Fusor in a stainless dustbin with a plastic lid

For posts specifically relating to fusor design, construction, and operation.
derekm
Posts: 140
Joined: Thu Dec 06, 2007 4:25 pm
Real name: Derek Mitchell
Contact:

Fusor in a stainless dustbin with a plastic lid

Post by derekm » Wed Oct 06, 2010 6:26 pm

The idea is more refined than that but it has the essentials.
HV feed throughs and view ports and end flanges are things we need on a Cylindrical fusor and this is an idea to provide all three at one go using a combination of ideas from this forum.
The body of the fusor is a SS tube over a base plate. The top is an transperant acrylic end plate with the HT cathode mounted directly in in the centre.
The acrylic can't stand heat and can't stand plasma.
The HT cathode is liquid cooled to stop heat from the cathode
The acrylic plate has a anullar glass plate suspended below it on thin SS tube standoffs. The glass plate stops short of the cathode by 10mm and the ss case by 10mm. The cathode has an alumina tube surround (T/C case) with a glass or ceramic disc part way down the alumina tube arranged so the plasma cant see the gap between the anular glass plate and the alumina tube through to the acrylic end plate.

This idea embodies the sacrificial glass plate for view ports
the alumina tube for cathodes
and liquid cooling.

Should the glass becoume conductive ( a problem mentioned elsewhere) this shouldnt be an issue since there is aleast 10mm of vacuum between the glass and HT and the glass and ground.

What have i forgotten. -- Oh yes you need excess pumping capacity for the acrylic out gassing.

comments?

DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 5:13 am
Real name:

Re: Fusor in a stainless dustbin with a plastic lid

Post by DaveC » Wed Oct 06, 2010 7:40 pm

Derek -

If I understand the physical relationships, correctly, it seems worth a "go"...

The acrylic will outgass at all temps, but if your pump is big enough, you can probably maintain low pressures sufficient to at least get a demo going.

If you could lay hands on a piece of tempered plate glass, and get it bored to size for your HV feedthrough, you could at least side step the outgassing problem.

The real hazard with glass-like materials, is their low thermal conductivity. Many times lower than metals. This makes them susceptible to very high localized temps, if electron or ion bombardment happens. Bell jars are very convenient for some types of experiments, but have this issue, as well.

Sounds like you're making a good start. Wish you well with the next steps..

Dave Cooper

Starfire
Posts: 1482
Joined: Wed Oct 24, 2001 6:14 pm
Real name:

Re: Fusor in a stainless dustbin with a plastic lid

Post by Starfire » Wed Oct 06, 2010 7:56 pm

Build it and see.

derekm
Posts: 140
Joined: Thu Dec 06, 2007 4:25 pm
Real name: Derek Mitchell
Contact:

Re: Fusor in a stainless dustbin with a plastic lid

Post by derekm » Wed Oct 06, 2010 8:02 pm

The glass annular shield in this is sacrificial so hot spots arent too bad . at higher powers most of the glass annulus can be replaced with a sheet stainless annulus with a smaller hole covered by a glass disk.

the key advantages of Acrylic are its cheap, transperant and can be drilled and tapped for the various bits and pieces. especially if its 20mm thick

I think I have excess pumping power in an edwards Diffstak 63, (115 l/s) with a pfieffer Uno 5 backing pump(5 m3/hr). Roughing is an Edwards E2M18 19m3/hr.

And of course I can always replace the acrylic end plate with a SS plate when I have worked out whats what.

Dustin
Posts: 105
Joined: Tue Jul 27, 2010 12:40 am
Real name:

Re: Fusor in a stainless dustbin with a plastic lid

Post by Dustin » Wed Oct 06, 2010 10:39 pm

I have an acrylic viewport 20mm thick covering an area of 100mm X 120mm and love it,
It sits on an o ring in a groove and I easy pull 10-6 and have not noticed outgassing but I don't have a valve to seal off. I have a sacrificial poly carb shield. I can't even see any distortion in the surface reflection under vacuum over this large area.
Good Luck.
Steve.

derekm
Posts: 140
Joined: Thu Dec 06, 2007 4:25 pm
Real name: Derek Mitchell
Contact:

Re: Fusor in a stainless dustbin with a plastic lid

Post by derekm » Thu Oct 07, 2010 11:16 am

This is over a 260mm aperture (I 've bought a new ISO 250 by 580mm high full nipple to provide the SS cylinder) . I thought a 25mm thick piece would work.

User avatar
Rich Feldman
Posts: 1307
Joined: Mon Dec 21, 2009 11:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: Fusor in a stainless dustbin with a plastic lid

Post by Rich Feldman » Thu Oct 07, 2010 4:42 pm

25mm is generously thick for that diameter.

This DIY solution looks a lot like your design.
http://4hv.org/e107_plugins/forum/forum ... post_79819
The builder figured that a 1/2 inch acrylic sheet was strong enough, but he chose 3/4 inch for less deflection, and a strength safety factor of over 20 before drilling.

That thread also has a picture of a semiconductor-equipment loadlock cover spanning over 300mm, made of polycarbonate only 22mm (7/8") thick. And a link to online strength-of-materials calculator that can do bending of round flat plates.
All models are wrong; some models are useful. -- George Box

John Futter
Posts: 1604
Joined: Thu Apr 22, 2004 2:29 am
Real name: John Futter
Contact:

Re: Fusor in a stainless dustbin with a plastic lid

Post by John Futter » Thu Oct 07, 2010 6:55 pm

Derek
Acrylic is fine ie perspex
Polycarbonate tends to sublime ie evapourate. I found this out when I made some sacrificial viewport protectors out of polycarbonate 2 of at 2" diameter 0.125" thick. Vacuum would not go below 1 x ten to the minus 6 millibar until I took them out where upon the vacuum went back down to 4 by ten to the minus 8 millibar. This is a twenty litre chamber pumped by a 1000 L/sec turbo.

derekm
Posts: 140
Joined: Thu Dec 06, 2007 4:25 pm
Real name: Derek Mitchell
Contact:

Re: Fusor in a stainless dustbin with a plastic lid

Post by derekm » Fri Oct 08, 2010 5:40 pm

Any implications in having a 31 litre fusor chamber as opposed to more common 1 ~ 2 litres?

User avatar
Carl Willis
Posts: 2841
Joined: Thu Jul 26, 2001 11:33 pm
Real name: Carl Willis
Location: Albuquerque, New Mexico, USA
Contact:

Re: Fusor in a stainless dustbin with a plastic lid

Post by Carl Willis » Fri Oct 08, 2010 6:14 pm

Hi Derek,

Outgassing, permeation, and adsorption all increase with chamber surface area, degrading the quality of the vacuum unless pumping speed is also commensurately increased. However, I don't anticipate you would have difficulty evacuating your planned 31-liter volume to fusion-suitable pressures using a Diffstak-63. The role of the diffusion or turbo pump for typical fusor operation is pretty undemanding, serving mostly as a speed booster in a pressure region where the forepump's speed is near zero.

One thing to consider, if the fusor chamber is indeed literally going to be a "dustbin," is the quality of the metal. I see a lot of "stainless" articles in kitchen and home-improvement stores that look nice, but are a poor grade of stainless that is magnetic and nickel-plated. (Sometimes I wonder if they're even technically stainless steel underneath). Also, check for longitudinal seams that could be mechanical weak points or leak sites. Make sure no other coatings (e.g. clear lacquer) are on the metal.

-Carl
Carl Willis
http://carlwillis.wordpress.com/
TEL: +1-505-412-3277

Post Reply