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### Vacuum Chamber

Posted: Tue Oct 29, 2013 1:08 pm
I recently received a small x-shaped vacuum chamber from someone. It contained something that looks like an old ion-gun. When I browse the forums on vacuum chambers, it seems everyone uses a cylindrical or spherical chamber with a diameter of at least 6". My question is would a chamber with a diameter of 2.75" leave not enough room for the Deuterium nuclei to accelerate?

Sorry for no pictures, It won't let me post them.

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 3:20 pm
Ions do not need room to accelerate. They need potential gradients. If you have a deep enough vacuum, huge gradients can be suffered over very short distances. Electrodes a meter apart in a vacuum or only .01 meter apart in a deep vacuum can both accelerate their ions to the same velocity with 10kv applied.

The fly in the ointment is what level of vacuum will allow maximized fusion at a given voltage in the this case and can you insulate well enough to avoid arcing? Distance between high gradient electrodes in any environment is generally considered good insulation.

You will have more trouble getting you HV into the fusor chamber than worrying about acceleratory distances.

People here have done fusion in 2.75 inch conflat crosses, but that is about the limit and you won't be doing much fusion, either.

Richard Hull

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 3:31 pm
Richard Hull wrote:The fly in the ointment is what level of vacuum will allow maximized fusion at a given voltage in the this case and can you insulate well enough to avoid arcing? Distance between high gradient electrodes in any environment is generally considered good insulation.
Actually, I've found the problem is the reverse of this, because at typical fusor operation you're at the knee of the Paschen breakdown curve where this effect reverses.

There have been a few attempts at small fusors. Here's the problem: At the conditions for fusor operation, you actually need higher pressures so that the 'pd' is sufficient to allow for enough gaseous breakdown to create a glow discharge. You actually end up with increasing insulation with decreasing distance between electrodes once you are below a pd of 1000 micron.cm. (A fusor is typically operating around 100 micron.cm, so you can see the insulation will increase with decreasing inter-electrode space).

The consequent problem is that you need to raise the pressure to get a glow discharge in a smaller chamber, but in doing so you enter viscous flow regime quicker than you gain achievable voltage, the net effect being that you need a larger chamber to get MFPs sufficient that there is a high enough population of ions circulating.

This seems to be the reason for the limit for smaller chambers, in my humble estimation.

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 3:38 pm
Ok thank you for the fast responses. Seeing as this is my first attempt at fusion, i will probably just find a larger chamber and maybe use this one for a future project.

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 3:42 pm
The bottom line is, do you just want to do fusion, get into the neutron club on the easy and then cut out? If so, 2.75 inches is fine. If, however, you want to do serious fusion work and go over the 1 mega-neutron per second mark, then you might consider the smallest size as being 6-8 inches in diameter. These are the realities and optimum size as seen here via experiment. Larger chambers allow for easier neutron detection methods due to increased fusion capabilities. (More fusible nuclear fuel in a larger volume at any pressure or voltage.)

Richard Hull

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 3:46 pm
Richard Hull wrote:The bottom line is, do you just want to do fusion, get into the neutron club on the easy and then cut out? If so, 2.75 inches is fine. If, however, you want to do serious fusion work and go over the 1 mega-neutron per second mark, then you might consider the smallest size as being 6-8 inches in diameter. These are the realities and optimum size as seen here via experiment. Larger chamber allow for easier detection methods due to increased fusion capabilities. (More fusible nuclear fuel in a larger volume at any pressure or voltage.)

Richard Hull
Well, I don't just want to prove fusion and write about it on my college applications then get on with my life. I stumbled upon a fusor a few months ago and have been very interested in it since. I would like to eventually get up that level of fusion, but It would make sense to start small, since the project is due in May.

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 9:58 pm
In my opinion if you have the money and want to put in the effort to scrounge for parts, I see no reason why you cant't build a bigger fusor now. In the end, it will ultimately save you money. Are you doing the project for school? Is that why its due May? I suppose you could build a fusor in 6 months, however I have been studying fusors for a year and a half and just finished my demo. With all my studies I still do not understand every piece of equipment in a fusor. A lot goes into a fusor.

Good luck with your project, I wish you luck!

Scott Moroch

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 10:50 pm
Scott Moroch wrote:In my opinion if you have the money and want to put in the effort to scrounge for parts, I see no reason why you cant't build a bigger fusor now. In the end, it will ultimately save you money. Are you doing the project for school? Is that why its due May? I suppose you could build a fusor in 6 months, however I have been studying fusors for a year and a half and just finished my demo. With all my studies I still do not understand every piece of equipment in a fusor. A lot goes into a fusor.

Good luck with your project, I wish you luck!

Scott Moroch
Yeah that's what I was thinking about the money saving thing. It is for a school project, but if I do not finish it in time, I would just continue it on my own and present what I have so far. The main conflict that would stop me from completing it in May is the money. I have a very limited budget since I can't really work enough hours given my schedule. I have been checking ebay and calling around to save as much money as possible, but I haven't had much luck yet except a roughing pump I bought at a flea market.

### Re: Vacuum Chamber

Posted: Tue Oct 29, 2013 11:52 pm
If it gets close to May and you do not have enough parts and you do not have the money, then do a demo fusor. Its a look alike and you will learn a lot about what sort of plasma is created at different applied voltages and chamber pressure. A neutron producing fusor is not something you should rush to complete. There are many dangers associated with the project. For example, the high voltage is not something you want to rush to set up. If you build a demo it will save money, get the project done by May, and you will gain a lot of knowledge that will be helpful when you build a neutron producing. Also, a lot of parts from the demo system can be applied to the neutron producing fusor.

Scott Moroch

### Re: Vacuum Chamber

Posted: Wed Oct 30, 2013 1:16 pm
Scott Moroch wrote:If it gets close to May and you do not have enough parts and you do not have the money, then do a demo fusor. Its a look alike and you will learn a lot about what sort of plasma is created at different applied voltages and chamber pressure. A neutron producing fusor is not something you should rush to complete. There are many dangers associated with the project. For example, the high voltage is not something you want to rush to set up. If you build a demo it will save money, get the project done by May, and you will gain a lot of knowledge that will be helpful when you build a neutron producing. Also, a lot of parts from the demo system can be applied to the neutron producing fusor.

Scott Moroch
Yeah that's probably what i'll end up doing. Thanks for the input