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 » Tue Feb 07, 2017 5:47 am

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 » Mon Mar 27, 2017 3:31 am

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 » Mon Mar 27, 2017 9:18 pm

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
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

Post by Andrew Seltzman » Thu Jul 20, 2017 2:00 am

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 » Wed Sep 20, 2017 6:20 pm

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 » Wed Sep 20, 2017 6:30 pm

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 » Wed Sep 20, 2017 10:00 pm

Oh I see. It's a "virtual" vent. :)
There _is_ madness to my method.

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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman » Sat Oct 14, 2017 7:14 am

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 » Wed Nov 01, 2017 12:21 am

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 » Wed Nov 01, 2017 4:38 am

Cool - I assume that runs a "simmering" low current discharge?

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