Vacuum Box Design

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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mvanwink5
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Re: Vacuum Box Design

Postby mvanwink5 » Sun Apr 21, 2013 11:12 am

I think I need a basic sanity check, is the vacuum system capital cost all in the vacuum pump equipment, flanges, and instrumentation, with the tank cost peanuts?
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

D Tibbets
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Re: Vacuum Box Design

Postby D Tibbets » Thu Apr 25, 2013 3:07 pm

Tank / vacuum vessel construction is a straight forward process. Stainless steel plates and a good welder is all that is needed.A draftsman/ engineer might help. Using surplus items like a large cyclindrical pipe may be reasonable. Aluminum may not be appropriate due to outgassing and sputtering issues. A second surrounding tank is not needed. The Neutron shielding water could be contained in a a stack of milk cartens. Actually, a pit would probably be used. Even without water tanks, the earth would moderate and absorb the neutrons. A few feet would suffice. X rays and possible P-B11 gamma rays may be more of a saftey issue that needs careful considerations.

By far the most cost effective approach would be for a University or large lab to take on the challenge. They might have almost all of the needed structures and equipment as surplus or idle equipment. The vacuum chamber is only the start. The electromagnets and power supplies will be huge challenges, even converting surplus MRI super conducting magnets as M. Simon suggested would probably be loaded with problems that would need to be resolved. A community effort would need 10's of millions of dollars along with access to considerable donated expertise and supplies if anything past WB8 scaled efforts was pursued.
Such a community, open driven approach would need a rich funder, and of course the bureaucracy could quickly get out of control.

Dan Tibbets
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mvanwink5
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Re: Vacuum Box Design

Postby mvanwink5 » Thu Apr 25, 2013 5:58 pm

Sounds academic. Sanity checks require $.
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mvanwink5
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Re: Vacuum Box Design

Postby mvanwink5 » Fri Apr 26, 2013 8:18 pm

The point is that if tanks and magnet support costs are small relative to the vacuum pump capital costs, then reducing vacuum pump costs significantly are key. Vacuum system costs, I strongly suspect, could be reduced with intelligence, by taking advantage of ion kinetics. If not, then the vacuum tank cost is not strategic (even if it is expensive). On the other hand, if alphas generation from fusion are the dominant waste gas that requires exhausting, then electrostatically directing them into exhaust chambers would be important for major cost reduction.

There may be other means of reducing vacuum pump costs. Cold traps?

But at some point, no $ input, no strategic thinking.

Low capital $ means lower risk and easier investment. Unless one is still thinking in terms of a science project...
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

mvanwink5
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Re: Vacuum Box Design

Postby mvanwink5 » Fri Apr 26, 2013 9:07 pm

"then electrostatically directing them into exhaust chambers." Sounds like an ion gun design...
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

Jccarlton
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Re: Vacuum Box Design

Postby Jccarlton » Sun May 26, 2013 10:04 pm

Vacuum design is more art than science. First of all designing for molecular flow requires an entirely different way of thinking. The gas is no longer helping you pump. It's more like catching molecules as pool balls with the pump face as the pocket. The reason pumps are so expensive is that they are incredibly precise and tend to be fairly delicate. Here's a Leybold turbo pump of the kind I would be looking at for a polywell application:
https://leyboldproducts.oerlikon.com/pr ... x?cid=1730
While I didn't register to get the actual price based on quoting smaller turbo pumps, I'm gon to guess that the these pumps cost on the 10k- 20k range. Now you could use a smaller pum, but that means that you have a smaller "pool pocket" and much sloer pumping speed, which may not be accpetable for a polywell

mvanwink5
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Re: Vacuum Box Design

Postby mvanwink5 » Mon May 27, 2013 12:19 am

jccarlton, thanks for that suggestion on vacuum pump selection, approximate cost, and the need for vacuum system design expertise.

It makes sense that there is a lot of art to vacuum system design, including the vacuum pump selection. In the case of the polywell it would seem to me that there are some special opportunities that would facilitate a vacuum system set up. In particular, I was wondering if, considering the gasses will be alphas before becoming helium, if the alphas could be steered to a collection chamber, then use a cold trap to help retain the collected gas for the vacuum pumping. Surely since the alphas are leaving via the cusps, that should be possible, no? So, as part of the vacuum vessel design it seems to me that advantages of polywell geometry and predictable and steerable alpha exhaust could divert the exhaust to the vacuum pumps. Perhaps the system could be modeled?

PS I suspect helium is normally much more difficult to exhaust than nitrogen, but that is just a guess.
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

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Re: Vacuum Box Design

Postby KitemanSA » Mon May 27, 2013 1:06 pm

If we use a direct conversion device, the alphas will be striking one face of the slats in the "venetian blind". Could that face be covered by a loose sheet of graphene or the like (sealed around all the edges but one)? I envision the ions passing easily thru the sheet and then picking up their electrons and becoming too large to fit easily back thru the sheet. Thus the tube formed by the sheet and the slat would conduct the gas to a waiting manifold (unseal edge) where it can be efficiently pumped away.

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Re: Vacuum Box Design

Postby mvanwink5 » Mon May 27, 2013 1:42 pm

KitemanSA,
That is certainly a creative approach. Thanks for that.
Best regards
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

hanelyp
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Re: Vacuum Box Design

Postby hanelyp » Mon May 27, 2013 4:38 pm

As I understand the "venetian blind" style collector:
- ions (nominally) pass between the blinds of lesser energy,
- turn as they approach blinds or final collector of higher energy,
- Ions then hit the back side of the blinds with highest potential less than ion energy.

If you can somehow fit it in without ruining direct conversion geometry, the back side of the blinds would be a good place for vacuum pump inlets. Short of that, cooling the binds aggressively might help vacuum pumps behind the blinds.
The daylight is uncomfortably bright for eyes so long in the dark.

mvanwink5
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Re: Vacuum Box Design

Postby mvanwink5 » Mon May 27, 2013 5:34 pm

The venetian blinds designs that I have seen are not for polywell and seem to assume a large spread in alpha trajectories. However for polywell, the ions have very distinct exits at the cusps and should be amenable to directing with electrostatic plates like vacuum tubes use. That would also help reduce the effort to exhaust the reactor fusion alphas/helium gas. No?
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.


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