Diffusion Pump

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Post Reply
Gabe Player
Posts: 3
Joined: Mon Jun 09, 2014 2:40 pm
Real name: Gabe Player

Diffusion Pump

Post by Gabe Player »

Recently I've been putting together my vacuum pump system, and I was wondering if anyone could tell me whether this diffusion pump would work?

http://www.ebay.com/itm/Edwards-Speediv ... 43cdff5df0

Thanks!
Jack Puntawong
Posts: 150
Joined: Tue Aug 28, 2012 9:10 pm
Real name: Kunakorn Puntawong
Location: Bangkok, Thailand
Contact:

Re: Diffusion Pump

Post by Jack Puntawong »

Gabe,

If I were you, I would wait a little while and spend a little more money with an air cooled diffusion pump. With this pump, you'll need to spend more money on water pumps and machine the correct adapters for your vacuum system. The adapter will also need to be machine with a groove for an O-ring because there isn't one on the pump. Wait a little more to find a better deal. For me, an ideal diffusion pump will be

1. air cooled
2. Have only conflate or NW/KF flange
3. around 4" in diameter

Jack Puntawong
Gabe Player
Posts: 3
Joined: Mon Jun 09, 2014 2:40 pm
Real name: Gabe Player

Re: Diffusion Pump

Post by Gabe Player »

Thanks! I was a little concerned about the pump, and I thought it would be best to check.
RealBorg
Posts: 27
Joined: Thu Mar 01, 2012 3:40 am
Real name: Thomas Zehetbauer
Contact:

Re: Diffusion Pump

Post by RealBorg »

If you don't want to spend a lot of money on you vacuum system, I suggest you get or build a sorption pump.

Activated carbon has a large surface with adsorption / desorption of gas molecules in thermal balance.
If you heat activated carbon while evacuating with a roughing pump most of the gas molecules are desorbed from it's surface.
When you cool it then (e.g. ice water, dry ice, liquid nitrogen) it can absorb lots of molecules and get you down to the needed vacuum range.

tom
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Diffusion Pump

Post by Dennis P Brown »

Since you are on a fusor forum I will make the huge leap of faith that your vacuum system is for a fusor - in which case an absorption pump will not work unless you can operated your fusor for very short time periods - absorption pumps are generally used on closed systems and have limited capacity when dealing with added gas.

Frankly, diffusion pumps (DP) are cheap compared to most other fusor equipment and good ones appear on ebay all the time. While air cooled is simplest, getting one of those is both a more rare find and can be more expensive (too many people want them.) I have a water cooled diffusion pump and installing water/return lines were, frankly, so trivial I wouldn't even consider an air cooled pump. As Mr. Puntawong correctly points out, however, the key part of any DP is getting one with TWO flange types you can adapt to your system easily (not just the high vac side.) Better still, get one with a manual gate valve (again, if doing fusion) because that is critical for that type of system. This, of course, is also a more rare find on e-bay (still,the very first week I looked for one, such a DP was on e-bay and rather cheap ... strange; if only I was as lucky with my homemade glass based accelerator tubes (lol)) but if such a unit is located, will be well worth the effort.
RealBorg
Posts: 27
Joined: Thu Mar 01, 2012 3:40 am
Real name: Thomas Zehetbauer
Contact:

Re: Diffusion Pump

Post by RealBorg »

I believe oil diffusion pumps are a poor choice for a fusor because they cause oil contamination and are more efficient for hydrogen than turbomolecular and sorption pumps.

Actually I am planning to operate my fusor with the activated carbon in place in the chamber.
Working Hypothesis: The surface of the active carbon can be saturated with deuterium, providing a reservoir for the sorption of other molecules and the release of deuterium.

If that doesn't work I already have 3 other ideas for achieving high vacuum:
1.) mechanical diffusion pump (momentum transfer from oil spray)
2.) thermal pump (reverse the principle of a light mill)
3.) ionization pump (use ionization and electrical potential, similar to a lifter device)

Anyone interested in discussing these ideas?

tom
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Diffusion Pump

Post by Dennis P Brown »

"RealBorg" you need to start your own thread to do this. Also, might consider changing your screen name to your proper name since that is how most here operate.
Doug Browning
Posts: 156
Joined: Sat Mar 10, 2012 9:19 pm
Real name: Doug Browning

Re: Diffusion Pump

Post by Doug Browning »

"Anyone interested in discussing these ideas?"

Sure. A new thread would be the best place though.

--------------------------------------------------------------------------------------------
"If that doesn't work I already have 3 other ideas for achieving high vacuum:
1.) mechanical diffusion pump (momentum transfer from oil spray)
2.) thermal pump (reverse the principle of a light mill)
3.) ionization pump (use ionization and electrical potential, similar to a lifter device)"


1) The usual oil diffusion pumps reach supersonic vapor speed, tough to beat. Their thermal efficiency could be greatly improved however. Occasionally see them for under $100. Oil contamination is easily solved with a cooled baffle. ( Look on Ebay, search on "CVC baffle", click "sold items" to see a long list of baffles which sold for $20 each recently)

2) Crookes radiometer in reverse? Isn't that what a turbopump does already?

3) Ionization definitely should be useable, but some limitations on vacuum level, gas load, compression ratio, and efficiency.
Post Reply

Return to “Vacuum Technology (& FAQs)”