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uzzors2k

Wed Apr 01 2009, 09:48PM

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

Some of you may remember Peter's thread about an "Electron beam in air". (See his website or the thread.) The idea is to use a particle accelerator with a thin window on one end to allow accelerated electrons to exit the accelerator. Recently I've become completely enthralled by the idea, and I've looked into it. I can only find one hobbyist level Linear Accelerator on the enitre Internet, made by Fred Niell eons ago, which is sad. However it goes to prove that it is possible, after all, these things were made 80 years ago! I take it the major difficulty is the glasswork involved and evacuating the tube to sufficiently low pressure.

I think aquiring a low vacuum is possible to do on the cheap. For one thing Fabio seems capable of aquiring a fairly low vacuum using a "common" A/C pump and getter.

Pumps like his go for 100-500USD, which isn't awful. And if an A/C pump is too expensive a few A/C compressors in series should work just as well according to this site. What I'm wondering is if the pressure could be lowered enough using some getter and an A/C pump/compressors? Maybe enough for a Crookes tube, but how low does the pressure need to be for an accelerator? My reasoning would suggest that as the pressure is lowered it would take less getter to remove the remaing gas molecules, so this should be possible with enough getter. If this is true it would work fine?

As for glasswork... I doubt this is even remotely simple. Is there any low cost way to fabricate a small accelerator tube with proper seals and the like? How much eqipment would it take to "do it right", and is it even reasonable for a hobbyist to construct something like this? I imagine the window would be the most difficult section. What about getting it done by a professional glassblower, assuimg you provide the electrodes and such? Someone with this guy's skill could certainly do it.

All I wanted to do with this thread is bring the idea to attention, as it doesn't appear out of reach for a well equipt experimenter, and you've got to admit it's got a pile of nerd-cred attached. I just want to see someone do it! Is anyone here able to make one? Does anyone know an easier way to do it?

3l3ctrici7y

Wed Apr 01 2009, 10:20PM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

In a book I got a while back about various electrical/HV projects to do, it talked about constructing a CO2 laser using common neon lighting parts. It uses the long glass tubes, and the electrodes used for the neon signage. The text suggested that its fairly easy to do. I was shown around a neon glass bending shop one time, and saw a guy bending the glass, had a glow tube, to blow into it to keep the inner wall from collapsing and so forth. It looked fairly straight forward, though, he did have a fairly large propane torch/flame/burner.

I'm not sure what scale size of glass you're wanting to work with, but if its in the regime of neon signage, you should have an abundance of parts to chose from, including electrodes, and its all intended to be easy to bend and fuse. Though, looking at TDU's setup, I think neon will be just about right :)

Hon1nbo

Wed Apr 01 2009, 10:37PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

glass work is not that hard, at least for this kind of work (making figurines gets tricky) - sealing the electrodes should be fairly strait forward, but the key thing to watch out for are the wall thicknesses, and the annealing of the glass (which helps to determine it's strength)

as for another accelerator, a basic one can be found at rtftechnologies.org

the guy above also builds IEC Fusors...

rp181

Wed Apr 01 2009, 11:33PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

For a vacuum pump, you may be able to try these:

Keep in mind that in some similar compressors like this, they are capable of 600PSI.
They are from AC units, putting some in series may give a high vacuum. There price is very good, and there are many in stock. I know for a fact that people have put them in series to get more than 2000 PSI output, while each individual one is not designed to go more than 300PSI.

I have been contemplating building a fusor for the past year now, and am in the process of obtaining parts. I have almost got my hands on a turbomolecular pump (10^-14 torr capable) and a SS vacuum chamber.

Good luck.

Hon1nbo

Thu Apr 02 2009, 02:17AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

rp181 wrote ...

For a vacuum pump, you may be able to try these:

why are you referencing their ability to Compress, are they good for Vacuums?

rp181

Sat Apr 04 2009, 10:07PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Those compressors are deigned to be used in a closed circuit, so it will work both ways.

