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GluD

Fri Apr 17 2009, 06:48AM

Registered Member #1221 Joined: Wed Jan 09 2008, 06:17PM
Location: Odense, Denmark
Posts: 196

Borrosilicate glass is rather dificult to work with in my opion, I'd suggest you to try soda lime glass instead, I havnt tried it myself but I heard it should be easier to shape as you wish.

Hazmatt_(The Underdog)

Fri Apr 17 2009, 07:36AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

If soda glass is available it might be worth a shot, and you can see if you can get some from a sign shop and electrodes and whatnot. That's the only cheap way of getting what you need.

If you went with boro you need a lot of equipment, and sealing electrodes to boro is a real pain. It requires a hard metal like Tungsten and a graded seal of Schott glass or UO glass, and great care while beading the feedthrough wire.

Here in the states I doubt I could get soda glass tube as the majority of the glass vendors sell boro, but see what's available first.

For vacuum your first stage will need to go down to 70 microns to support the next pumping stage, that is a hard minimum requirement. That will support an oil diffusion pump ( oil costs $1 per cc ouch! )
If you use an oil diff stack you will need a cryo trap to freeze out the water and possible oil contamination. PTFE seals also prevent oil creepage into the high throughput manifolds. Unfortunately you cannot put anything in the free path to stop oil particles as this will prevent you from pumping down.

After that you will need a Ti pump, or ampules sealed into the apparatus of Al Ca Ba Mg and other metals that you can fire with an RF coil.

You will need various poppett valves, o ring seals, kwik flanges, thermocouple gauge tubes, and a high vac magnetron gauge tube or ion gauge tube.

It should all run just under probably $4000, heh.

It's no small feat. Just getting a thermocouple gauge tube and meter costs well over $250, even for a beat up old one.

I recommend going to a university and asking for stuff they don't want. You may be able to get an entire pump cart that way, with valves, gauges, and diff stack. That's how I got some stuff, so try that, sure beats paying for it.

Hopefully a college nearby is throwing out a mass spectrometer, that would really help you out. They even come with their own LN2 trap to grab the oil particles.:

Lethal Shot

Mon Apr 20 2009, 03:42PM

Registered Member #1623 Joined: Tue Aug 05 2008, 03:31PM
Location: The Netherlands
Posts: 39

I've been looking into making one of these someday myself. I've done some reseach and it seems it isn't a huge technical problem constructing them. The biggest problem with particle accelators are accelerating ion's or giving particles a high energy potential. I've never begon on the project because I couldn't find a vacuum pump which is affordable for me (I'm from the Netherlands). There is a document on the internet which covers all the basic's of particle acceleration and the problems involved. Its a very good document only it is a bit hard to read through because there's a lot of math in it, but its worth it. The document can be downloaded here:

jpsmith123

Tue Apr 21 2009, 03:50PM

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

There are several different approaches to accelerating a beam of electrons and extracting the beam to the atmosphere...books could be written about the subject.

If I ever get around to trying to do it myself, I will probably go with some kind of short-pulse driven system. This is largely because pulsed systems can withstand much higher voltage gradients than systems operating with continuously applied high DC voltages, and this makes for a physically small "electron diode" and associated apparatus.

I've seen quite a few papers on pulsed electron diodes where, for example, a tesla transformer charges up an intermediate-storage blumlein, which then discharges through a spark gap switch into a diode - the diode having a remarkably small volume, even at multi-megavolt voltage levels.

Here's an example of an industrial device under development which is supposedly capable of a 60kv, 1kA electron beam, yet it's only 5mm in diameter:

jpsmith123

Tue Sept 08 2009, 11:56PM

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

Well I've now accumulated about 3 or 4 journal papers wherein a "dual resonant pulse transformer" (DRPT) is used to drive a pulsed "electron diode", and I must say, it seems like relatively simple (in some cases almost "crude") apparatus is generally involved. (There's also one interesting paper I've had for a while wherein the HV source is a spiral generator

Anyway, here's my subsequent thought:

What about using, say, a coaxial resonant cavity as the "secondary" tuned circuit and a capacitor and spark gap (and associated inductance) as the primary tuned circuit?

I know that resonant cavities have been used in accelerators for a long time, but I'm not aware of any example whereby an enclosed coaxial resonator was used in a manner exactly analogous to the tuned secondary of a DRPT.

