Lawrenceville plasma physics June update

[GIThruster]

When I last spoke with Eric Lerner on this subject, he was dismayed that so much energy is carried away in X-Rays. They in fact had not originally planned to capture/convert them but their patented onion skin converter was designed just for this. The converter has not been built. If you look on their web site, you'll see that this is not planned until they have reason to demonstrate Q>1, which is not for some time yet. I don't think it is part of the plan for this phase of the work.

BTW, IIRC, the electrodes are beryllium specifically because it is transparent to x-Rays. IIRC, that's worth checking. . .

[chrismb]

.. if it was possible to recover x-ray energy, then, surely, all of a sudden you've just proved thermal fusion is viable because the problem with that is loss through brems in the x-ray region?

[GIThruster]

I think it's more complex than this. It's not just whether you recover the X-Rays. It's what energy is carried away from the reaction that does not then contribute to further reaction. Once an X-Ray, always an X-Ray.

Still, knowing what they do about brem production, they expect to get at least Q2 from B11. not from this phase of the work, but that is the goal, IIRC.

You can search and find the general design of their onion skin converter. The patent was already field, if not granted. This is all on their website as well as their fan site.

[chrismb]

You can search and find the general design of their onion skin converter. The patent was already field, if not granted. This is all on their website as well as their fan site.

I can search for it, you're right. I can also tell you that whatever I were to find, it would be all too speculative for my taste, until a prototype is built and working. For now, it is just a nice idea and I don't think it has reached the status of 'objectively debatable'.

[GIThruster]

Well I'm all ears if you want to explain what "objectively debatable" means.

If you have an interest and want to chase the patent, here's a lead:

http://focusfusion.org/index.php/site/a ... plication/

There are of course many methods for converting X-Rays to electricity. Some are heat cycles, some are photovoltaic, others are the later but use advanced meta-materials.

The question is not whether x-rays can be converted for use. The question is whether this can be done efficiently and economically enough to make them of use. Personally, I think Lerner is correct to chase one impossible goal at a time. In the meantime, it's noteworthy he has the confidence enough in his conversion method to file for patent. If it works, it will be just as useful surrounding a poly.

[D Tibbets]

.. if it was possible to recover x-ray energy, then, surely, all of a sudden you've just proved thermal fusion is viable because the problem with that is loss through brems in the x-ray region?

I'm not sure what your saying. Thermal systems like a Tokamak could burn P-B11 if you could get the average temperature high enough. In thermal systems, to get efficient P-B11 fusion, the high thermal tail would produce more than it's fair share of bremsstrulung, eating into any fusion gain. If the bremsstrulung exceeds the fusion output, which it apparently does in the P-B11 temperature range for thermalized systems, and you can recover enough of what otherwise is waste energy- through a thermal steam cycle (25-30% recovery) or a direct conversion (optimistically 80-90%), then yes you might still squeeze out a net positive Q.
How much bremsstrulung x-ray recovery would you need in a super Tokamak* that could heat a thermalized plasma to adequate temperatures?
Is 80% recovery enough, 99.9% recovery...?

* I understand that it is extremely difficult to heat a Tokamak thermalized plasma to temperatures adequate for D-T fusion. P-B11 would require an average temperature perhaps 10-20(?) times as high.

PS: I'm not sure whether the DPF has a thermalized plasma.
If so, apparently ~ 80% x-ray conversion is sufficient to provide positive gain with P-B11, once the claimed quantum effects on x-ray suppression is included. A Tokamak would not have this claimed advantage, so would need higher X-ray energy recovery. What is the magnitude of this effect?


Dan Tibbets

[chrismb]

If you have an interest and want to chase the patent, here's a lead:

http://focusfusion.org/index.php/site/a ... plication/

There are of course many methods for converting X-Rays to electricity. Some are heat cycles, some are photovoltaic, others are the later but use advanced meta-materials.

You use the present tense. Please give me some references so that I may see these wonder devices.

Incidentally, the link contains old news. That patent application was granted - and it contains the briefest of descriptions on this, alluding to a sandwich of thin films that generate power by photovoltaic effect. Problem is, how thick will that sandwich have to be? I rather think you will find it is necessary for it to be on the order of several tens of miles thick. This is not a practicable solution.

