Anode layer ion source. Operation pictures

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Jon Rosenstiel
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Re: Anode layer ion source. Operation pictures (Feedthrough flange, 30min operation, temperature data)

Post by Jon Rosenstiel »

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

Post by Andrew Seltzman »

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

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Final Design Modifications. Faraday Cup Measurements

Post by Andrew Seltzman »

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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Steven Sesselmann
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Re: Final Design Modifications. Faraday Cup Measurements

Post by Steven Sesselmann »

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

Post by Andrew Seltzman »

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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Steven Sesselmann
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Re: Final Design Modifications. Faraday Cup Measurements

Post by Steven Sesselmann »

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

Post by Chris Bradley »

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

Post by Carl Willis »

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

Post by Steven Sesselmann »

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

Post by Andrew Seltzman »

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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Anode layer ion source. Set of 5 complete and tested

Post by Andrew Seltzman »

All 5 ion sources have been completed and tested to produce an ion beam for 30min continuously. All 5 have been helium leak checked to the 10^-8 range, initialy 2 of the welds were bad, however those have been repaired.

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Richard Hull
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Re: Anode layer ion source. Set of 5 complete and tested

Post by Richard Hull »

Needless to say, we are all looking forward to the final operation and reports related to all this hard work you are doing. I wish you all the very best in this first effort at a fully gunned amateur fusor..

Richard Hull
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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. Set of 5 complete and tested

Post by Dustinit »

I also am looking forward to seeing this in operation.
Fantastic effort andrew.
As a possible extension on the idea,
I view the design as an assymetric penning trap which traps electrons
and pushes out the ions.
Therefore I see no reason why it needs to be a circular source,
So if you used bar magnets instead, interspaced with electrodes it may be possible
to build a source around the circumference of the fusor, or possibly all the fusor wall space if magnets are placed in a grid pattern.
This would make a more uniform source but I'm unsure it would have any benefits over Andrews superb effort.
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Re: Anode layer ion source. Set of 5 complete and tested

Post by Steven Sesselmann »

Dustin,

A few more good lateral ideas there, good one!

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Re: Anode layer ion source. 4 mounted on core

Post by Andrew Seltzman »

4 ion sources are now mounted on the core.

In this picture 1 of the ion sources is in use at about 800v on the source anode and about -2kv on the grid. The plasma will form a stable discharge all the way down to very low voltage on the grid with no observable pulsing or flickering even with 0.5mA collected by the grid.

When all 4 sources are put into operation, they should allow very stable operation at high vacuums and low grid currents.

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Re: Anode layer ion source. 4 mounted on core

Post by Steven Sesselmann »

Andrew,

Nice work, excellent photo, I can see your ion source working at the back of the chamber.

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Re: Anode layer ion source. 4 mounted on core

Post by Carl Willis »

Hi Andrew,

Looks like steady progress that is likely to pay dividends in the neutron department. This is an advanced development for sure. Good luck getting your high vacuum back in business, and I hope you can find the gas pressure "happy medium" between operability of the ion sources and desirable characteristics in the main discharge.

-Carl
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Re: Anode layer ion source. Operation pictures

Post by Andrew Seltzman »

Well, it's been 5 years since I last posted in this thread, but the quad ion gun setup for the Mark 3 fusor is now operational. Pictures of the power supply and setup follow:

Ion injector operating in testbed
SAM_3242a.jpg
Ion injector operating in testbed
SAM_3244a.jpg
Control board, 4 adjustable buck converters for EMCO HV power supplies
SAM_3240a.jpg
EMCO HV power supplies (5kV, 3mA), box and front panel
SAM_3241a.jpg
Power supply assembled
SAM_3266a.jpg
MHV connections to the 4 anode layer ion sources on the fusor
SAM_3267a.jpg
Star mode with 4 injectors running at 700v anode bias
SAM_3253a.jpg
The supply will be further upgraded to have a fiber optic signal to allow the injectors to be pulsed. This is so a capacitor can be placed in parallel with the central grid and charged up while the fusor is pumped down below the minimum paschen breakdown pressure. The injectors can then be pulsed triggering the breakdown and generating a very high density plasma for a short period of time (for use with the laser density probe).
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Re: Anode layer ion source. Operation pictures

Post by Richard Hull »

Any fusion, neutron numers on this most interesting setup?

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Re: Anode layer ion source. Operation pictures

Post by Dennis P Brown »

Very professional setup - your design and execution appears to be working extremely well. Hope this provides far better fusion results!
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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,
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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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