I think Art's right that you have to build it. There are limits to what modelling can tell us, as the tokamak community has found out.
So we probably need $200M to find out if Polywell can work, and $20B to see if the ITER path can lead anywhere useful. Hopefully, we'll see both funded.
That makes an effective length of about 2*12*(2pi*R/4), call it 15 m. Let's guess B = 1 T, so rho_e at 100 keV is around 1 mm. Multiply that times 8 (the fourth root of the deuteron/electron mass ratio) for the hybrid gyroradius, assuming standard theory holds. Makes 8 mm cusp width.
Hrm. I don't think Bussard calculated it that way. Are you assuming quasineutrality here? The ion pressure should be low.
Last edited by TallDave on Wed Feb 04, 2009 3:21 am, edited 2 times in total.
Something I am curious about concerning fuel sources (considering that I am a total layman here, go easy on me ). The way I understand it, any element that becomes ionized once introduced into the system could be used as fuel because it would be attracted to the electron well in the center, and the driving force behind selecting different fuels was to control high energy neutron output.
But if the neutron radiation can be accounted for and protected against, why couldnt the polywell literally run as a 'flex-fuel' fusor off of anything you toss into it?
I'm another layman, so take what I say and disbelieve it thoroughly.
But look at Fusion Cross-Sections (scroll down to the paragraph that starts with "The reaction cross section").
Some materials will fuse very easily, and others hardly at all. You can get more fusions by cranking up the temperature (also the electrical field, since it will drive the particles together faster). But there are limits to how high you can go, and since we're so new at this we can't go very high.
Some potential reactions produce a LOT of energy for only a little input. (D-D, D-T, p-B11). Other reactions will fuse (theoretically), but they won't even release the energy put into them (e.g. fusing a Lanthanide or Actinide series element).
That's just a start to this discussion, but I think they're focusing on the D-D (deuterium), D-T (tritium) and p-B11 (Boron "aneutronic") fusion because it produces LOTS of energy...
That makes an effective length of about 2*12*(2pi*R/4), call it 15 m. Let's guess B = 1 T, so rho_e at 100 keV is around 1 mm. Multiply that times 8 (the fourth root of the deuteron/electron mass ratio) for the hybrid gyroradius, assuming standard theory holds. Makes 8 mm cusp width.
Hrm. I don't think Bussard calculated it that way. Are you assuming quasineutrality here? The ion pressure should be low.
Of course Bussard calculated it differently. He assumed the cusp width was equal to the electron gyroradius, although there was published experimental and theoretical evidence that the hybrid radius (the factor of 8 here) was the lower bound. Either he didn't do his homework or he didn't cite and discuss previous work. Either one of these is a major sin in serious science.
<sigh> Of course I assumed quasineutrality. I always assume quasineutrality. More precisely, I don't assume it, I estimate the parameters and conclude that the plasma must be quasineutral. Check the archives, I don't feel like presenting the calculations yet again.
What's the power loss through the cusp, again assuming standard theory (or worst case, depending on your point of view)? An area of 0,1 m^2. An energy density of (1 T)^2/(2mu_0) ~ 4e5 J/m^3. A sound speed of about 2e6 m/s. Adds up to 100 GW. We're gonna need a bigger boat!
Using 1/8th the width, and ½ the length, and assuming 99%+ return efficiency on the electrons, we are down to ~the 40MW that Dr. B wrote of.
Why stop there? Let's just say the plasma pressure is 1/10 the magnetic pressure (even though they are in equilibrium) and the gamma factor in the speed of sound in 0.01 (even though the "standard theory" says it can't be less than 1). Then we are down to 400 kW. Wow, this thing just keeps looking better and better!
StevePoling wrote:Can anyone articulate an experiment that would falsify either proposition? I mean something cheaper than building a fully-operational Wiffleball-N?
I spent some more time pondering this. I was thinking in the direction of leaving out the cusp itself and just investigating a pencil of plasma propagating along a field through hoops of various potential. Then I realized this is pointless because whiffle-ball theory is not falsifiable.
I mean, suppose I set up an experiment involving cusp physics and electric fields and I showed that it all worked as I expected. What would the polywell proselytes say? That the real polywell has (unspecified) non-Maxwellian effects that my setup didn't take into account. That is basically the last answer I got from Rick Nebel. Of course I can't refute that because nobody has ever said what those effects might be in detail. Maybe if I worked real hard for a year or so (Are there any volunteers to pay my salary?), I could prove a fairly general theorem that would rule out a large class of options. (My shining example for this type of calculation is Todd Rider.)
