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

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Art Carlson
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Post by Art Carlson »

Axil wrote:The General Fusion approach uses lead to form the compression wave that produces D-D or D-T fusion. The neutron energy that is produced exceeds 14MeV. These high energy neutrons will penetrate many tens of meters of lead (14 * 4 = 56 meters).
There's got to be a mistake in there. This document lists "Typical blanket module dimension (Inboard equator)" for ITER as 1415mm x 1095mm x 450mm. And the ITER blanket is sure to stop almost all the 14 MeV neutrons.

MSimon
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Post by MSimon »

Axil wrote:The General Fusion approach uses lead to form the compression wave that produces D-D or D-T fusion. The neutron energy that is produced exceeds 14MeV. These high energy neutrons will penetrate many tens of meters of lead (14 * 4 = 56 meters). General Fusion does not provide a blanket to absorb those neutrons. This lack of a blanket will make their fusion reactor very dangerous. The steel of the reactor will radiate heavy gamma rays due to neutron activation and the acoustic generators will be unapproachable for maintenance.

This is a major design oversight. General Fusion will be required to build their reactor conformant with the need to add a blanket to slow and absorb fast neutrons.
It is a lead/lithium mixture.
Engineering is the art of making what you want from what you can get at a profit.

Axil
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Post by Axil »

Sorry, it is not a bad as I thought. I was mislead by the simulation where General fusion used pure lead as the reactor coolant. That simualtion is misleading. Yes, they actually use Lithium-Lead (17Li-83Pb). The Lithium Lead provides 17% lithium as the moderator to slow the fast neutrons down. Most of that lithium (92.5%) is Lithium 7. That is still not enough to absorb all the fusion neutrons. The neutron absorbtion cross section of lithium 7 is too limited.

ITER uses flibe; a mixture of beryllium fluoride and lithium fluoride in their blanket. Lithium, fluorine, and especially beryllium slow and absorb many neutrons, but it is the boron in the carbon that stop all the fusion neutrons.

General Fusion cannot use all these light, low density materials in their coolant because that thin coolant cannot carry the energy required to form the compression wave. A blanket that carries these light elements will mitigate these shortcomings.

choff
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Post by choff »

I don't imagine molten lead-lithium can be make to behave like transmission fluid.
CHoff

Axil
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Post by Axil »

http://www-ferp.ucsd.edu/LIB/PROPS/PANOS/lipb.html

Here above are some Lithium-Lead GENERAL PROPERTIES that will make the general fusion inc. simulations more realistic ( if they read this thread). One area of concern is the drop in coolant density as its temperature rises. To get 33% efficiency, a temperature of around 600C is needed. That may thin out the density of the lead coolant to preclude sufficient wave compression power. From eyeballing the chart, assuming linearity, at 650 C, the density is about 8800.

MSimon
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Post by MSimon »

One point to keep in mind is that the guys used to design ink jet print heads. A similar mechanical problem.
Engineering is the art of making what you want from what you can get at a profit.

Axil
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Post by Axil »

MSimon wrote:One point to keep in mind is that the guys used to design ink jet print heads. A similar mechanical problem.
I wish them the best of luck. Tom Edison changed his world by trial and error, you never can tell. The important concept is to verify the concept of compressing D-T to fusion using a shock wave. All else can be fixed.

Art Carlson
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Post by Art Carlson »

