Anode layer ion source. Operation pictures

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.

Re: Anode layer ion source. Operation pictures (Feedthrough flange, 30min operation, temperature data)

Postby Jon Rosenstiel » Wed Mar 11, 2009 11:45 pm

Very impressive work, Andrew. TIG welding that close to the knife edge must have been a little nerve-wracking, to say the least.

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Re: Anode layer ion source. Parts for set of 5

Postby Andrew Seltzman » Sat Mar 14, 2009 1:37 am

Cooled grid is complete and operational. Results and designs uploaded to my website.

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Final Design Modifications. Faraday Cup Measurements

Postby Andrew Seltzman » Sat Mar 14, 2009 1:50 am

Anode now has 0-80 threaded rods TIG welded into surface and sanded down to provide flat surface as opposed to screwing into nuts spot welded to back of washer.

Anode is secured by nuts on back of alumina standoff.

Spring loaded connection between HV feedthrough and threaded rod leading up to anode.

Alumina gas feedthrough added.

This is the final design, components for all 5 injectors have been machined, only 1 has been assembled.

Faraday cup data:
-------------------------------------------------
No optimization after assembly, just tested as assembled.
Faraday cup was an injector casing, 7/8" depth, 7/8" ID, current measured as voltage across 1.1k resistor, no cup biasing, no secondary supression.
Data as follows:
Icup Vsource Isource
1mA 700v 2mA
2mA 1000V 4mA

50% of source current goes into beam current.

Construction details will be uploaded to wwebsite presently.

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Re: Final Design Modifications. Faraday Cup Measurements

Postby Steven Sesselmann » Sat Mar 14, 2009 9:13 am

Andrew,

This is top quality engineering work, with a fair amount of innovation, real eye candy. Just revisited your web site again, and saw the excellent star mode images from your revent tests.

I look forward to see how the ion guns perform.

What is the maximum voltage of your current PSU, your experiments seem to be around the 15 kv mark ?

Steven
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Re: Final Design Modifications. Faraday Cup Measurements

Postby Andrew Seltzman » Sat Mar 14, 2009 7:11 pm

Maximum PSU voltage is -40kV. Voltage was limited in tests since the lack of thermionicaly emitted electrons fron the grid prevented sustained plasma below 10mTorr without ion sources. At 10mTorr, 15kV was the max voltage that could be used without drawing too much current from the power supply.

Once these ion sources are used on the fusor, pressure will be decreaces and voltage will be increaced.

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Re: Final Design Modifications. Faraday Cup Measurements

Postby Steven Sesselmann » Sun Mar 15, 2009 2:08 am

Andrew,

Can't wait to see your results..

I like your setup, the grid has two advantages, a) it is cooled, and b) it has a thick radius, thereby reducing the voltage gradient around the grid wires (less likely electron emission from the surface.)

Hope to get the stats for my Q list soon..

Don't forget to count the power to the ion guns ;)

Steven
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Re: Anode layer ion source. Operation pictures

Postby Chris Bradley » Sun Mar 15, 2009 6:47 pm

There's no mistaking this is serious, well crafted kit.

I'm still unsure about what the 'wiring diagram' is going to look like. In the fusor application, are you intending to hold the anode at ground potential, or the cathode at ground (chamber) potential? Presumably if you hold the cathode to ground then all your ions would be attracted through the centre EHT cathode and on to the ground on the opposite side of the chamber? That's why they are accelerated away from the anode in these examples, because they see a nice, lower ground potential and desire to head towards it. But if it were the anode that is grounded then you'd need to isolate the flange from the chamber to float it a little negative, upto the ion supply potential.
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Re: Final Design Modifications. Faraday Cup Measurements

Postby Carl Willis » Tue Mar 17, 2009 3:59 am

Hi Andrew,

Your skill and speed at turning these out are enviable. Nice photos, decent data so far. You'll probably get quite a bit more current out of these with deuterium than with air, all other factors remaining the same. There probably are secondary electrons coming out of the faraday cup arrangement, but the geometry should limit their number some (it is the bored-out housing of one of the ion sources if I read you right).

Nice post.

-Carl
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Re: Anode layer ion source. Operation pictures

Postby Steven Sesselmann » Mon Mar 23, 2009 6:28 am

Andrew,

Looking at your Anode Layer Ion source design and the way you use the powerful magnet, would it not have been better if you used a ferromagnetic material for the casing, rather than stainless steel?

Looking at your pictures, the casing appears to be ground, so I assume you intend to have a positive voltage on the anode ring when you use it on your fusor. Can you confirm this?

Steven
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Re: Anode layer ion source. Operation pictures

Postby Andrew Seltzman » Tue Mar 24, 2009 4:38 pm

The casing is made out of 410 stainless, which is ferromagnetic, with roughly the same properties as carbon steel. It is slightly less ferromagnetic, but probably no more then 5-10% or so. If you pull a magnet off of it, you can't tell the diffrence in force between 410 stainless and carbon steel.

The case is grounded, the electrode is held positive.

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