Basically, there is no whiffle ball theory, only some handwaving with manifest inconsistencies. On the experimental side, there is no published, robust evidence that anything unusual is happening at all. What are we doing here?
Art Carlson wrote:
On the experimental side, there is no published, robust evidence that anything unusual is happening at all. What are we doing here?
Not enough, from what I can see. Here is how I see it. If this whiffle ball thing will not work, then we need to stop spending money on fusion and start spending money on fast-breeders and conventional fission plants.
Crude oil is too valuable to burn. Many economists will jump salty at me for saying such a thing, but it is true. Economic theory is NOT universally applicable. Free markets will NOT answer every need, as much as I hate saying that. Look around your house. It and nearly everything in it was made from crude or has something made from crude in it or on it. Replacing those products after all the crude is gone will be a non-trivial effort. Coal, in my not-so-humble opinion is too nasty to burn and "clean" coal will likely prove to be entirely too expensive to burn.
That leaves us with fusion or fission. We will do one or the other and we need to start doing some of both ten years ago. We have been piddling around for much too long now.
StevePoling wrote:Can anyone articulate an experiment that would falsify either proposition? I mean something cheaper than building a fully-operational Wiffleball-N?
I spent some more time pondering this. I was thinking in the direction of leaving out the cusp itself and just investigating a pencil of plasma propagating along a field through hoops of various potential. Then I realized this is pointless because whiffle-ball theory is not falsifiable.
I mean, suppose I set up an experiment involving cusp physics and electric fields and I showed that it all worked as I expected. What would the polywell proselytes say? That the real polywell has (unspecified) non-Maxwellian effects that my setup didn't take into account. That is basically the last answer I got from Rick Nebel. Of course I can't refute that because nobody has ever said what those effects might be in detail. Maybe if I worked real hard for a year or so (Are there any volunteers to pay my salary?), I could prove a fairly general theorem that would rule out a large class of options. (My shining example for this type of calculation is Todd Rider.)
Basically, there is no whiffle ball theory, only some handwaving with manifest inconsistencies. On the experimental side, there is no published, robust evidence that anything unusual is happening at all. What are we doing here?
But it is falsifiable at least ultimately. Either you get more power out than you put in or you don't.
For $10 million we build the SC job and that should tell us if a power producer is possible. It should also be possible to measure the wiffle-ball. Lasers. Microwaves. Field probes. Whatever.
I must say though that I'm starting to feel like a tokamak guy: "there are problems that can only be worked out at the next larger level". It must be a plasma physics disease.
Engineering is the art of making what you want from what you can get at a profit.
I think going up in funding from 1 million to 200 million based on three neutrons on a neutron counter is far too much. I'm sure there is plenty of falsifiable things that can occur at the 10 million dollar level.
Whether there's anything at all in Polywell physics or not, the one thing I've learnt from this is just how inefficient defense projects shrouded in secrecy are. Just listening to Dr. Bussards google talk you can see this, he built vast white elephants that cost 10's of millions of pounds over 10's of years when a proper peer reviewed process would probably have spotted their numerous flaws on paper aswell as potential improvements before they were even built.
He spent too much money on building large machines that were big enough to achieve net fusion power if they satisfied his hand-wavy criteria and not enough money thinking of ways of properly testing his hand-wavy criteria on a smaller level.
After looking at the state of Polywell research after 20 years in the hands of the U.S. military I'm starting to doubt these conspiracy theorist who say the technology the U.S. military possess "is beyond anything you can ever imagine"
Perhaps engineering can works when it comes to black projects but fundamental science doesn't.
Here is what I think is "falsifiable" in the eyes of the Navy.
The plant must be able to start from power generated by a V-12 Caterpillar diesel. Once started, it must supply enough power to sustain itself plus the power needed to run the Navy's latest version of an AEGIS cruiser. Oh, and it will have to do so with no down time for at least a year at a time between overhauls.
The demands for an onshore civilian system would not be quite so stringent, but it would then be supplying power for at least a small town, say a population of 25,000--something around 30MW.
If there are no fusion plants capable of this, we go back to coal and fission or, maybe, methane clathrates.
Billy Catringer wrote:If there are no fusion plants capable of this, we go back to coal and fission or, maybe, methane clathrates.
Those are real options, but they have a certain ugliness about them (either radioactive waste or greenhouse gases). Why not solar power (thermal cycle, built in the desert with the electricity piped to civilization over HVDC lines)? Or off-shore wind? (I haven't given up on hot-dry-rock geothermal, either, although it's pretty iffy.)
