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Diffusion pump project

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plazmatron

Mon Oct 12 2009, 05:42PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Steve McConner wrote ...

I recently found an Edwards vacuum coating machine in the uni's junk pile, and it looked to me as if it just used a length of plastic hose between the diffusion pump and the backing pump. The clear stuff with the reinforcing braid.
I never figured out a way to dismantle it or get it off campus without getting in trouble, and it's now been rained on.

Thats a shame! They are very cool toys! I manage to get two off of evilBay for just a few pounds, so I`m all set up.

Yes reinforced PVC is often used for the backing connection, since outgassing on the low side is minimal, and the rotary should be able to handle it. Often a spring is pushed up the pipe to stop it collapsing under vacuum.

I will be modifying the rotary pump connections again, by having two 10mm pipes going into a 15mm. Microbore is still much too thin for my liking, plus I want to get the 3inch pump up and running too, which will require the backing bump to pull at least 85l/min, so I need much larger diameter tube, and shorter connections.

Les

uzzors2k

Wed Oct 14 2009, 02:31PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Awesome! Your project is truly inspiring. I had no idea diffusion pumps could be found so cheap, I'll have to keep an eye out for one. Are you going to try glass-blowing with this setup?

plazmatron

Wed Oct 14 2009, 06:58PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Uzzors wrote ...

Are you going to try glass-blowing with this setup?

Yes, I am, I have been playing with soda glass tubing, however I still need more practice to get up to a reasonable standard.
I also need a better heat source too. I have just got a Neon sign catalogue, and their prices for neon sign electrodes seem reasonable, and also come with sealing stems too, however I will practice some more with scrap glass, before purchasing some.

For the time being, most of my experiments will be done in demountable chambers. This is dead easy, since there are hundreds of candidate chambers kicking about, for example the glass rolling pin shown in the previous posts, and just today, I was using a small Salmon paste jar! These little jars are great, as they are very thick (4mm), and easy to drill holes in. I built an experimental Lenard tube today with one. It worked for a short while, until the electron beam punctured the Aluminium foil window

More voltage, and less current next time I think!

Les

uzzors2k

Wed Oct 14 2009, 09:16PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Great stuff, can you post some pictures of your Lenard tube?

I've found a source for both a little shop vac like the Javac you have, and borosilicate glass here in Norway. I'm debating whether I should get into this now or wait until I'm done my studies at the moment. Seeing you doing this is really tempting me!

Proud Mary

Thu Oct 15 2009, 12:32AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Eirik, finish your degree or you'll end up hanging out on corners in downtown Oslo!

BUT - since the true enthusiast can never really be deterred - you may not know that you can produce all kinds of interesting soft X-rays at the pressures obtainable by the Javac alone by plasma discharge.

The problem for most folk is that unless you have a pal in Brighton who will send you a Ne-CH4 proportional counter tube with opposing Be windows,* it's pretty much impossible to measure X-rays much less than 10keV, as I'm sure you know.

So, with the Javac, or whatever pump will get you down to 20 millitorr you could make plasma discharge X-ray tubes with Kapton exit windows for not very much money.

Plazmatron has the Devil's Luck, and you could watch and wait in ebay till the Crack of Doom and never find another diffusion pump for NOK 135.

As for these very soft rays: as well you know, the softer the nastier. I think you'd absorb about 99% of a 5keV
'mistake.' Just because they're 'soft' doesn't mean that there aren't plenty of them either.

The plus side is that shielding costs are very low indeed.

Did I send you a BPX-65? If you take the lens out, it will go down to about 2keV, and detect individual X-photon strikes with nearly 100% percent quantum efficiency, the attenuation of the rays by any intervening air being a limiting factor.

Imaging, however, becomes increasingly problematic as we descend from 10keV.

* Generally valued at a good piece of reindeer sausage or dried reindeer meat....

plazmatron

Fri Oct 16 2009, 04:03PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Uzzors wrote ...

Great stuff, can you post some pictures of your Lenard tube?

I've found a source for both a little shop vac like the Javac you have, and borosilicate glass here in Norway. I'm debating whether I should get into this now or wait until I'm done my studies at the moment. Seeing you doing this is really tempting me!

Hi Uzzors,
yep, check these out:

This is a view of the foil Anode. A 5mm hole is drilled into the base of the jar, and the foil, is imply superglued over it!
This is ordinary household foil, and the 5mm window can easily support the high vacuum.

This is a view of the tube running. The blue glow, is a result of a thin layer of electron sensitive phosphor sprinkled on the window.

I made a shorter tube today, and finally observed the emerging electron beam first hand!
This tube was sprayed black, as the light from the filament easily washes out the dim glow.

The dim blue "jet" exiting from the centre of the tube looked to be about 10mm long, at 80kV, however there was significant light in the room.
Shortly after taking this photo, the Aluminium window punctured again, I think its time to invest in some Titanium foil, and give that a shot.

I`m with Harry on this one, do complete your studies, but, at the same time, always keep an eye out for cheap bits and pieces as they show up, I'm not that lucky!

...

Fri Oct 16 2009, 05:43PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

That is amazing :-o

A little ebay searching turned up some 9um (.3mil!) thick Ti foil, I wonder if it would hold to 15psi or not

Otherwise you can get the 3 mill stuff

What are you planning to do with this new toy?

plazmatron

Fri Oct 16 2009, 06:20PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

... wrote ...

That is amazing :-o

A little ebay searching turned up some 9um (.3mil!) thick Ti foil, I wonder if it would hold to 15psi or not

What are you planning to do with this new toy?

Thanks for the link, I was just having a dig myself!
9Âµ should be easily able to handle the the pressure, the window is only 5mm diameter after all.
I hear that ordinary kitchen foil is around 16Âµ so 9Âµ in Ti should be ideal.

Well the diff pump will be used for allsorts of vacuum work, the Lenard tube was something of a diversion

But, since it is a very interesting diversion, it will have to be scaled up a little. I figure a 250kV tube would satisfy my curiosity!

Les

uzzors2k

Wed Oct 21 2009, 06:57PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Hi Harry, you did indeed send a BPX-65 over, along with some organic gas Geiger tubes for lower energy X-rays. I just need a gigaohm resistor and some time off for Christmas before I make a counter with them. It'll be fun/scary to see how much radiation leaks from my X-ray setup. Those Javacs go for the same price as a cell-phone, so they won't set me back too far. After seeing this it's hard not to jump into it, but I'll stick to my studies for now, if for no other reason than that darned polyprojectilitus which has me still doing projects I planned years ago!

That's too neat Leslie! Have you considered irritating plexiglass to see whether you can make Lichtenberg Figures? Maybe not near the same scale as Bert, but shouldn't it be possible granted you use a thin sheet and lot's of irritation time?

klugesmith

Thu Oct 22 2009, 01:46AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

plazmatron wrote ...
9Âµ should be easily able to handle the the pressure, the window is only 5mm diameter after all.
I hear that ordinary kitchen foil is around 16Âµ so 9Âµ in Ti should be ideal.

Nice work. I guess the thread is drifting from diffusion pumps to Lenard tubes.
So, though this is probably preaching to the choir:

A foil too thin to span a 5mm hole, may be able to span a dense array of smaller holes.
Here is one patent about supporting and heat-sinking a large foil window for electron beams, using finely spaced parallel fins on the vacuum side. Check out the figures:

These guys spanned a 38mm window with 0.002" (51 Âµm) Al foil, by making a simple but very strong attachment between the foil and its supporting rim.

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