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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Werner Engel
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Re: Anode layer ion source. Operation pictures

Post by Werner Engel »

Hi Andrew!

Great that you still work on the fusor! Thanks for all your posts - great pictures and details!

What kind of "laser density probe" do you use in this case?
Interferometry, reflectometry, scattering, refractive index?

BR,
Werner
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

Hi Werner,

It's going to be a CO2 interferometer.
http://www.rtftechnologies.org/physics/ ... ometer.htm

Andrew
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Re: Anode layer ion source. Operation pictures

Post by Werner Engel »

Hi Andrew!

Congratulations to your final picture (the one showing the interference pattern)!
It's an enormous amount of work doing this @10,6µm with all the special materials. The carbon-pipe is it really stiff enough? What about vibrations from the roughing pump? Or did you switch off pumping during the measurement? Did you choose the 10,6 due to absorption of the plasma to be expected at that density (plasma frequency) or to reduce vibration induced problems?? Thomson Scattering is done @1064 nm (Nd:YAG) at the Tokamak in Garching. It seems they do not care about wavelength. But other refractive index measurements try to use as large as possible wavelengths.
I just built a “normal” HeNe-Michelson to get comfortable with optics. But this will be adapted in several steps.

Attached a Picture of my Michelson and one of the Nd:YAGs in Garching.

BR,
Werner
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IMG_4433 small.jpg
IMG_4774_small.jpg
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

New modifications to the anode layer ion source:

The old flat anode ring has been replaces with a conical anode ring (6.6 degree inward) for better beam focusing. this should have the focal point about 3" in front of the face of the source, right at the focal point of the fusor. In reality there still is the effect from space charge repelling the beam so it doesn't focus to a point, though the beam is considerably better defined with a tighter focus.

The NdFeB magnet has also been replaced with a SmCo magnet for higher temperature operation(up to 300C instead of 80C for the NdFeB)

Stainless Steel Belleville Disc Spring (mcmaster 9713K437) (6.6 degree inward angle) and jig to bore to correct ID
IMG_20151123_160242765_HDRa.jpg
New and old anode rings
SAM_4575a.jpg
SmCo magnet installed
SAM_4576a.jpg
Modified injector re-assembled
SAM_4578a.jpg
Ion beam
SAM_4581a.jpg
SAM_4584a.jpg
SAM_4582a.jpg
Video of operation
https://www.youtube.com/watch?v=DbfmR5t ... e=youtu.be
https://www.youtube.com/watch?v=UDQ1BAH ... e=youtu.be
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

Additional pole pieces have been tested to determine the effect of the magnetic field position on beam focusing
Numbers 1,2,and 3 from left, pole piece 1 was the one used in all previous tests
The version 1 has a 1/8" step of 0.5" dia, then a 1/16" step of 0.625" dia, then a 45degree taper over 1/16"
The version 2 has a1/16" step of 0.5" dia, then a 1/16" step of 0.58" dia, then a 15degree taper over 1/16"
The version 3 has a 1/16" step of 0.5" dia, then a 15degree taper over 0.1875"
SAM_4611a.jpg
SAM_4612a.jpg
Version 2 pole piece and plasma focus
SAM_4589a.jpg
SAM_4599a.jpg
Version 2 pole piece recessed and plasma focus
SAM_4606a.jpg
SAM_4609a.jpg
Version 3 pole piece and plasma focus
SAM_4621a.jpg
SAM_4622a.jpg
Version 3 pole piece recessed and plasma focus
SAM_4614a.jpg
SAM_4616a.jpg
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

Further pole pieces tested
Numbers 1,2,and 3 from left, pole piece 1 was the one used in all previous tests
The version 1 has a 1/8" step of 0.5" dia, then a 1/16" step of 0.625" dia, then a 45degree taper over 1/16"
The version 2 has a 1/16" step of 0.5" dia, then a 1/16" step of 0.58" dia, then a 15degree taper over 1/16"
The version 3 has a 1/16" step of 0.5" dia, then a 15degree taper over 0.1875"
The version 4 is 7.5mm long 14mm dia
The version 5 has a 1/16" step of 0.5" dia, then a 1/16" step of 0.58" dia, then a 15degree taper over 1/8"
Version 4 and 5 have a pump out groove milled in the base to vent the trapped volume inside the magnet
SAM_4651a.jpg
SAM_4652a.jpg
Version 4 pole piece and plasma focus
SAM_4653a.jpg
SAM_4659a.jpg
Version 5 pole piece and plasma focus
SAM_4660a.jpg
SAM_4662a.jpg
SAM_4663a.jpg
Version 5 is going to be the final version used to upgrade the ion sources, it seems to hold the best focus
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Re: Anode layer ion source. Operation pictures

Post by Steven Sesselmann »

Andrew,

Once again I commend you on your engineering skills and systematic approach to solving a problem, this work on your anode layer source would be worth writing a paper on.

It will be interesting to see if the narrower beam increases the fusion rate or efficiency.

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

Performance curves for the anode layer ion source
ALIS_curves.jpg
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

I finally got around to converting all the drawing for the ion source from my old cad program (KeyCad, made in 1992) into a modern program (Autodesk Inventor) and made some 3D models:
side.jpg
half-cut2.jpg
half-cut1.jpg
Anode-layer-ion-source-MF.jpg
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Re: Anode layer ion source. Operation pictures

Post by Werner Engel »

Did you allready try to focus the beam? Maybe with a Wehnelt cylinder or an einzellens?
Or is this even planned?
Higher luminosity would be nice - I think.
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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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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
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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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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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