Anode Layer Ion Source Mod?

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
David Kunkle
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Anode Layer Ion Source Mod?

Post by David Kunkle » Mon Jan 23, 2017 8:32 pm

hjuklghjk 002.JPG
One of Andrew's ion sources arrived here Friday. Got to thinking exactly how I was going to mount this. What if it was mounted/welded directly to the front of a CF or NW nipple? In the photo, the weld would fill the gap between the ion source and the inside of the CF nipple. This would force all input gas thru the ion source and eliminate piping from the gas input connection to the source. It would just be an open space behind the source for the gas to be fed into. It would also eliminate the standoff. It might make connecting the HV spring to the source a little trickier to install. It would have to line up and keep contact with the source as the back flange is being mated and sealed. Easily checked for continuity after assembly with a DMM.

Andrew Seltzman
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Re: Anode Layer Ion Source Mod?

Post by Andrew Seltzman » Tue Jan 24, 2017 1:34 am

I would recommend going with a non-welded method. Consider using a viton o-ring between the source and the nipple, that would effectively seal the source, and hold it in place due to the elastic nature of the o-ring. A gas feed going through the source is not required for operation, it will ionize the neutral background gas and form a good beam between ~15mTorr down into the 0.1mTorr range(this is how I use them on my fusor)

Consider using a hermetically sealed bulkhead BNC of MHV connector as well(bulkhead mount with o-ring, not the welded type)
Not sure how high in voltage this will go in a vacuum, but it is pretty cheap
http://www.ebay.com/itm/Pasternack-PE46 ... Sw14xWOsEK

Also something like this could be drilled/tapped for the standoff:
http://www.ebay.com/itm/2-75-4-Pin-Plas ... SwHMJYLxs2
Andrew Seltzman
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David Kunkle
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Re: Anode Layer Ion Source Mod?

Post by David Kunkle » Tue Jan 24, 2017 8:08 pm

I thought an o-ring would get too hot there. I'll have to find the right size and try that first. Lot less permanent than welding it. In light of that, I already have an extra CF blank that I'll use for the base. Took it to the weld shop this a.m.

I noticed a long time ago it looked like it would simply recirculate the gas from the chamber the way it was made. The o-ring should do the trick. There are a few times I will want to have the vacuum lower than the gas pressure to the source.

Thanks for the tip on the bulkhead BNC and the plastic feedthrough. Anybody know what kind of plastic they use for those? Mostly curious, but hey, you never know. Wouldn't be hard to fab something out of a sheet of that.

Is the alumina gas feed just loose between the input fitting and the source?
Wondering why there is one hole left in the anode?

Thanks.

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Re: Anode Layer Ion Source Mod?

Post by Andrew Seltzman » Tue Jan 24, 2017 10:40 pm

If you choose to go with welding, the casing material is 410 stainless in case they ask. Viton o-rings can get pretty hot without problem.

I run my injectors ionizing/recirculating the ambient deuterium. This will typically will work well unless you have a large impurity source/outgassing.

The plastic on that base plate on ebay looks like PEEK, though I can't verify that

The alumina tube in the injectors with baseplates is loose(not o-ring sealed) in the 4th hole in the ion source base, but mechanically retained with the snap rings, the conductance through the tube center is much higher then the conductance around the ~0.001" clearance between the tube and injector so gas would flow thought the tube into the injector.

The remaining hole in the anode was part off the original design of the injectors to accommodate welding a 4th threaded rod to hold the anode ring, however this was found to be unnecessary as the 3 threaded rods in the current design hold the ring in position accurately.
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David Kunkle
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Re: Anode Layer Ion Source Mod?

Post by David Kunkle » Wed Jan 25, 2017 3:36 pm

Got it all. Thanks.

May have given the wrong impression. Took the flange to the weld shop to have the holes drilled and tapped- no welding. Not a big fan of working on SS. Main problem is probably cheap drill bits and lack of enough lubrication in the past.

