectively absorb base load growth and keep load fluctuations localized, if purchased by utilities and municipalities.

A competing distributed deployment scenario postulates just about every corporate (read big chain building like convenience stores and french fry crinkling factories) being powered by one FF and wholesaling the surplus to the local utility for around $400/day/store extra income.

PW's greatest strengths imho are it's power density and scalability.
While FF doesn't scale (it stacks), 5MW is a nice fit for locomotives.
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zapkitty
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Post by zapkitty »

Aeronaut wrote: The PW is well positioned for high power density applications, although I'm reading a gigantic heat dissipation challenge...
Yep... I just ran the numbers for an orbital installation assuming that the PW doesn't vent waste products overboard for cooling help (if that would even help). Dealing with 20 megawatts thermal in waste heat gets gets kinda crazy when using current space hardware. The "football field" metaphor is out... maybe "runways for jumbo jets?"
Aeronaut wrote: While FF doesn't scale (it stacks), 5MW is a nice fit for locomotives.
Or for small commercial space stations...

FF meets Sundancer:
Image

A couple of Sundancer modules, three nodes, a 64 kilowatt SLASR solar array, a propulsion module opposite a station radiator, and the dedicated radiator for the FF... 800 square meters of anodized aluminum running water at 200C to handle 2 megawatts of waste heat from the FF...

... a double-sided cruciform arrangement makes it usable and folded up the radiator should fit on a Falcon 9 or EELV...

And when you use BA-330s instead of Sundancers then it gets sorta like this:
Image

4 BA-330s. Vastly more volume than ISS and still with endless power for operations... that is, if you're using ISS power standards...

And the thing is... if the efficiency of the polywell holds up then one could use the same radiator to deliver twice the power of a FF to the same station!

... assuming one could talk emc2 into building a 10MW PW...

... and also assuming that you could stuff it into a Sundancer... :)

But seriously, when spacecraft designers dare think big again then PWs should come into their own.

Aeronaut
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Post by Aeronaut »

Thinking big, those modules must have well over 800 square meters of aluminum surface that could make up for lost radiative efficiency while reducing capital expense and launch weights by eliminating the dedicated radiators.
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zapkitty
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Post by zapkitty »

Aeronaut wrote:Thinking big, those modules must have well over 800 square meters of aluminum surface that could make up for lost radiative efficiency while reducing capital expense and launch weights by eliminating the dedicated radiators.
Errr.... these are the inflatable Bigelow Aerospace modules I've been going on about in the FOOF thread... what are these "aluminum surfaces" that you speak of? :)

http://en.wikipedia.org/wiki/Sundancer
Image


http://en.wikipedia.org/wiki/BA_330
Image


... the 40cm thick walls of layered synthetics are quite a bit tougher than ISS module hulls in many respects and are much lighter to boot...

Aeronaut
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Post by Aeronaut »

You caught me living in the past with 5mm aluminum hulls, zapkitty. :shock:

Did anybody ever come up with a description of how it's shielded from cosmic radiation? The wiki editors are dieing to know, also.
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D Tibbets
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Post by D Tibbets »

Concerning the FF (DPF) reactor as a space power source. As the need for increasing power goes up the advantages of a high Q, direct conversion system like the Polywell becomes more advantagous.
But for small applications- like interplanatary probs, the small size and weight (?) of the FF might be convient. Comparing it to a radionucleotide thermal battery or reactor the FF would be cleaner (no neutrons- at least in a fission reactor, a battery might have only easily stoped radiation like alpha or beta particles). So long as it is slightly over unity, the waste heat generated could power an inefficient thermocouple system just like the radioactive battery. To provide a few hundred or thousand watts continously, it might need to fire only a few times per minute. Any direct conversion would provide most of the power , with the thermal conversion giving a small boost in efficiency and serving cooling purposes. The weight needed to convert the x-rays may be the show stopper.

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

Aeronaut
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Post by Aeronaut »

D Tibbets wrote:Concerning the FF (DPF) reactor as a space power source. As the need for increasing power goes up the advantages of a high Q, direct conversion system like the Polywell becomes more advantagous.
But for small applications- like interplanatary probs, the small size and weight (?) of the FF might be convient. Comparing it to a radionucleotide thermal battery or reactor the FF would be cleaner (no neutrons- at least in a fission reactor, a battery might have only easily stoped radiation like alpha or beta particles). So long as it is slightly over unity, the waste heat generated could power an inefficient thermocouple system just like the radioactive battery. To provide a few hundred or thousand watts continously, it might need to fire only a few times per minute. Any direct conversion would provide most of the power , with the thermal conversion giving a small boost in efficiency and serving cooling purposes. The weight needed to convert the x-rays may be the show stopper.

Dan Tibbets
FF will most likely enter production as a thermal device as the x-ray converter yields increase. I'd look for .25 to 1MW milestones as the production tooling matures. But solar cell and computer chip prices could be lowered as such CVD-based tooling evolves. (CVD is Chemical Vapor Deposition)

Just like with the PW, FFs in space apps have to justify the additional support machinery and mass. JPL funded the first 2 FF scaling experiments (for a total of $300k) to check out its potential as an ion drive.

Another factor hindering use as a universal heater is that the heat is expected to be under 800 degrees and removed by pressurized helium.

I'd bet on nuke batteries to power probes for a while.
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zapkitty
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Post by zapkitty »

Aeronaut wrote:Did anybody ever come up with a description of how it's shielded from cosmic radiation? The wiki editors are dieing to know, also.
That's easy.... almost nothing protects you from cosmic rays once you're above the exosphere.

Beyond the last traces of atmosphere it takes a couple of metric tons of water or dense polyethylene per square meter of hull to be shielded just to start to cut down on incoming GCR.

Did you mean solar radiation? That's a more immediate threat on any given journey but it's also a more tractable problem. Don't have numbers on Bigelow rad shielding.

Aeronaut
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Post by Aeronaut »

Thanx, zapkitty. I never was too clear about which types of radiation NASA thought necessary for longer voyages than the moon.
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zapkitty
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Post by zapkitty »

Aeronaut wrote:Thanx, zapkitty. I never was too clear about which types of radiation NASA thought necessary for longer voyages than the moon.
Both types are important to deep space travel but only the solar particle stuff can even be partially handled by any shielding that current spacecraft can carry.

A classic Hohmann transfer to Mars and back would have the crew exceeding their lifetime dose limits and then some just from GCR exposure alone...

... funny how most Mars first types don't mention this...

... yeah, it's one of the reasons why we're still stuck in LEO or under the lunar regolith for considering permanent space habitats.

Fusion changes that.

Just as Apollo astronauts dashed through the Van Allen belts on the way to the moon a fusion-powered ship can dash to Mars in just over a month with the crew needing to only worry about solar particle shielding... and that much shielding a fusion-powered ship can carry without hassle.

Skipjack
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Post by Skipjack »

I think they wanted to make some sort of electromagnetic shield to protect the crew. Of course that would also need a A LOT of energy.

Giorgio
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Post by Giorgio »

Skipjack wrote:I think they wanted to make some sort of electromagnetic shield to protect the crew. Of course that would also need a A LOT of energy.
Yes, there was a couple of projects funded by NASA for a moon base shielding based on electrostatic magnetic field.
One of the final reports is this:
http://www.niac.usra.edu/files/studies/ ... Buhler.pdf

I'll have to dig trough my home PC links to find the others.

Giorgio
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Post by Giorgio »


Skipjack
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Post by Skipjack »

Yeah, the second one looks very familiar.

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