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Insulating Vacuum Spacer Fittings

Posted: Wed Apr 21, 2010 9:18 pm
by lutzhoffman

Does anyone know if any company makes standard NW, ISO, or KF fitting compatable insulating rings / fittings? I am asking because this would be an ideal path for me to finish the design for my ion source.

The top part is basically a copy of Doug's published microwave design. Then I had found some real neat SS fittings on ebay which had gas inlets, compression fittings, etc. altready in them, they were already 50% of an ion source. The last design hurdle is that I have to put the extraction electrode at -3KV, and I also want to add an additional focusing electrode which will float at an adjustable 4 - 20 KV for some other experimental reasons as well. The "clean" easy way to do this would be to use an insulating glass, silica, or ceramic spacer, which will mate with standard vacuum fittings. Alumina ceramic screws can hold it all in place, so that part is easy.

Does anyone know of any source of any "off the shelf" insulating spacers, with o-ring grooves etc? I am trying to avoid having to make my own if possible due to it being a general pain to machine glass / ceramic material, let alone finding the right size of stock.

A last resort would be to try to cast one out of the same HV epoxy which is used to make some ion implanter accelerator tubes, and then lap it, or finish it on a lathe or something. Ebay has had large 150mm ones out of silica, but nothing which will mate to NW 80-100 size standard vacuum fittings.

I figured that it was worth posting this because such an item could be very handy for fusor contruction, and other uses also. Thank You....

Re: Insulating Vacuum Spacer Fittings

Posted: Wed Apr 21, 2010 9:41 pm
by Linda Haile
Is this for an ICP or CCP source, Lutz?

Re: Insulating Vacuum Spacer Fittings

Posted: Wed Apr 21, 2010 9:54 pm
by DaveC
Lutz -

You are most likely aware of the Insulator Seal Inc. company, which is a std source of metal flanged, insulating spacers. You can seen them on the MDC website. But their stuff is fairly pricey for the amateur.

Glass/pyrex tubing and compression seals come to mind. also. These are much more modest in cost, although not exactly what you might need

Making the spacer from pyrex with epoxied on end pieces might also work, if it doesn't get much above 80-90C.

MACOR is fairly expensive, although it is not difficult to machine... Carbide or even HSS tools work well. But it makes a gritty mess on your machines, and not every shop will agree to handle it.

MACOR flanges require a little thought here. A CF flange with an elastomer gasket, will work, as well as an O ring seal. This would again keep your maximum temperature limit to around 100C, or less


Dave Cooper.

Re: Insulating Vacuum Spacer Fittings

Posted: Wed Apr 21, 2010 10:43 pm
by Carl Willis
Hi Lutz,

Plastic centering rings for KF and ISO are made. I can't find them at Lesker, but for Europeans, Trinos carries various kinds of insulating centering rings and clamps: ... ptfe-.html

My only experience with plastic components is when they are shipped from the manufacturer as a cheap included part with turbopumps or other vacuum systems (usually with a cheap buna o-ring to boot). So no endorsement of their insulating capabilities from me. The plastic is usually black, probably implicating carbon black in the mix. The kV range is pushing it I'm sure.


Re: Insulating Vacuum Spacer Fittings

Posted: Wed Apr 21, 2010 10:49 pm
by lutzhoffman
Thanks for the tip! No I was not aware of insulator seal inc, I will check it out for sure. If I cannot find an off the shelf item, I may just get a bored out pyrex / silica blank from united lens, which is easy, and then buy a couple of diamond bits, and mount the combo with 2 captive viton o-rings in mild compression.

As far as if this ion source bing an ICP, or CCP, I would lean towards it being CCP because it is tuned via an adjustable brass screw stub which protrudes into the cavity around the quartz tube.

Interesting question though, I just never had a reason to give it much thought to be honest. In the microwave realm the normal Rf ion source coupling coil etc. is absent, and replaced by a waveguide. In this design its a simple short coaxial line stub which brings the microwaves from the magnetron to the cavity.