Bored Chemist

Sun Apr 05 2009, 09:27AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

It's not really my field but I just wonder about that.
If I were making a refrigeration compressor I would chose a lubricating oil that was a good lubricant and didn't get upset by the freon (or whatever). I wouldn't bother to think about the vapour pressure of the oil.
I would also use spring operated valves because they are robust and efficient.
Also, whatever sort of system I used, I wouldn't worry too much about the absolute maximum available compression ratio- as long as it was high enough to get the refigerant to condense, that would do.

If I were making a vacuum pump I would chose the oil differently. I'd use flap valves and I'd make sure that it was full of oil so it had no dead volume at the end of the pump stroke.

Now there are plenty of stories out there about people using salvaged fridge compressors as vac pumps and they show that the pumps work just fine.
But the ability to compress to a high pressure is no indication of the ability to produce a good vacuum.

The best vac pumps are things like Ti sublimation; oil diffusion, and ion pumps and none of these will generate any real pressure; they all need a pretty good vacuum before they start.

uzzors2k

Sun Apr 05 2009, 10:13AM

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

You're correct about fridge compressors, BC, and from numbers I've seen on various websites they can only achieve a vacuum of about 1/10 of atmospheric pressure. A/C pumps however, are used to dehumidify air conditioners making them capable of vacuums in the range of 1/10000 of an atm or better. Many use 2-stage rotary vane pumps and can do 1/40000 of an atm. I've found a source of them here (Norway) for a decent price, along with borosilicate glass. If I can pawn off my moped I'll give glass blowing a shot this summer.

Oh, for reference these sites are great for learning the basics of scientific glass blowing. Teralab and ECU.

jpsmith123

Fri Apr 17 2009, 05:30AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Hello Uzzors,

This topic is one I'm interested in too. It's something I'd like to discuss further and actually try someday.

In the mean time, Harbor Freight sells a 2 stage 3 CFM rotary vane vacuum pump for $150.00 USD. If you could get one of their 20% off coupons, you'd get it for $120.00...that would be a good deal, IMO.

That pump, and a two stage trap made with, say, shredded copper (e.g. chore-boy scouring pad) to block oil backstreaming, and a molecular sieve to trap water vapor, may get you down low enough in pressure (e.g., electron mean free path comparable to or somewhat larger than tube dimensions) to accelerate a beam and bring it out into the atmosphere.

BTW, I've plated titanium with a few different metals by hydriding it electrolytically first, and I understand that indium based solder will wet and stick to glass, so flashing the titanium foil with copper plate and then using indium solder to secure it to glass or ceramic might work.

For a cathode maybe a field emission source might work...maybe something like this:

Regards,
jpsmith123

Proud Mary

Fri Apr 17 2009, 06:02AM

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

Uzzors wrote ...
I can only find one hobbyist level Linear Accelerator on the enitre Internet, made by Fred Niell eons ago, which is sad. However it goes to prove that it is possible, after all, these things were made 80 years ago! I take it the major difficulty is the glasswork involved and evacuating the tube to sufficiently low pressure.

Sorry Eirik, for some reason I didn't notice this thread, or your question before.

A very full account with diagrams of making a "home-made atom smasher" (a linear accelerator for electrons and protons) by FB Lee is given on pp 344-360 of The Scientific American Book of Projects For The Amateur Scientist Simon & Schuster, New York, 1960.

I can send you the whole book as a 20MB .pdf file if you have trouble getting hold of it yourself.

The book also contains instructions for building an X-ray machine powered by a DIY Oudin coil. The Oudin coil construction description is that much more interesting than the X-ray part, which you'll find rather primitive compared with our own work.

There is a much more interesting article on how to build a cloud chamber - not the popular dry ice demonstration experiment, but a serviceable piece of equipment capable of being re-set any number of times without the need for costly fresh materials etc.

It is something I intend to build when I have finished Thor.

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