finding vacuum equivilant pressure- Nuclear fusion

rp181 · Mon Mar 02, 2009 6:12 pm

Hello all.
I have been doing research for quite awhile, My next project is going to be nuclear fusion (fusion, not fission! don't go on about blowing up the world, farnsworth fusor if your interested)). I am in the process of designing a vacuum chamber. It will be pumped down to at least 10^-3 torr (equivalent to .000016 PSI). How would i go about calculating the chamber pressure and if the chamber can hold it? The inside diameter will be around 6 inches. I think that you just do atmospheric pressure minus chamber pressure, times surface area of the sphere. The problem here is as walls become thicker, surface area increases. I want to try to use a polycarbonate chamber to keep it clear, but stainless steel will be used if necessary. How do i go about using material properties to calculate if it can hold?

Also, will a nitrogen regulator work with deuterium?
Thanks for the help, This has been the one thing i have been puzzling over.

sandman · Mon Mar 02, 2009 6:26 pm

I would be worried with "hydrogen enbrittlement" if there were any steel parts in the regulator.

but, i must say you have the best projects ever, i wish i was your friend

rp181 · Mon Mar 02, 2009 6:51 pm

totally forgot about that. That might not happen because it is heavier then hydrogen, though still a isotope.

JohnnyBOOM · Mon Mar 02, 2009 7:42 pm

You are really going to attempt fusion in a plastic vessel? Won't hot plasma be involved in some way? Wouldn't stainless steel be better, maybe with a heat treated quartz view port? I don't think you will want to be looking at it anyway, if you are successful...flying neutrons...ya know. I think you may also need tritium, though you can use lithium i suppose.

Full vacuum is only 14.7psi.

Hydrogen embrittlement happens with all isotopes of hydrogen. As the hydrogen diffuses through a material, it can encounter elements that will react with it. Hydrogen loves to react with carbon particularly, like in carbon steel. When the hydrogen attaches to a carbon on it's way through a material, it creates a hydrocarbon...like methane. Since methane is a gas, you end up with a highly compressed molecule of gas trapped inside the material...this induces very high internal stress. As the process of embrittlement continues over time, more and more stress is created inside the structure of the carbon containing material. Eventually it will fail.

I'm a bit interested to try this fusion concept:
[GVideo]http://video.google.com/videoplay?docid ... 9479871760[/GVideo]

rp181 · Mon Mar 02, 2009 8:57 pm

tritium is illegal and almost impossible to get, and very dangerous. Deuterium works fine. I am probably going to go with SS, but a clear chamber would be awesome =) The plasma is kept within the center isometric ball, the vacuum helps with the heat transfer. The original question still stands.

Big-E · Mon Mar 02, 2009 9:46 pm

If a manual pump is okay, look in an auto parts store. They usually sell them in the tool aisle for diagnosing vacuum leaks.

Oh, and if you want something that's not a manual pump, they make them for race cars that don't produce enough vacuum on their own (vacuum assist). Check a Jegs catalog or go to their website.

I don't know how much vac these units can pull, but it may help you so I figure I'd assist.

I know the diagnostic tool has a vacuum gauge as standard equipment too.

I seriously wish you luck, man. Nobody has been able to reproduce any fusion experiment with any success (I assume we're talking cold fusion, yes?) Not exactly my area of expertise, but I am none-the-less fascinated. An old friend of mine had a father who worked at Argonne national labs, And he tended to tell us about all the interesting research they do there. They would also give workshops and seminars for Joe six-packs like myself; a lot of the concepts just blew me away! Really cool stuff!

It's 2009; Someone should've cracked that nut by now! 8)

pharmboy · Mon Mar 02, 2009 9:58 pm

Hmmm...as far as the vacuum level you're looking to pull, odds are you'll need a two-stage system. Firstly a mechanical pump to reach moderate-low vacuum, followed w/ a diffusion pump to really pull it down. Good luck.