Doug could shed more light on this aspect, I never gave it much thought because I already know that it does the job very well, after reading his references. Check out the forum thread on this source, and the design on his web site. These microwave sources can deliver a single charge species, into the 90%+ range which is simply wonderful. Not to mention its extreme efficiency, when compared to traditional more power hungry RF source.

Mine will be inside of a 30-90PSI HV terminal some day, so the power generated by the in terminal generator, which is driven by an insulating shaft, is limited to about 1kw, and thus precious. At first I was going to use a 400Hz alternator, but try to find one. So instead I am going DC with a low RPM wind generator type of setup. My extraction HV can then be from DC-HV solid state converters like the 12V - 2-3KV /10ma neon ones, and the CCFL inverters. The main power will now be from an inverter to run the maggie.

Re: Insulating Vacuum Spacer Fittings

Posted: Wed Apr 21, 2010 11:23 pm
by Linda Haile
I wasn't sure to what extent you were copying Doug's design. I believe Doug said that, even with his design, quartz is a lot better than pyrex.

Re: Insulating Vacuum Spacer Fittings

Posted: Thu Apr 22, 2010 12:02 am
by lutzhoffman
No worries I was only planning to use pyrex as a possible insulating spacer material because its cheap, can handle some temp. and I know where to get it.

For the discharge tube portion of the source its quartz all the way, had a long discussion with Doug on this one because I had considered Alumina, Doug sold me solid on Quartz for all the right reasons.

The discharge tube portion of my source will be an off the shelf quartz ball joint socket stub. The bottom bell of the stub will seal to the SS assembly that I got on ebay with the built in VCR gas fittings, and a built in gas channel leading to where the quartz tube attaches. These socket stubs are like 20 bucks, and thick walled enough to handle some external pressure, the best part is that they are available with a built in o-ring groove on the bottom of the bell. I have attached a pic so that it makes more sense.

Re: Insulating Vacuum Spacer Fittings

Posted: Thu Apr 22, 2010 2:04 am
by John Futter
Look at the following pics carefully
We use PETP plastic for insulating breaks
first photo shows breaks in beamline and ancillaries on target chamber
second photo shows +40kV break on our gas ion source again PETP.
Third photo shows the connection to the target holder which can be taken to -40kV.
so with this we get + 40kV from the ion source and post mass selection acceleration of another 40kV from the bias of the target holder so a total of 80keV implantation depth.

We have no trouble sealing the PETP to CF flanges but Iso's need the centering ring.
I.e. the plastic is just a flat surface for the vac seal. Knife edges bite into the plastic and seal and of course iso o-rings have no trouble.

Re: Insulating Vacuum Spacer Fittings

Posted: Thu Apr 22, 2010 8:26 am
by lutzhoffman
Thanks John....

The pictures tell the story, that is a pretty awesome setup that you have there. Sometimes simple cheap materials can provide perfectly serviceable solution. This does make perfect sense. I suppose the eventual decision will have to be determined by the operating conditions. When I get closer I now plan to run the ion source for some time, and then monitor the temperature of its different areas. If the temps are OK then I may try this or another polymer. If I remember correctly this is a partially crystallized version of PET which is used in plastic bottles. Just out of curiosity is there a particular set of properties, or machining properties, which influenced the selection of this polymer? -or- will any of the harder insulating polymers work? I did get the idea of the conflat flange seal knife edge seal. Thanks

Re: Insulating Vacuum Spacer Fittings

Posted: Thu Apr 22, 2010 8:46 am
by John Futter
I looked at the hour meter on the setup today
its just short of 1000 hours of ion source running. Its had two cleans that I know of, ie a rub with fine emery 900 grit to clean the in vacuum insulating surfaces.
Ion source runs about 2 mA beam current with many different ion beam types most of them metals or semiconductor type ions.
base pressure is about 3 by ten to minus 8 millibar ( it takes about two weeks of pumping to get to this level when new plastic bits are introduced)

Most of the bits you see started out as MACOR but ham fisted students and others broke them and saw these parts made in plastic in a hurry, that have stayed

hope this helps