I haven't done any calculations or simulations yet as I'm just sort of thinking out loud.

In any case, if it is actually feasible, it seems the advantages would be that vacuum insulation could be used in the cavity and there would therefore be no insulators exposed to the HV; i.e., the end of the center conductor could be the cathode, thus the resonator itself would also be the electron diode.

Scott Fusare

Wed Sept 09 2009, 08:30AM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

Have you seen the Lenard tube project mentioned on the Fusor forum?

More detail (in German) here -

jpsmith123

Wed Sept 09 2009, 12:51PM

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

No I hadn't seen that before. Very interesting!

There's some interesting stuff in the discussion there as well, including this paper:

What caught my eye was this statement:

"The goal is to build and test a prototype e-beam tool, capable of being transported in a humvee type vehicle, which has a range of at least a hundred feet and a beam density adequate to deactivate moderately shielded electronics within a few seconds."

They plan on projecting an electron beam for at least 100 feet?

BTW, here's a company that sells cathodes and e-beam guns and hardware:

plazmatron

Wed Sept 09 2009, 06:05PM

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

I was thinking about Lenard tubes just a couple of days ago!

Recently I have been putting together a high Vacuum, on the cheap, (and I mean dirt cheap, since I`m poor!!)
I had already invested in an inexpensive Javac rotary vane pump off evilBay, for Â£150 last year, so I will be using this as a roughing pump. I managed to buy a diffusion pump of evilBay for ~Â£5 recently, and I have just set about making flanges and manifolds for it.

Unfortunately you cant get lower and lower pressures just by series-ing up refrigerator pumps.
The ultimate pressure is determined by the pump oil itself, and the fact that once you get to 15 microns or so, air no longer behaves as a fluid, but rather a bunch of molecules just bouncing around, that may eventually wander into the pump and be removed.
The idea works with refrigerator compressors, but only to a point. They pull a horrid vacuum to begin with (~ 100mbar) , and the compression ratio is too low. There is no way any amount of them would pull the 15 microns of a good rotary vane pump. The air conditioning Javac pumps off eBay are ideal, but you really need a diffusion pump to get into proper high vacuum. Do not be tempted to evacuate the exhaust of these to attain lower pressures (like with the fridge pump), since it will decrease the pumps ability to lubricate itself.

Diffusion pumps can be had very inexpensively, so there is no reason that high vacuum should be out of anyones reach. There is no technical mystery to them either, they are remarkably simple devices. All my manifolds are being built out of copper and brass plumbing fittings (modified), and brass plate. Cu and Brass being easy to solder and work, even with my modest compliment of tools.
The hardest/most expensive thing about diff pumps is getting hold of the oil. Most suppliers want you to buy at least half a litre minimum, when it costs about Â£1000/gallon! For a small pump you only need 50ml or so, so obviously this is a bit of a pain!

Anyhow, once the pump is assembled and running I will be doing a write up on here, for anyone wishing to get into high vacuum. And if I end up having to buy a half-litre of oil, I will be happy to decant the remainder into 50ml bottles, should anyone want to buy any, without having to take out some kind of pact with the bank!

As for a Lenard tube, well thats top of the list! I see no reason why an Aluminium foil window cant be used, with adequate support, and personally I would go for a demountable tube, rather than sealed glass for an endevour like this.

Les

Proud Mary

Wed Sept 09 2009, 07:29PM

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

The Scientific American Book of Projects for the Amateur Scientist (Simon and Schuster, 1960) p. 350 has an "atom smasher" linear accelerator with an end window of 1/4" aluminium plate, in which is cut a haxagon of 37 3/16"* holes to support aluminium foil of 0.001"thickness.

The target for bombardment with beta particles, or protons (when the tube is filled with H2) is held just outside the tube window.

*It is unclear to me, from the .pdf copy I have, whether this is 3/10th" or 3/16" inch.

Conundrum

Wed Sept 09 2009, 07:31PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

I recall reading somewhere that the contents of heat packs are Fe powder and activated charcoal. can you see where this is going :)

in theory, heating the compound in a poor vacuum should scavenge at least the oxygen, resulting in a cleaner vacuum..

then there's the "plasma window" ...

otoh, a piece of pyrolytic graphite might well be useable as a makeshift electron emitter, as a small quantity of nanotubes should be present.

-A

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