[93143]

You can stop these X-rays with a few inches of lead. Below 300-400 keV, almost all of the stopping power is derived from the photoelectric effect.

The sandwich design will have to be bigger, of course, but "miles" is silly.

[GIThruster]

Edited for better intent. Not doing your research for you, Chris. If you want to hire me, I'm at $250/hour.

I'm sure you think you can do a better job, yes?

[chrismb]

You can stop these X-rays with a few inches of lead. Below 300-400 keV, almost all of the stopping power is derived from the photoelectric effect.

The sandwich design will have to be bigger, of course, but "miles" is silly.

Really? Well, by how much? Looks to me like the design calls for foils of material, spaced by cms. So let's say the foils are 10um and the gaps are 1cm, so then we need a sandwich 1000x your few inches. Let's call it 100 metres. The we have to mutlipy that up by the reduction in stopping capacity between the proposed beryllium and the lead which you are basing your few inches on. I will initially presume that is a factor of Z, but will be happy for you to make your own comments on mfp of xrays in beryllum versus lead. Let's say it is 207/9=~20. So based only on the notion of density difference (which I presume is an underestimate, as I would more expect stopping power to be a Z^2 term or something, but don't really know) then that'd make a lerner-x-ray sandwich of over a mile.

That'd be an impressive sight - a sphere two miles in diameter to collect x-rays from a fusion reactor at the centre.- 10 out of 10 for sytle, minus several million for practicality, eh?

[chrismb]

Edited for better intent. Not doing your research for you, Chris. If you want to hire me, I'm at $250/hour.

I beg you pardon?!?

This is a public forum in which [one might've thought] technical matters were discussed freely.

You have said that x-ray energy recovery devices exist, I have said that this is bolloks, and now it's your turn to contribute the information that proves I am a dunce and a know-nothing.

I cannot go and find something that doesn't exist. It is impossible for me to prove that something doesn't exist so it cannot be my obligation to prove this. You have made the claim that something exists, so it is your obligation to show that it is so, because it is easy to show something exists, if it does, simply by showing it.

I declare you are a faker and a schmoozer if you choose to state x-ray recovery machines currently exist. Now defend yourself, and show these things do exist.

[Skipjack]

Not sure if I understood you right Chris, but at a 1000 layers and a centimeter per Layer, you would get 10 meters, not 100 meters.

[kcdodd]

Impractical either way. Easier just to let them hit the wall and extract at 30% eff. by steam turbine.

Also I still do not think anything has been shown to say they have reached Q=0.5. The amount of energy in the plasma is irrelevant. The fusion energy is negligible from the numbers they have given.

[Skipjack]

NBF hast another LPP update on there.
http://nextbigfuture.com/2010/06/rewrit ... s-and.html

[D Tibbets]

You can stop these X-rays with a few inches of lead. Below 300-400 keV, almost all of the stopping power is derived from the photoelectric effect.

The sandwich design will have to be bigger, of course, but "miles" is silly.

Really? Well, by how much? Looks to me like the design calls for foils of material, spaced by cms. So let's say the foils are 10um and the gaps are 1cm, so then we need a sandwich 1000x your few inches. Let's call it 100 metres. The we have to mutlipy that up by the reduction in stopping capacity between the proposed beryllium and the lead which you are basing your few inches on. I will initially presume that is a factor of Z, but will be happy for you to make your own comments on mfp of xrays in beryllum versus lead. Let's say it is 207/9=~20. So based only on the notion of density difference (which I presume is an underestimate, as I would more expect stopping power to be a Z^2 term or something, but don't really know) then that'd make a lerner-x-ray sandwich of over a mile.

That'd be an impressive sight - a sphere two miles in diameter to collect x-rays from a fusion reactor at the centre.- 10 out of 10 for sytle, minus several million for practicality, eh?

I was casually wondering how thick each layer/ lead foil was. Hopefully the intervening non lead layers where the photovotaic energy is transferred from each lead foil need not be very thick. Even if it is only 0.1 cm, the total thickness will still be 10 M(?). One mm layer thickness would be even more more manageable.

The beryllium is proposed for the central anode only (how about the cathodes?) because it is so transparent to X-Rays, and therefor wont be heated as much. This is apparently the dominate factor that determines the anode lifetime. I guess lithium might be better for X- ray transparency, but the melting point is also much lower.

Dan Tibbets