Axil wrote:Sorry, it is not a bad as I thought. I was mislead by the simulation where General fusion used pure lead as the reactor coolant. That simualtion is misleading. Yes, they actually use Lithium-Lead (17Li-83Pb). The Lithium Lead provides 17% lithium as the moderator to slow the fast neutrons down. Most of that lithium (92.5%) is Lithium 7. That is still not enough to absorb all the fusion neutrons. The neutron absorbtion cross section of lithium 7 is too limited.
The main reason to use lithium in the blanket of a D-T reactor is not to slow or absorb neutrons but to breed tritium. The main reaction is
  • n + 6Li -> T + alpha
This is dandy and even gives you a bit of extra energy. The problem is that it gives you exactly one triton for every neutron. Since some of the neutrons will get lost in various ways, this is a losing proposition. Fortunately there is also the reaction
  • n + 7Li -> T + alpha + n
This gives you a triton but also gives you your neutron back. The trouble is that this reaction is endothermic, so it won't go on forever. But it can give you enough extra neutrons to make up for the ones you lose elsewhere. Adding lead to the mixture helps, too, because it is relatively common for one neutron to knock another neutron out of a lead nucleus.

choff
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Post by choff »

I started getting the idea that the Popular Science writer screwed up his explanation of General Fusion's idea, so I did a search on their patent and on LINUS. He didn't, but maybe it would make more sense using the imploding lead lithium as a means to capture reaction energy as opposed to driving the reaction.
CHoff

GreenGirl
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Post by GreenGirl »

I love that we are so advanced in technology but I just don't understand why we don't take this grant money and put it towards something that could be used to improve everyday life. For example, the work on these micro turbines could be used to conserve fossil fuels.

krenshala
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Post by krenshala »

GreenGirl wrote:I love that we are so advanced in technology but I just don't understand why we don't take this grant money and put it towards something that could be used to improve everyday life. For example, the work on these micro turbines could be used to conserve fossil fuels.
Isn't the entire point of these grants to allow people the funding to develop things that can improve everyday life? I would definitely call the successful development of a new power source an improvement ... and doing that requires funding from somewhere.

Roger
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Post by Roger »

GreenGirl, Polywell would make liquid fuels quaint. DO you mean the Polywell monies?
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

MSimon
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Post by MSimon »

Roger wrote:GreenGirl, Polywell would make liquid fuels quaint. DO you mean the Polywell monies?
At our current level of technology (say the next 100 years) liquid fuels will not be quaint. They may be displaced in autos and ships in the next 50 to 75 years (it will be difficult), but displacing them in aircraft is going to be really tough.

What is more likely is that a Polywell will make the mfg. of liquid fuels on a par with drilling for them.
Engineering is the art of making what you want from what you can get at a profit.

katana0182
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Post by katana0182 »

MSimon wrote:
Roger wrote:GreenGirl, Polywell would make liquid fuels quaint. DO you mean the Polywell monies?
At our current level of technology (say the next 100 years) liquid fuels will not be quaint. They may be displaced in autos and ships in the next 50 to 75 years (it will be difficult), but displacing them in aircraft is going to be really tough.

What is more likely is that a Polywell will make the mfg. of liquid fuels on a par with drilling for them.
Aircraft, well, you never know, possibly good ol' Mr. Fission might be able to help, if it can be made safe.

A jet engine just requires heat, I think - it doesn't care where it gets its heat from, so long as it's compact - could be a liquid salt - like thorium fluoride... But that'll require some hearts to change as well as minds.

EMSmith
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Post by EMSmith »

In my opinion, these guys don't need 200 steam pistons, they need 200 machine guns.
According to the linked article, they're looking to produce 2 GPa shockwave pressure at 200 places all at exactly the same time, 2 times a second.
Machine guns, with electronic ignition. Use cast explosive pellets to generate their 2 GPa shock wave. Those levels of pressure are not anything difficult to generate; 20 GPa is common in explosive hydroforming, for example.
The machine guns wouldn't have to be so precise, as long as they deliver the new charge with time to spare before the next shot. 120 RPM is pretty lazy, from that perspective.
Only the ignition electronics need be precise, but that is an already-solved problem; as someone mentioned on here before, implosion nuclear bombs trigger with that level of accuracy with very good reliability.

In any event, that's my kind of machine! Smoke and fire all over the place, 200 machine guns firing at 120 RPM continuously... this thing would thunder! :)

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