Vacuum for free..

[Steven Sesselmann]

I had a thought today, which probably has been thought of before.

Fusion in space would be pretty easy, as it could be done without having to generate a vacuum. ie. No fusion chamber required, just two grids, anode and kathode, a few deuterium atoms and a power supply... Wahlah!

One could then utilize the energy released in various ways:

a)
By sheilding one side of the fusor neutrons and protons would be absorbed in the shield, giving the fusor a tiny directional thrust.

b)
By passing the fast protons past a coil of some description converting the kinetic energy directly into electricity.

Steven

[Richard Hull]

You would still need a sealed chamber much like we have on earth to contain the deuterium atmosphere inside the fusor. you would not need a vacuum pump, but would need a leak valve from the chamber to obtain flowing D2. Being in space you would solve only one problem. .... The $300.00 pump. The cost of being in space with its new associated difficulties would be in the 100 million dollar range.

Richard Hull

[UG!]

you would still need a chamber to keep the gas IN, or it would be of and away beffore it ever got ionised. i suppose you could use ion guns, but if your going to build an ion guns, you might as well use them for thrust (as is being done).

it would be handy to live on a space station and have a 10^-14 vacuum available on tap though

Oliver

[DaveC]

But the present "fusors" actually operate on a plasma. This is relatively modest vacuum level...a few microns, more or less.

You need little more than a good roughing pump to get things going. The initial pumpdown and cleanup, CAN be done with a high vacuum, but it is actually more efficient in both time and effect, to use either a low pressure inert gas glow discharge (He or Argon but even N2 will do) to scrub the fusor's interior parts or a high pressure hot fill of super dry gas. The number of impacts per second on the walls and parts n pieces inside is what cleans it. So either high pressure, or high temperature accomplishes this. The high temperature outgassing effect will take... high temperatures... red to orange heat and a few minutes to few hours depending on thickness. This happens best with the first couple runs, as far as the inner electrodes are concerned. Heating the shell to 900 C is just not in the cards for most people, so we live with some outgassing there.

In most cases, the absolute amount of contamination contributed by outgassing and miscellaneous debris, is probably a small percentage of that which comes in with the gasses. PPM level purity still has micron level partial pressures at atmospheric pressure and these ratios will hold (more or less) thoughout normal fusor operating cycles.

So.. bottom line is... while the sophisitcated high vaccum equipment is nice to have, and absolutely necessary for electron gun experiments and such, for the simple fusor, you barely need it. Understanding this can be very important when you are working on a tight budget.

Dave Cooper

[Steven Sesselmann]

Thanks guys, for pointing out that not every "hare brained" idea is worth persuing.

It would be interesting to know if two concentric spherical grids with a large potential voltage difference (in space) would pull in and trap some positive ions, and what would happen. it would be like an artificial "gravitational" field for charged particles.

Maybe in the ionosphere...could there be enough ions and a low enough pressure there?

Could we send up a balloon filled with D2 and containing a fusor grid inside the balloon?

Please tell me to stop wasting my time!

Steven

[Frank Sanns]

Steven,

Believe it or not, you idea in space would work WITHOUT and enclosure vessle if only ions would last. If you took some deuterium (or any other gas) into space and released it as ions, the electric field of the fusor would trap the ions indefinately EVEN WITHOUT CONTAINMENT. The electrostatic force is far greater than the kinetic forces that make the ions want to escape into the vacuum of space. Unfortunately, ions have this very bad habit of neutralizing when the come near any source of electrons which turns out to be just about everything. Once the neutralization happens the electrostatic force dissapears and the deuterium escapes into space.

Now if only you can find some magic dust to prevent the recombination of ions, then your idea will work just dandy!

Frank S.

[Steven Sesselmann]

Frank,

Furter to our previous speculations...,how about a fine mesh outer grid, made of a radioactive material with a very long half life.

Any deuterium atoms trying to get through the grid, would be ionized by the radiation, sending the positive nucleus back in towards the inner negative grid. Alternatively something like a Thorium mantle covering the outer grid.

That way very few atoms would escape.

Steven

[Chris Trent]

It seems to me that the primary issue here is trapping some of those pesky little electrons. If they just roam about free then you're fighting a loosing battle.

Just about any electrons coming in from outside will be drawn to the outer grid. So far so good, but you get the inner grid hot and it'll be spewing out electrons to boot. Now if you had another positively charged grid around the inner cathode you might could catch most of those too. It probably wouldn't work at higher pressures without arcing but in space it might just do the trick.

Add a mass spectrometer type system to funnel just the DT ions into the system and things start to look interesting.

[Richard Hull]

Forget ever ionizing any D2 atoms anywhere with thorium or any low specific activity radioactive isotope, espcially at fusion pressures. The MFP is just too great. A pure matallic thoriun fusion chamber wouldn't even come close to ionizing a recognizable amount of D2.

Richard Hull

[Steven Sesselmann]

Okay Richard, point taken...it's always good to run these ideas past you guys with more experience.

Just another idea for the waste paper basket i guess.

Steven