Big-E · Mon Mar 02, 2009 10:05 pm

Hmmm... Maybe a really, really long sealed chamber, with a piston that is pulled back by a large hydaulic ram? Maybe I shouldn't have sent you to the auto parts store!

rp181 · Mon Mar 02, 2009 10:09 pm

No, i am not trying to make any breakthrough's here, Its normal HOT fusion. Google farnsworth fusor, its been done many times, including by people my age (15).
A two stage system is the minimum, A manual pump would take ALONG time for a chamber that size. I doubt that car pumps will work, Ile look anyway.

pharmboy · Mon Mar 02, 2009 10:13 pm

Not quite, the level of vacuum required to perform fusion(not the cold variety)...can't be achieved w/ a mechanical pump of any variety(namely due to tolerances of pumps). I'd bet on finding a surplus diffusion pump from a facility that does large molecule mass-spectral analyses. Odds are, as there are few mechanical parts, they'd be in good condition, bad news, they require a special oil which is uber-expensive. I wanna keep updated on this. I'm becoming quite fascinated.

Fnord · Tue Mar 03, 2009 10:09 am

Diffusion pumps are available on ebay of of course, but you are likely to spend upwards of $100 (not including shipping).

I think you may have better luck with this on 4HV

Not many of us have experience with fusion...

And yeah, a polycarb chamber would probably result in xrays blasting outwards at all angles.

jimmy101 · Tue Mar 03, 2009 1:17 pm

As to the pressure rating of the chamber, it is just 14.7 PSIA. Doesn't really matter if you are using a cheap pump or a zillion dollar pump, the pressure on the chamber is about the same.

A $10 water aspirator will pull a chamber down to 0.4 PSIA.
A good reciprocating pump will do about 0.001 PSIA.
A diffusion or turbomolecular pump will do about 10<sup>-12</sup> PSIA (10<sup>-13</sup> bar).

The forces on the chamber are essentially identical for all three cases;
14.7 - 0.4 is basically equal to 14.7 - 0.001 is basically equal to 14.7 - 0.00001.

Many types of containers can withstand 14.7 PSIA. Most lab glassware. Pretty much anything made out of metal and designed for positive pressure applications. PVC pipe (even DWV since it's only 14.7 PSI).

rp181, if you can't figure out something as simple as the required pressure rating of the chamber a home brew Nuc is probably not a good idea.

POLAND_SPUD · Tue Mar 03, 2009 2:20 pm

a fridge compressor can be used as a vacum pump... but I don't know if they are good enough for this

yeah I know I am predictable...

rp181 · Tue Mar 03, 2009 4:41 pm

I figured the 14.7 PSI, I was just confused with finding a balance between surface area and thickness.
nuc's are not that dangerous, most obvious is radiation (easy to shield x-ray, neutron count is not that high), and high voltage (and asphyxiation if your stupid....).

EDIT: I just got a reply from a company. I might be able to get a stainless steel vacuum chamber (6" OD, 5.8" ID). There are two big ports on top and bottom, and 4 medium ports on the sides.

jimmy101 · Tue Mar 03, 2009 5:37 pm

rp181 wrote: nuc's are not that dangerous, most obvious is radiation (easy to shield x-ray, neutron count is not that high), and high voltage (and asphyxiation if your stupid....).

Uh, riiiight.

You working with an invisible toxin and mutagen that can penetrate it's container.

Have you had any radiological training?

X-rays are not "easy to shield", indeed X-rays are about the most difficult radiation to properly shield. Alpha is the easiest, the half thickness in air is only something like an inch or so, a single sheet of paper will stop most alphas.

Betas are more difficult, half-distances in air range from several feet to several tens of feet depending on energy.

Gamma's (X-rays) are very difficult. Air won't stop gammas, neither will paper.

Heck, the whole series of names; alpha, beta, gamma (equivalent to A, B, C) were choosen based on how difficult the radiation was to stop with shielding. Alpha is by far the easiest, gamma the most difficult.

The danger from an external radiation source typically roughly follows how difficult they are to stop (shield).

The danger from an internal (ingested) radiation source typically goes the other way. An ingested alpha emitter is usually the worst, followed by beta and gamma emitters.

BTW, the correct term is Gamma radiation, not X-rays. The term "X-ray" is generally reserved for lower energy electromagnetic energy created by, for example, an electron beam striking a target. A generic vacuum tube with an electron beam from an electrically heated wire and a target can generate X-rays (indeed, that's how it is done in an X-ray machine). Gamma radiation comes from nuclear processes and, though it to is elecromagnetic radiation, it is of much higher energy.