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Posted: Tue May 19, 2009 6:01 pm
by gblaze42
rnebel wrote:Nothing is a slam dunk. If the transport doesn't work out, then none of the systems will work. Right now, the transport looks fine. The question is whether or not it will scale.


Didn't know that. Now I'm really curious to see if this will work.

Posted: Tue May 19, 2009 6:14 pm
by Barry Kirk
I've been following Polywell on and off for a couple of years now, but I missed the definition of transport.

What is the transport issue?

Posted: Tue May 19, 2009 6:28 pm
by rnebel
Barry:

The transport issue is how fast energy leaves the system. You need to substantially more energy out in fusion than you inject into the machine. Transport losses determine how much energy you need to inject.

Posted: Tue May 19, 2009 6:33 pm
by Barry Kirk
Thanks...

So, it is effectively how fast you can get the energy out, ( maybe in the form of high energy alphas? ), of the machine compared to the rate that energy is injected into it?

Posted: Tue May 19, 2009 6:48 pm
by 93143
Sort of. We can assume that if there's energy produced by fusion, we can get it. The question is, how much energy do we have to inject to make up for losses (transport=leakage of high-energy electrons and fuel ions through the confinement, leading to loss of their energy)? If it's significantly less than the fusion power, we're good (at least for simple fuels where stuff like bremsstrahlung isn't an issue).

Posted: Tue May 19, 2009 6:49 pm
by Barry Kirk
Aha... Did some searching on the web.... Should have done my homework before the last post...

I thing you were referring to the electrons being transported out of the machine and effectively lost?

Posted: Tue May 19, 2009 6:51 pm
by Barry Kirk
I seem to remember that Polywells can recirculate the electrons and possibly the ions so that most of the electrons that escape the cusps end up back inside the well with minimal energy loses...

Posted: Tue May 19, 2009 7:13 pm
by gblaze42
93143 wrote:Sort of. We can assume that if there's energy produced by fusion, we can get it. The question is, how much energy do we have to inject to make up for losses (transport=leakage of high-energy electrons and fuel ions through the confinement, leading to loss of their energy)? If it's significantly less than the fusion power, we're good (at least for simple fuels where stuff like bremsstrahlung isn't an issue).


Bremsstrahlung would be an issue when the plasma density goes up when trying to scale, no matter the how simple the fuels, this is one of the hurdles in Tokamak fusion reactors.

Dr. Nebels says the transport , at the moment, seems to be working, it will be interesting to see if it scales.

Posted: Tue May 19, 2009 8:31 pm
by Art Carlson
gblaze42 wrote:
93143 wrote:Sort of. We can assume that if there's energy produced by fusion, we can get it. The question is, how much energy do we have to inject to make up for losses (transport=leakage of high-energy electrons and fuel ions through the confinement, leading to loss of their energy)? If it's significantly less than the fusion power, we're good (at least for simple fuels where stuff like bremsstrahlung isn't an issue).


Bremsstrahlung would be an issue when the plasma density goes up when trying to scale, no matter the how simple the fuels, this is one of the hurdles in Tokamak fusion reactors.

I would say "easy" rather than "simple", meaning a relatively large fusion cross section.

The bremsstrahlung issue is independent of density, which is one reason the objections to p-B11 are so robust. Both the fusion power and the bremsstrahlung power scale with n^2.

Posted: Tue May 19, 2009 8:36 pm
by Art Carlson
rnebel wrote:I think we have a real shot at p-11B. I think it is possible to beat the Bremstrahlung issue.

That's a mighty terse statement. It may be that you have given your reasoning before, but I have forgotten it.
  • What do you anticipate for the ratio of P_brems to P_fusion?
  • Do you expect to get there by running with a low value of <E_e>/<E_i> or by tailoring the electron energy distribution?
I'm afraid whatever you answer there will be follow up questions.

Posted: Tue May 19, 2009 9:50 pm
by rnebel
The present projected Q values for p-11B vary from about 1.7 to about 12, depending on how the physics breaks. The details of how you do that are surprisingly subtle and coupled, and I'm not going to go into that in this forum. I view this as an "optimistic problem". There are a lot more serious issues that need to be dealt with than this one.

Posted: Wed May 20, 2009 2:01 am
by gblaze42
Art Carlson wrote:The bremsstrahlung issue is independent of density, which is one reason the objections to p-B11 are so robust. Both the fusion power and the bremsstrahlung power scale with n^2.


It is? I would think the probability for electrons to have a change in momentum goes up as the density of plasma goes up, as the likelihood that an electron would encounter a proton/nucleus increases. I'm curious, not being a plasma physicist.

Posted: Wed May 20, 2009 2:32 am
by 93143
Art Carlson wrote:I would say "easy" rather than "simple", meaning a relatively large fusion cross section.


That's what I meant. "Simple" as in "not difficult". "Easy" would have been better.

gblaze42 wrote:I would think the probability for electrons to have a change in momentum goes up as the density of plasma goes up


It does. So does the probability of fusion events. Net result is a wash.

Posted: Wed May 20, 2009 2:42 am
by KitemanSA
93143 wrote:
gblaze42 wrote:I would think the probability for electrons to have a change in momentum goes up as the density of plasma goes up
It does. So does the probability of fusion events. Net result is a wash.
Except that (as I understand it... minimally) the fusion rate is related to the a density function of BOTH species, p and B11, but the Brem is related most significantly to the density of B11. You can, in theory, increase fusion and decrease Brem by increasing the ratio of p to B11 and playing with the total pressure.

Posted: Wed May 20, 2009 3:16 am
by 93143
Of course. But the fuel mixing ratio is a separate parameter from the overall plasma density. Changing the density, without altering other parameters, doesn't get you anywhere. That's all.