Billy Catringer wrote:If there are no fusion plants capable of this, we go back to coal and fission or, maybe, methane clathrates.
Those are real options, but they have a certain ugliness about them (either radioactive waste or greenhouse gases). Why not solar power (thermal cycle, built in the desert with the electricity piped to civilization over HVDC lines)? Or off-shore wind? (I haven't given up on hot-dry-rock geothermal, either, although it's pretty iffy.)
You know our biggest research hole is not fusion. It is energy storage.
We will soon know how to make solar and wind cheap enough. We have no clue on how to make electrical energy storage cheap enough.
Engineering is the art of making what you want from what you can get at a profit.
Billy Catringer wrote:If there are no fusion plants capable of this, we go back to coal and fission or, maybe, methane clathrates.
Those are real options, but they have a certain ugliness about them (either radioactive waste or greenhouse gases). Why not solar power (thermal cycle, built in the desert with the electricity piped to civilization over HVDC lines)? Or off-shore wind? (I haven't given up on hot-dry-rock geothermal, either, although it's pretty iffy.)
You know our biggest research hole is not fusion. It is energy storage.
We will soon know how to make solar and wind cheap enough. We have no clue on how to make electrical energy storage cheap enough.
That's one of the reasons I like solar thermal electricity. It's very hard to store electricity, but relatively straightforward and cheap to store heat. For a modest additional investment, you can add thermal storage for a few hours or even a few days to your desert power plant. And you can factor in the fact that the sun is pretty reliable in the desert, in an emergency you can replace the solar heat with fossil fuels, and long-range electricity lines help smooth things out.
Then, of course, there's pumped hydro. Even compressed gas looks like an option, especially where the energy source is mechanical, like wind. (May be tough to do it off-shore though.)
I'd say the biggest hole is production of transportable energy, i.e. fuel. I don't think much of hydrogen, and it'll be tough to get enough biofuels.
Art Carlson wrote:
Those are real options, but they have a certain ugliness about them (either radioactive waste or greenhouse gases). Why not solar power (thermal cycle, built in the desert with the electricity piped to civilization over HVDC lines)? Or off-shore wind? (I haven't given up on hot-dry-rock geothermal, either, although it's pretty iffy.)
You know our biggest research hole is not fusion. It is energy storage.
We will soon know how to make solar and wind cheap enough. We have no clue on how to make electrical energy storage cheap enough.
That's one of the reasons I like solar thermal electricity. It's very hard to store electricity, but relatively straightforward and cheap to store heat. For a modest additional investment, you can add thermal storage for a few hours or even a few days to your desert power plant. And you can factor in the fact that the sun is pretty reliable in the desert, in an emergency you can replace the solar heat with fossil fuels, and long-range electricity lines help smooth things out.
Then, of course, there's pumped hydro. Even compressed gas looks like an option, especially where the energy source is mechanical, like wind. (May be tough to do it off-shore though.)
I'd say the biggest hole is production of transportable energy, i.e. fuel. I don't think much of hydrogen, and it'll be tough to get enough biofuels.
Hydrogen is not bad if you connect it up with carbon.
Engineering is the art of making what you want from what you can get at a profit.
What's the power loss through the cusp, again assuming standard theory (or worst case, depending on your point of view)? An area of 0,1 m^2. An energy density of (1 T)^2/(2mu_0) ~ 4e5 J/m^3. A sound speed of about 2e6 m/s. Adds up to 100 GW. We're gonna need a bigger boat!
Using 1/8th the width, and ½ the length, and assuming 99%+ return efficiency on the electrons, we are down to ~the 40MW that Dr. B wrote of.
Why stop there? Let's just say the plasma pressure is 1/10 the magnetic pressure (even though they are in equilibrium) and the gamma factor in the speed of sound in 0.01 (even though the "standard theory" says it can't be less than 1). Then we are down to 400 kW. Wow, this thing just keeps looking better and better!
Please Art, I am trying to get to a real understanding here. My factors are not being pulled out of the aether. I explained my disagreement with your numbers and assumed only that a MaGrid was a bit better than a plain grid at returning electrons. I did not try to assume impossibilities. I am just concerned that your "standard theory" is standard magnetic confinement theory... and that is NOT what we have here!
). The way I understand it, any element that becomes ionized once introduced into the system could be used as fuel because it would be attracted to the electron well in the center, and the driving force behind selecting different fuels was to control high energy neutron output.