Ordered a few different size Viton O-rings from o-ring store online. One should fit well. Looks like Viton is good to about 400F.

Grainger has everything from rod to sheet stock in PEEK in case anybody cares. Must be one of the better plastics for vacuum use? Good to 480F. Now that I look closer at the prices, SS is looking pretty cheap. A measly 6" X 6" X 1/2" thick piece is $350! Anyone for a 48" X 12" X 2" piece?- a mere $16,000.00.

Got curious and went to Wikipedia: "Because of its robustness, PEEK is used to fabricate items used in demanding applications, including bearings, piston parts, pumps, HPLC columns, compressor plate valves, and cable insulation. It is one of the few plastics compatible with ultra-high vacuum applications. PEEK is considered an advanced biomaterial used in medical implants. It is finding increased use in spinal fusion devices and reinforcing rods. It is extensively used in the aerospace, automotive, and chemical process industries.[6] PEEK is often considered a high-end engineering plastic, such as delrin, PTFE or nylon. "

I see the snap ring on the gas tube now in the one photo on your website.

Any point in filling in that 4th hole? - or should the gas coming out of there get ionized as well?

Andrew, I can't find it now, but did you post some info on power usage and % ionization for these?

Thanks.

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Re: Anode Layer Ion Source Mod?

Post by Andrew Seltzman » Wed Jan 25, 2017 4:48 pm

Any chance the weld shop could TIG welds a MHV connector into the flange for you? There is no need for an external gas feed so just having them weld in the MHV connector would give you a first rate base plate for the injector.
You can get them for $38 on lesker
http://www.lesker.com/newweb/feedthroug ... ?pgid=weld

There is no need to fill the 4th hole, it does not affect operation.

About 50% of the current into the injector goes into the beam
viewtopic.php?f=12&t=5011&start=20
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David Kunkle
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Re: Anode Layer Ion Source Mod?

Post by David Kunkle » Tue Jan 31, 2017 3:21 am

The shop had already drilled the base plate, etc., so I stuck with my original plan.
Now that it's been fired up, the 4th hole doesn't appear to affect it like you said.
My source is at about 1kv, 5 ma, and 5 mTorr in the pics. Still playing with settings. No Viton o-ring installed yet. Can't feel any heat generated after several minutes, so o-ring should survive just fine.
Camera's not great- best I could get.
dxufhjig 005.JPG
ghikmh 001.JPG

John Futter
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Re: Anode Layer Ion Source Mod?

Post by John Futter » Tue Jan 31, 2017 6:11 pm

David
no at that drive it will only get warn 1kV x 5mA = 5 watts
Its when you start accelerating the ions so same source but 60kV and 20mA that things start getting vey hot very quick in this case 120 watts and you get a minute or two before the magnet overheats and the source stops all by itself. We use a kerosene cooled copper block inside the anode layer source to keep the magnets cool which allows operation up to 100kV @15 -20 mA ie 1.5 -2 kW of heat

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Re: Anode Layer Ion Source Mod?

Post by David Kunkle » Thu Feb 02, 2017 5:52 pm

5W- hadn't thought of it in those terms yet. About the equivalent of a turn signal bulb in a Buick.
If I recall, I started getting some intermittent arcing when I tried to go over 2kv. Don't think the little alumina insulators would care for 60kv let alone 100! ;)

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Re: Anode Layer Ion Source Mod?

Post by John Futter » Fri Feb 03, 2017 1:06 am

David
no the ion source only has 1 -2 kv across it the rest is 58kv of acceleration
I use self bias of the source to get the 1-2kV which is stolen from the terminal voltage applied in today's case 60kV
and I'm running the source at between 3 and 12mA so thats 180 to 720 watts and yes the samples being hit by ions get very hot. The ion source has 4 gallons per minute of kerosine cooling that is heat exchanged with our chilled water circuit I use a petrol bowser pump to shift the kero around the cooling circuit

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