Bake-out procedure

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
Sarvesh Sadana
Posts: 48
Joined: Mon Aug 22, 2016 9:55 pm
Real name: Sarvesh Sadana
Location: Fremont, CA

Bake-out procedure

Post by Sarvesh Sadana »

How does one do a proper vacuum chamber bake out?

I am thinking of simply wrapping the chamber in aluminum foil and using a heat gun to evaporate all of the water vapor while pumping. How well would this work?

I have Viton CF gaskets from Duniway.
User avatar
Nick Peskosky
Posts: 135
Joined: Wed Aug 08, 2012 9:02 pm
Real name: Nicholas Peskosky
Location: San Diego, CA

Re: Bake-out procedure

Post by Nick Peskosky »

I'm sure this has been answered before on this forum else a cursory search with your favorite search engine spits out:

http://gescott14.blogspot.jp/2007/12/uh ... e-out.html

https://www.pfeiffer-vacuum.com/en/know ... /bake-out/

https://www.researchgate.net/post/Can_y ... to_bakeout
(read the answers to the original question in this post)

https://www.duniway.com/images/_pg/vito ... orings.pdf

Long story short, you heat the chamber up extensively while pumping via internal quartz lamp or external heat gun/heating tapes... take care not to exceed the published temps for Viton Gaskets (stay <200C) by measuring your surface temps with a thermocouple.
Nick Peskosky
NPeskosky@gmail.com

"The whole of science is nothing more than the refinement of everyday thinking." - Albert Einstein
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Bake-out procedure

Post by Richard Hull »

Unless you are shooting for 10e-5 or lower, the classic, hot tape bakeout is of little value. In general, you want to only heat the interior. Bombardment will do a great job of forcing water and trapped gases from the interior shell. It will also heat the entire device as well. The glow will contain some UV light as well and this is a bonus. The shell is bombarded with electrons and neutrals, this causes the heating. This is classically called glow cleaning.

Turn on your mechanical pump and it will pump to a certain level X, (50-10 microns, usually), turn on the fusor power supply and take the voltage up to a voltage and current where the grid glows red orange and hold there while the system pumps. Leave it there and up the voltage and current as needed to maintain the glow. Leave the mechanical pump's ballast open. This may take a hour or two the foreline and chamber pressure should rise at first and then drop. Next start your diff pump or turbo and run it until the glow on the grid extinguishes. Now you are fairly clean and ready for fusion.

Warning!!! Once the diff pump oil reaches near the boiling point of water you will need to be mindful of the glow and the current as water will be pouring into the system if any is in the diff pump oil or pump walls, itself. You may have to back off the voltage and current to maintain just a dull orange glow. Do not melt your grid!

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
prestonbarrows
Posts: 211
Joined: Sun Jun 24, 2012 1:27 am
Real name:

Re: Bake-out procedure

Post by prestonbarrows »

Richard has already summed it up well.

Baking out is of marginal utility on an elastomer sealed system. Firstly, you can't reach the ideal temperatures. Secondly, the elastomers tend to quickly permeate back in whatever you expelled during the bakeout process. A 'proper' bakeout will push the chamber up towards a few hundred C, literally to the point where the stainless steel is visibly glowing.

If you are dead set on baking your system out, you should think about using copper conflat gaskets. A heat gun is not very efficient for this task but would work to some extent. Most of the power will go to the room rather than the chamber. If you are using an insulating jacket, the hot air needs to be injected between the chamber wall and the insulator which you will find to be difficult in practice.

The best method is to use heater tapes designed for this purpose. This is basically a resistive wire wrapped in refractory fiberglass. Having this or another heat source in direct contact with your chamber and surrounded by an insulator like aluminum foil or fiberglass is the standard method.

That said, there is certainly a benefit to conditioning a system. Simply running a plasma discharge inside the chamber is almost always the best way to go for a hobbiest fusor. Both the incident particles and UV will efficiently knock adsorbants off surfaces.
Jerry Biehler
Posts: 975
Joined: Tue Nov 24, 2009 3:08 am
Real name:
Location: Beaverton, OR

Re: Bake-out procedure

Post by Jerry Biehler »

What? No, no, no.

Bakeout works just fine on rubber sealed systems. 150C with heat tape and you can get down into the --7 and -8 without any problem. I have done this on many systems.

Stainless will not glow anywhere near several hundred C.

Though a heat gun is just not going to do it. The silicone heat tapes are the best option, wrap around the chamber a few times and cover with aluminum foil. I have an external box with an omega temp controller and put a thermocouple under the heat tape someplace and set it for about 150C. Thats good enough for most applications.

Putting a quartz halogen or small mercury discharge lamp in the chamber works well too. I put a 1kw tungsten lamp in my big chamber (26"x30") and it cooks it out pretty well.
Post Reply

Return to “Vacuum Technology (& FAQs)”