Anode layer ion source. Operation pictures

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Andrew Seltzman
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Anode layer ion source. Operation pictures

Post by Andrew Seltzman » Sat Feb 14, 2009 4:47 am

Here are some preliminary tests of an anode layer ion source that I am working on.

Anode layer ion sources (http://www.plasmalab.ru/depos_ion.htm) are simular to hall effect thrusters, except they don't require the neutralizer source.

My source is 1" long, 1.25" OD with a 0.75" molybdenum wire ring as the anode.
It uses an N40 rare earth magnet for the magnetic field.

Some of these sources can produce up to 30mA of ion emission per linear cm of emission area. (http://www.veeco.com/Products/process_e ... rodGroup=0)

In the pictures below this source was being pumped down by a direct drive dual stage pump in good condition and was operated at about 1-2kV from a power supply with 5mA max output. More data will follow.

Andrew Seltzman
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Carl Willis
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Re: Anode layer ion source. Operation pictures

Post by Carl Willis » Sat Feb 14, 2009 8:42 am

Hi Andrew,

This is an ion-source topology with (at first blush anyway) lots of interesting possibilities for fusors. Thanks for bringing it to attention with such fine craftsmanship and beautiful discharge photos. It would be one of the easier and more practically accessible ways of making radial "sheet" beams. Paired with the Jon Rosenstiel grid construction, sheet beams from anode-layer slot sources could really do a good, efficient job of putting lots of ions on unobstructed inbound trajectories with the highest possible energy.

Any idea yet what kind of lifetime this source gives you? I might imagine some heavy sputtering, and the small interelectrode spaces are vulnerable to whiskers. Just a thought.

-Carl
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Chris Bradley
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Re: Anode layer ion source. Operation pictures

Post by Chris Bradley » Sun Feb 15, 2009 10:22 am

This is a beautiful display of both craftsmanship and plasma manipulation.

I don't see any immediate issue for sputtering as I view this as essentially a plasma discharge across a small gap in which electrons can only get to the anode via a very sluggish exb drift (if they can manage it at all, magnetron condition depending) and ions mostly (?) head off in an alternate direction to the cathode anyway (else they'd have to stream against the exb drift direction to reach the cathode).

My query/comment would be over what the relative potentials here are. Presumably the plasma formed in the region is at an electric potential somewhere in the middle of the held voltage and, presuming the cathode is being held to ground, ions are accelerated by some fraction of that voltage above ground and would therefore accelerate to ground by fields extending away from the anode and off to 'the nearest' ground potential.

So in a fusor, ions emerging from this would have already energetic ions that would accelerate through the central grid, out the other side and then on, straight into a ground potential (as they have enough energy to do so). Plus electrons would happily stream into the device towards the anode and get caught up in the exb mêlée.

This is not to denigrate the application in any way, I am sure the relative merits and means to usefully operate this in a fusor setting can be established. I'm just wondering what the best way to set up the relative potentials are, to achieve the desired effect.

best regards,

Chris MB.

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Re: Anode layer ion source. Operation pictures

Post by Hector » Sun Feb 15, 2009 2:38 pm

It looks just like a small home made Hall Thruster. Very nice.

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Re: Anode layer ion source. Operation pictures

Post by FogerRox » Mon Feb 16, 2009 8:11 pm

Thanks Andrew for the update. Always a pleasure.

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Richard Hull
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Re: Anode layer ion source. Operation pictures

Post by Richard Hull » Mon Feb 16, 2009 9:14 pm

Nice stuff! This near shell ion sourcing is what the simple fusor has needed to advance a bit and, finally, some folks are getting on the job in an attempt to make it happen.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Anode layer ion source. Operation pictures (Second design + Data)

Post by Andrew Seltzman » Wed Mar 04, 2009 2:21 am

Improved anode layer ion source design.

Dimensions of casing and magnet type remain the same.
The casing is now fabricated out of alloy 410 stainless steel (magnetic alloy) instead of 1038 steel. It is a little harder to machine but retains the rust/corrosion resistant properties of stainless steel with the magnetic properties of carbon steel.

It is noticeably more granular when machined, creating chips and short strings with rough edges as compared to the long smooth strings when machining 304/304L stainless and is difficult to get a shining surface finish even when machined with sharp carbide tooling. It is possible to smooth/polish the surface with sandpaper/scotchbrite.

The anode is now constructed out of an 18-8 stainless shim (non-magnetic) with 0-80 nuts spot welded to the back. 0-80 screws insert through 1/8” OD 1/16” ID alumina rods to hold it in place.
The ring is held in a more consistant position resulting in a more even ion beam distribution.

Operation data:
Pressure unknown, estimated in the mTorr range about 5-10mTorr
Voltage Current
500 1.6mA
700 3.6mA
900 5.7mA
1000 7.5mA

In the mtorr pressure range, about 60-70% of total current goes into ion beam current.
Attached is a paper describing anode layer ion source operation


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Carl Willis
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Re: Anode layer ion source. Operation pictures (Second design + Data)

Post by Carl Willis » Wed Mar 04, 2009 2:48 am

Hi Andrew,

Thanks for the update on this interesting ion source.

I'm curious, do you feed gas in during operation? Your drawing has what might be a Swagelok-type fitting, though it's hard to tell.

Your numbers are for air ions, correct? Do you plan on running it with a fusion gas?

What do you use to measure current?

-Carl
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Re: Anode layer ion source. Operation pictures (Second design + Data)

Post by Mike Beauford » Wed Mar 04, 2009 2:50 am

Very nice work Andrew. Question, how long do you think the anode will last and how long have you been running it for?
Mike Beauford

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Re: Anode layer ion source. Operation pictures (Second design + Data)

Post by Andrew Seltzman » Wed Mar 04, 2009 3:12 am

That cad is of the final design, the sorce is running without active gas feed at ambient chamber pressure.

In the final design HV will be supplied to each injector through an MHV feedthrough, and gas through a swagelok fitting through one of the ceramic tubes through the base of the injector.

Anode life is unknown, however after several minutes the source is barely warm.
It will arc above 1kv with the current anode (the shim), most of the pitting is from that. From what I have read, they will operate reliably for a long time.

Andrew Seltzman
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Andrew Seltzman
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