Fusor Forums

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.

Andrew Seltzman
www.rtftechnologies.org

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

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.
Dustin

Dustin,

A few more good lateral ideas there, good one!

Steven

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.

Andrew Seltzman
www.rtftechnologies.org

Andrew,

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

Steven

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

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 Ion injector operating in testbed Control board, 4 adjustable buck converters for EMCO HV power supplies EMCO HV power supplies (5kV, 3mA), box and front panel Power supply assembled MHV connections to the 4 anode layer ion sources on the fusor Star mode with 4 injectors running at 700v anode bias 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).

Any fusion, neutron numers on this most interesting setup?

Richard Hull

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

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

Hi Werner,

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

Andrew

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

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 New and old anode rings SmCo magnet installed Modified injector re-assembled Ion beam Video of operation
https://www.youtube.com/watch?v=DbfmR5t ... e=youtu.be
https://www.youtube.com/watch?v=UDQ1BAH ... e=youtu.be

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" Version 2 pole piece and plasma focus Version 2 pole piece recessed and plasma focus Version 3 pole piece and plasma focus Version 3 pole piece recessed and plasma focus

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
Version 4 pole piece and plasma focus Version 5 pole piece and plasma focus Version 5 is going to be the final version used to upgrade the ion sources, it seems to hold the best focus

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

Performance curves for the anode layer ion source

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:

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.

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).

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 A high speed camera was used to observe the plasma discharge. These are from ~3ms long discharges
at 420fps at 1000fps 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) 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?

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

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 Ion source with new anode design Ion source with new anode design Batch of 6 new ion sources using the new design

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?