Talk-Polywell.org

Just out of curiosity, how large would the MaGrid have to be, assuming superconducting magnets, in order to fuse air without needing a vacuum? I'm thinking a giant tower of a machine like something Telsa would have built, or like the alien machine they build in the movie Contact.

About 30 miles across with a 100 Tesla field at the center of the donut.

i.e. not any time soon.

MSimon wrote:About 30 miles across with a 100 Tesla field at the center of the donut.

Basis?

My analysis on it: MSIMON being a SmaaartAarrse.



Basis: Thousands of posts read.

ladajo wrote:My analysis on it: MSIMON being a SmaaartAarrse.

:D

Basis: Thousands of posts read.

Give that man a seeegar.

The difficulty with fusing oxygen is that it is a high charge atom with low fusion yield.

Better? ;-)

Hokey dokey, pokey!

MSimon wrote:The difficulty with fusing oxygen is that it is a high charge atom with low fusion yield.

Better?

No no Simon, use air augmentation to boost the thrust and Isp even further. Treat the polywell engine exhaust as a preheater for the hydrogen, being fed into a ramjet, you're going to get a 3500 second Isp boost as well as additional thrust from the hydrogen/ atmospheric oxygen combustion augmenter. You should generate about another SSME of thrust that way.

IntLibber wrote:

MSimon wrote:The difficulty with fusing oxygen is that it is a high charge atom with low fusion yield.

Better? ;-)

No no Simon, use air augmentation to boost the thrust and Isp even further. Treat the polywell engine exhaust as a preheater for the hydrogen, being fed into a ramjet, you're going to get a 3500 second Isp boost as well as additional thrust from the hydrogen/ atmospheric oxygen combustion augmenter. You should generate about another SSME of thrust that way.

I thought the question was fusing air/oxygen.

MSimon wrote:The difficulty with fusing oxygen is that it is a high charge atom with low fusion yield.

Better?

Air? Mostly nitrogen.

If you start throwing the consituents of air around, the dominant reaction would be the DD from the water vapour.

Next up would be the p15N reactions that I like to discuss (as my 'pet' project when the opportunity arises).

There are research papers on the subject of DD reactions in lightning. There is evidence that you get a measurable neutron yield in this scenario, both practical and if you do the calc on likely yields.

chrismb wrote:If you start throwing the consituents of air around, the dominant reaction would be the DD from the water vapour.

Next up would be the p15N reactions that I like to discuss (as my 'pet' project when the opportunity arises).

There are research papers on the subject of DD reactions in lightning. There is evidence that you get a measurable neutron yield in this scenario, both practical and if you do the calc on likely yields.

Do you have any links on D-D lightning?

http://www.informnauka.ru/eng/2005/2005 ... 5_65_e.htm

You can do a few calcs yourself easily enough and you'll see you get some significant neutron rates if you assume all the deuterons in a lighning channel are energised to the full drive potential.


Fully saturated air at 40C = ~50g[H2O]/m3 = 1.7E24 molecules/m3
Assume H/D = 6400, D density = 2.5E14/cc
Assume cross section of 0.1barn at 300keV, two deuterons at 75keV so v=2.7E8cm/s
Reaction rate = 2.5E14.cm-3^2*0.1E-24.cm2*2.7E8.cm/s = 1.7E12reactions/s/cc

Assume cross section of 35millibarn at 20keV, two deuterons at 5keV so v=7E7cm/s
Reaction rate = 2.5E14.cm-3^2*0.035E-24.cm2*7E7.cm/s = 1.5E11reactions/s/cc

MSimon wrote:The difficulty with fusing oxygen is that it is a high charge atom with low fusion yield.

Better?

..almost as if this machine is fated to be operated in space

My two cents worth.

Fusing air in a Polywell is possible with a midsize machine- perhaps 30-50 meters in diameter (a pure guess).
Ignoring the trace deuterium present, the dominate reaction would be the P-N15 reaction, followed by the P-C12 (?). Fusing oxygen, nitrogen 14, etc. to heavier elements is not needed. Nitrogen in the dry atmosphere is ~ 30% nitrogen15. Protons would come from humidity (water vapor makes up ~ 5% of the atmosphere with high humidity levels). The only crossection for P-C12 I have seen suggests that the fusion rate would be ~ 1 % that of deuterium at several hundred KeV. P-N15 is presumably somewhat higher than this (both are reactions contained within the CNO fusion cycle that is dominate in large main sequence stars, and both are more rapid reactions than the rate limiting steps which I beleive involves one of the intermediate oxygen isotopes). The rapid B^4 r^3 scaling should limit the growth needed to reach usefull conditions.

As for running the reactor in air without a vacuum shell, the major problem would presumably be arcing. A Polywell in the few meters range has to limit the pressure outside the magrid to perhaps ~ 1/100,000 th of an atmosphere. A much larger machine may allow higher pressures (just as thicker wires can carry higher voltages without corona discharge) but I suspect the pressures would still need to be maintained at levels well below atmospheric.

Then there is the damping effects of all the contaminate gasses like oxygen and nitrogen14...

Bottom line: Once the Boron11 is used up, an advanced civilization could still fuel a larger Polywell (if it works at all) with componets isolated from the atmosphere (or oceans). As Bussard said, the Polywell could scale to burn any net positive energy fusion fuel. The Earths oceans already contain enough deterium fuel to power production, perhaps till the Sun becomes a Red Giant. At that stage if mankind persisted, they would be living on the moons of Jupiter, or further out. Plently of hydrogen/ deuterium aviable out there (and possibly boron in asteroids and moons). After a few hundred billion years, when the Sun is a cooling white dwarf, mankind might have to eventually find another star system to exploit for energy. The accelerating universe would eventually limit us to only the local group of galaxies. A dim and cold collection of a few trillion(?) stars and planets by then, but still lots of elemental resources.

Of course, even with extreamly small genetic drift, mankind would be far different and diverse, unless some artifical genetic standard is maintained. This assumes that mankind is the only game in town and that a central nearly(?) ominescent and omnipotentant athority polices the genetic pool.

Dan Tibbets


Dan Tibbets