Anode layer ion source. Operation pictures

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

Post by Andrew Seltzman »

I've only tried to focus the beam by varying the pole pieces. I might try electrostatic/magnetic focusing later on, but my next step will probably be getting the injectors producing short pulses of ions (<100us).
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

There has been some success with pulse work on the injectors

The injectors were run at 10mTorr with an air plasma. HV bias to the anode ring was supplied using a behlke GHTS60(opt1) high speed mosfet pulser http://www.behlke.com/pdf/ghts.pdf capable of delivering up to 15A pulses at 6kV with down to 100ns pulse width. The injectors were found to require a few ms to ionize once HV bias was applied to the anode ring, with a couple of ms jitter. The pulser has 250ohm in series with the output. A 1k resistor was placed in series with the anode ring, a 1k resistor was placed in series with the injector case to monitor injector current, and a 1k resistor was placed in series with the faraday cup to measure beam current. A high speed camera was used to observe the plasma discharge.

On the oscilloscope trace, ch1 is the gate signal to the HV pulser, ch2 is 1v/ma injector current monitor, ch3 is 1v/ma beam current monitor, ch4 is anode HV. beam current peaks at 0.3A
10mtorr.png
A high speed camera was used to observe the plasma discharge. These are from ~3ms long discharges
at 420fps
pulse420.png
at 1000fps
pulse1000.png
With the 1k resistor in series with the anode removed at 10mTorr, beam current peaks at 0.55A for about 10us with a subsequent exponential decay. (average of 16 pulses)
10mtorr_pulse.png
Jitter in the ionization delay is currently limiting the minimum pulse width, but work is in progress on that front as well.


By the way does anyone know where to get krytron tubes?
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Richard Hull
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Re: Anode layer ion source. Operation pictures

Post by Richard Hull »

Krytrons are dual use devices and are not long lived. Hydrogen thyratrons might be better and more available surplus and can repetitively handle pulses over a long period with 100 amp pulses easily to be had in the 4C35 and the 5C22 can handle hundreds of amps. The one or two krytrons I have were obtained at hamfests over the years as well as the 40-50 hydrogen thyratrons I now have. You probably could not even dream of acquiring either the Krytrons or the H2 Thyratron new. I note the 5C22 was over $1000.00 in an old Newark catalog. Most of the 5C22's I have were under $5.00 at hamfests.

Many of the surplus H2 thyratrons are timed pulls from radars and special precision pulsed energy setups where temporal jitter is crucial. Once the jitter gets out of spec for their app, the perfectly functioning, (save for jitter), tube is pulled.

You may buy a "pig in a poke" at a hamfest in a $5.00, 5C22. I will note I have never found a burned out filament in one of these monsters. Shake the tube and see if stuff rattles around in the tube. (metal particles). Note it is perfectly normal to see a blackened ring inside the envelope around the screened area near the top. All have green transitional uranium glass flat tops where the anode exits. Check the long glass anode stem for cracks that have let out the magic.

If you are not constantly pulsing at a high rep rate in formal daily service, I have pumped 1kiloamp pulses through these puppies and they can take it on the chin.

Specs on 5C22

http://www.relltubes.com/filebase/en/sr ... tional.pdf

I note e-bay has a ton for sale ranging from $10.00 to this brand new National Electronics tube which is what you get from Newark sold here for only $750!

http://www.ebay.com/itm/NATIONAL-ELECTR ... _33wt_1361

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

I'm almost out of the welded version anode rings (which were left over from the initial injectors made for my fusor) since the ion sources have been selling well. The anode ring on the ion source had to be re-designed due to problems finding a machine shop willing to mass produce the TIG welded version(0-80 threaded rods tig welded into a ring) on the mass production ion source.

The resulting design uses three 0-80 flat head screws countersunk flush into a custom machined anode ring. The new design is much easier to mass produce and just as stable(in mounting position) as the older version. I ordered 60 anode rings shown below and have assembled the next batch of ion sources.

Anode ring top/bottom
SAM_6062a.jpg
Ion source with new anode design
SAM_6061a.jpg
Ion source with new anode design
SAM_6065a.jpg
Batch of 6 new ion sources using the new design
SAM_6063a.jpg
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Re: Anode layer ion source. Operation pictures

Post by Silviu Tamasdan »

I have a quick question about the design. What is the purpose for the central rod to be bored? Is it so it can be used as a gas inlet? Or does it influence the magnetic circuit?
There _is_ madness to my method.
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

The central "rod" is actually a screw, the hole is a vent to prevent trapped gas from forming a virtual leak when the source is screwed into a conflat base plate.
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Re: Anode layer ion source. Operation pictures

Post by Silviu Tamasdan »

Oh I see. It's a "virtual" vent. :)
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

I recently started a company to sell these ion sources, spread the word to anyone who is interested. For amateurs on fusor.net, I will extend a discount for now, and sell these for $250ea.

https://www.techplasmas.com/

ALIS.jpg
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

I have recently developed a technique to allow narrow pulse width, high current ion pulse generation with reduced jitter and delay in an anode layer ion source by adding a keep alive electrode into the discharge channel. I have a patent pending on this design, and a paper on this technique under review in Review of Scientific Instruments(attached below)

RSI paper(under review)
https://drive.google.com/open?id=0B28CX ... nkxQXdkS1U

Keep alive electrode cross section
KA3.png
KA electrode closeup
Still0009png.png
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Re: Anode layer ion source. Operation pictures

Post by ian_krase »

Cool - I assume that runs a "simmering" low current discharge?
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Finn Hammer
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Re: Anode layer ion source. Operation pictures

Post by Finn Hammer »

Andrew,
Please excuse my presence in this very advanced thread, but I have been looking for an opportunity, for a while, to ask why the anode was supported by only 3 screws, leaving the 4th. hole vacant.
I guess this post answers that.

