D Tibbets wrote:
Thanks to a post by Dustin on the fusor.net site, this link provides more details and interesting information. Perhaps (if my perception of the neutral population in the Polywell being scant is correct) the relative lack of neutrals in the Polywell has a much more profound effect on efficiencies than has been appreciated.
Skipping to the summary; "Proton collimation experiments verify that the diffuse fast neutral population provides most of the observed fusion production, especially for the glow discharge modes (P > 100 mPa)....These results are inconsistent with the expectations from the multiple well model or any other model invoking a centralized source of reactivity."
....agreed!!...
Unless the neutrals are taken out of the equation as I sugested. While the neutrals contribute to the fusion rate, I'm contending that thier absence would allow the fast - fast collisons to dominate in a net benificial way. Or, the fast - neutral collisions (with the vast majority being nonfusing collisions) impeads the confluence and nonthermal maintanance of the ions. If the ions do have a tendancy to anneal in the perifery, the presence of significant neutrals would dillute or oppose this effect because of the random nature of the collisions throughout the entire volume of the Wiffleball.
D Tibbets wrote:
Thanks to a post by Dustin on the fusor.net site, this link provides more details and interesting information. Perhaps (if my perception of the neutral population in the Polywell being scant is correct) the relative lack of neutrals in the Polywell has a much more profound effect on efficiencies than has been appreciated.
Skipping to the summary; "Proton collimation experiments verify that the diffuse fast neutral population provides most of the observed fusion production, especially for the glow discharge modes (P > 100 mPa)....These results are inconsistent with the expectations from the multiple well model or any other model invoking a centralized source of reactivity."
....agreed!!...
Unless the neutrals are taken out of the equation as I sugested. While the neutrals contribute to the fusion rate, I'm contending that thier absence would allow the fast - fast collisons to dominate in a net benificial way. Or, the fast - neutral collisions (with the vast majority being nonfusing collisions) impeads the confluence and nonthermal maintanance of the ions. If the ions do have a tendancy to anneal in the perifery, the presence of significant neutrals would dillute or oppose this effect because of the random nature of the collisions throughout the entire volume of the Wiffleball.
Dan Tibbets
A hopefully ballpark comparison of the neutral population in a glow discharge fusor and a Polywell and the influence on Fast ion - fast ion collisions versus fast - neutral collisions.
In a hydrogen fueled fusor with a current of a few tens of milliamps there would be ~ 3-5 *10e17 charge carriers, half of which are ions, so round down to ~ 10e17 ions. If the pressure was 100 mPa the total number of particles (ions plus molecules) would be ~ 6*10e19 / 22.4 liters. In my convient fusor volume of ~ 4 liters this would work out to be ~ 10e19 neutrals, or ~ 100 neutrals per ion. Using Bussard's estimate of ~ 1000 ion to neutral ratio inside the magrid of the fusor that is a given requirement for net power fusion without external arcing (the external particle density would consist of evenly distributed neutrals plus escaped charged particles) results in a difference of ~ 100,000 in the ion to neutral proportions in the Polywell versus a glow discharge fusors like in the above reference.
If the 1/100 ratio of ions to neutrals results in a 10,000 fold preference for fast -neutral fusions over fast - fast fusions (ratio squared), then the ratios in the sucessfull Polywell would faver a fast - fast fusion preference to the order of ~ 1,000,000. So, if my math and assumptions are not way off, the fast - neutral fusion rate should be insignificant in the Polywell.
D Tibbets wrote:
Unless the neutrals are taken out of the equation
Wouldn't that be wonderful!
The thread was about fusors, though, and why they won't get to net-power. Fusors operate with a background gas - they're discharge devices.
D Tibbets wrote:
In a hydrogen fueled fusor with a current of a few tens of milliamps there would be ~ 3-5 *10e17 charge carriers, half of which are ions
I do wonder why I bother to write anything! 1/60th will be ions....
D Tibbets wrote:
If the 1/100 ratio of ions to neutrals results in a 10,000 fold preference for fast -neutral fusions over fast - fast fusions (ratio squared), then the ratios in the sucessfull Polywell would faver a fast - fast fusion preference to the order of ~ 1,000,000. So, if my math and assumptions are not way off, the fast - neutral fusion rate should be insignificant in the Polywell.
The thread was about fusors, though, and why they won't get to net-power. Fusors operate with a background gas - they're discharge devices.
D Tibbets wrote:
Unless the neutrals are taken out of the equation
Wouldn't that be wonderful!
The thread was about fusors, though, and why they won't get to net-power. Fusors operate with a background gas - they're discharge devices.
D Tibbets wrote:
In a hydrogen fueled fusor with a current of a few tens of milliamps there would be ~ 3-5 *10e17 charge carriers, half of which are ions
I do wonder why I bother to write anything! 1/60th will be ions....
D Tibbets wrote:
If the 1/100 ratio of ions to neutrals results in a 10,000 fold preference for fast -neutral fusions over fast - fast fusions (ratio squared), then the ratios in the sucessfull Polywell would faver a fast - fast fusion preference to the order of ~ 1,000,000. So, if my math and assumptions are not way off, the fast - neutral fusion rate should be insignificant in the Polywell.
The thread was about fusors, though, and why they won't get to net-power. Fusors operate with a background gas - they're discharge devices.
1/60th or 1/100th, close enough for my ballpark estimates (accurate numbers would depend on the actual measured current, 10 mA might match my numbers while 20 mA may be closer to yours). As you say, a glow discharge machine is limited by the neutrals, but as you have also said, using ion injection with better vacuum changes the story. I think I have read that if scaled large enough, a Hirsch type of fusor might reach breakeven, at least if you conveniently ignore bremsstrahlung losses. Why this was not pursued back in the 1970's before Rider highlighted the bremsstrahlung problem is unknown. Perhaps they realized the sizes needed would be completely impractical. This was also before the POPS concept developed by Nebel, et el which might not reach breakeven but might make for a powerful compact neutron source useful for fusion fission hybrids.
D Tibbets wrote: Unless the neutrals are taken out of the equation
Wouldn't that be wonderful!
The thread was about fusors, though, and why they won't get to net-power. Fusors operate with a background gas - they're discharge devices.
Actually, the thread was about how a magnetically protected grid might change a loser-fuser into a Gainer.
If the negatively charged MaGrid would allow concentration of ions in the core rather than flitting around the machine, and if the neutrals were kept down in population, this would lead to a fast-fast machine, not a fast-neutral machine. If you MUST call it something other than a fusor to allow thought outside the fuser=fast-neutral, then do so. But could such a machine be made to work?