Cheers, Finn Hammer
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

Finn,

The original reason for the vacant hole was to allow a gas feed to come in through the back of the ion source, also the first ion source prototypes were hand machined, so the looser tolerances made the fasteners more likely to bind with the lower machining tolerances; only having three mounts reduced this probability. The original anode ring was also welded to threaded rods, so this would have been one less weld.
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

A patent has been granted on the use of a keep alive electrode to decrease startup time:
http://pdfpiw.uspto.gov/.piw?PageNum=0& ... LRPgD8lPts
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

I have a mass-producible base-plate design for the anode layer ion source using an aluminum cutout from Front Panel Express
IMG_20190320_235610180a.jpg
A hermeticallly sealed Pasternack PE4077 BNC connector is used as the HV feedthrough. It's rated to 500v with a dielectric withstanding voltage of 1500v, however I have run it for extended time at 1000v and shortly to 1700v without problems
IMG_20190320_235626288_HDRa.jpg
Ion source mounted on testbed
IMG_20190320_234942510a.jpg
ion source running with baseplate
IMG_20190320_235000977a.jpg

2.75" blank conflat flange outline for Front Panel Express if anyone wants to make their own custom feedthrough flanges
http://www.frontpanelexpress.com
2.75CF_outline.zip
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Re: Anode layer ion source. Operation pictures

Post by ian_krase »

Interesting that those Pasternack connectors work as high vacuum feedthroughs.

Can one realistically run one of these types of sources off an NST?
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

The pasternack BNC connectors are hermetically sealed and will hold a vacuum, though not UHV since they use an elastomer o-ring to seal to the base plate; not a real issue in the vacuum ranges that fusors/shuttering/deposition runs at though.

If rectified to DC then yes an NST would work, though make sure not to drive it with too much current.
I would not recommend an NST though since they tpically can supply much more current than the ion source can handle and can drive arcs that could damage the source.

I would recommend using an EMCO F40 high voltage DC-DC converter, it has an HV output proportional to the DC input voltage and can be controlled with a DC-DC buck converter
https://www.ebay.com/itm/EMCO-F40-High- ... xycmBSrONF
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Re: Anode layer ion source. Operation pictures

Post by Richard Hull »

I once found a fist full o' these little gems at a hamfest on small old surplus circuit boards in a giant box for a buck a board. I sold a lot of them once I removed and tested them. Most went with the huge lot of EMI PMTs I sold years ago here in our trading post. These are perfect little bias supplies as long as you need only microamps as in PMT work.

Where did I get the PMTs? At Ed Wingate's N.Y. Teslathon! (no longer held) A guy had a giant gamma camera head with about 40 or more EMI PMTs still attached with sockets wiring and preamps to a 2 foot diameter NaI:tl crystal. It think he was asking for $100 but I got it for about $80. I finally got rid of the crystal at one of my HEAS fleamarket events a few years back.

Hang around enough hamfests over the years and you find stuff like this. This will be my 41st year of hamfesting. I used to hit 13 fests a year. Alas, now it is only about 6 plus HEAS. Some of the best goodies are at HEAS as relates to my needs. (vacuum, HV, bizarre cool stuff)

I sold a bunch of these types of small bias supplies that were 0-3000v negative output at this just completed HEAS fleamarket. They all went fast. I forgot to give the schematics out. If who ever got them contacts me I will try and scan the info sheet and e-mail it to them. Just PM me.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Anode layer ion source. Operation pictures

Post by ian_krase »

OK.

What would be the mechanism of failure? Heating the magnets to demagnetization?
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Re: Anode layer ion source. Operation pictures

Post by Richard Hull »

I would imagine, like many such magnets that ferrite or Alnico would be used as opposed to rare earth where heating is an issue. Samarium cobalt can take a little bit of heat. Of course, rare earth NeFeB can be used if their energy product is high enough to put the needed field strength in the working gap where air cooling at stand-off distances can be maintained. On a commercial production basis, custom shapes can be made that would take advantage of the lowest cost type that would do the job. Ferrite tends to win out in most cases of custom formed magnets where moderate fields are demanded around hot environments to avoid additional cooling systems.

Amateurs are at the mercy of extant shapes and types of permanent magnets for experiment which are usually kludged affairs such that the resultant field shape and strength is less that optimum to just plain terrible. Still, we tend to persevere. Externally powered electromagnetic structures can, with some forethought, be fashioned to produce a good field if one doesn't mind throwing that energy away to get a good field.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Anode layer ion source. Operation pictures

Post by John Futter »

i'm sure that i posted a pic of our NW25 that has the required BNC thread to test on our helium leak tester
I'm talking about the Pasternak hermetic BNC's
Out of 20 BNC's we accepted 17 to go into stock leak rates less than 10^-14 litres per sec
viton o-ring a must with the slightest wipe of grease to aid seal
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

300C-350C is the typical upper limit for SmCo magnets.

If you were arcing a NST into the source it would either melt the anode ring or overheat the magnet.
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