Ion Gun Construction / Proposition

[pfostini]

I noted an effort by some members to combine the talents and knowledge of all of us to make a "superfusor". Problem: our membership is scattered all over the world! Since I constructed my fusor I have hit roadblocks in understanding some areas of ion guns and how to use them in a fusor.

Proposition - If we can somehow make these laser tubes work as ion guns, I am willing to send a free tube to each member that can help develope this idea. The cathode and tube will be in usable condition. Here are some details of the gun.

The cathode is from Semicon
http://www.semiconassociates.com/produc ... seril.html . The link provides details. The cathode is run AC at 10-20 amps. The Cathode legs are insulated from the cathode end metal shell. The opposite side of the ceramic which I will call the anode bell is seperated by the BeO ceramic that forms the bore. The Anode bell can be welded directly to a 2.75" conflat. Since the bore of the tube is much longer than a real IG I would guess the required voltage on the IG would be much higher than a traditional IG. The limitation is the ceramic can not be cut in any way. For cooling the ceramic, heat sinks can be clamped to the completed unit.

The cathode end has what I think all that is required to make that section work properly. The ultrator fitting provides the gas inlet. The anode bell may need some work. The anode bell - since it is welded to a conflat will be at the potential of the fusor shell. We need to pull ions out- correct? Extractor cone? voltage ? polarities, currents, insulated feedthrus? etc etc.These are some of the questions.

I have a lot of these tubes and could even put some effort into the manufature of what we require.

[LehighUBoy]

My suggestion is include a cylindrical electrode (negative bias) concentric with the channel in the insulator on the cathode end of metal shell using a high voltage feedthrough. Secondly, a magnetic field provided by a solenoid coil positioned in order to focus and constrict the ion beam. Just my initial thoughts …

-garrett

[Richard Hester]

Check the link to Heat Wave Labs (links section) for some interesting emitters/ion sources.

[3l]

I've been thinking about filamentless ion guns using an induction heater to make a anode glow.
Use a coated form and heat it to 1500 degrees....
red heat using electrical induction.
If you want to see one in a action goto:
http://www.powerlabs.org/index.html
Goto high voltage section.
Diagrams + pictures
Thanx to Sam Barrows for a really neat cheap way to go!

If you are cheap like me the heater could be as simple as a 10kv at 100ma neon xformer with a .01uf transmitting mica of the proper value and a small spark gap and a heating coil.
That's what my box of transmitter parts are headed to...making induction heaters. With no contact the induction heaters eliminate the isolation style of filament transformers ie..X-ray filament transformers which are rare as hen's teath and heavy as lead.
Safer to run with no electrical contact with the hot lead as in classical hot filament ion sources.

Had no idea such good quality electrodes would show up.
The BeO Tube would be usable in this mode.
I would be happy to work on a ion gun.... Those laser parts would be ideal for deuterium ion guns.
I've been trying to get the parts for six of them. (ion guns)

Fusion is fun!

Larry Leins
Fusion Tech

[pfostini]

Garrett; I made a quick drawing to move those ions along. That is do-able with the same feedthrus the cathode uses. They can withstand a few KV.

Larry; That is very interesting; Have you decided if you are going to use an ion emmiting source? Alkaline ?The cathode that is heated using RF would need to be inside the non-metalic area of the gun. I also have tubes that are more BeO for this type of operation. Would you be required to build 6 RF units or can you daisy chain the guns to one supply?

I would thing the cathode would be at some positive potential to hold electrons and repel the ions towards the grid. The neg bias electrode would help them on the way. The manetic field would confine the ions since thats what is used for confining the ions in an ion laser already.

[Starfire]

Phil, What is the cost of the tube? I would like to try to make a gun with this configuration. -What is the RF requirement, when used in the Ion laser ( freq. & Power ) also is it resonant in this application??

[pfostini]

I am willing to send them out at no cost ( sent your address via direct email to me) so we can try to make IG's with them. The tubes are ion laser tubes - they work off of an AC excited cathode and a DC arc down the bore. No RF . The wave guide CO2's work off of RF and require about 500 watts at 28 mhz and a very expensive power supply.
I have a lot of the tubes pictured and they have the IG basics.

In ion laser applications the cathode and tube withstand a DC arc of 15 amps and run thousands of hours. The cathodes I have been using in the fusor are these cathodes. I find I can run them at 11 amps AC to start emmision and they really stabilize the fusor at low pressures. As an IG they should withsatnd anything you throw at them and if exposed to air they can be re-activated. If we could come up with a common design we can then try different cathodes ( heatwave etc.) and build up some production units for us to play with at a very low cost. Actually the cost would be in the conflat or whatever way you would mount it to your fusor and any mods that we cant get off of the laser. I plan on calling my cathode suppliers and ask about Ion cathodes and pricing. Since I buy hundreds a year I should be able to get discounts. So if the ideas out there require a different cathode - its do-able.

[3l]

I was going the daisy chain them in a large supply
but many caps,spark gaps and coils. My original idea was to modify the duoplasmatron structure with a inductively heated neon sign electrode dipped in strontium , calcium carbonate and barium carbonate fired to leave strontium barium oxide and calcium oxide mix. A duoplasmatron works just like a flourescent bulb heated cathode and cold anode. The tube is surounded by a steel shell that goes down to a point.
The cold cathode is tungsten insert on the end of the steel point. The magnetic field confines the plasma to the tube away from the walls of the glass chamber tube and creates a plasma ball at the anode. An extraction electrode at 10 kv pulls ions from the plasma ball. It is the brightest source ( about 200 amps of ions for a modest unit ... commercial units can draw in the 2- 10 KA range) that an amateur could build without too much trouble or much machining. The only drawback is the original used tungsten filaments that get eroded away after a few hours of operation. thru sputtering . So in order to get 10,000 hours of operation, I thought a coated electrode heated externally would fill the bill.

Fusion is fun!
Larry Leins
Fusion Tech

[pfostini]

Are there any web links that would picture something close. I have not seen the inner working of a duoplasmatron device- only the outside of it. To produce the plasma ball wouldn't the gun have to be operated at a higher pressure than the fusor? Quartz tubing would withstand the RF on the electrode. Another idea- Since the cathodes I have are very heavy duty, could you somehow slide one into an electrode housing and still RF heat? The carbonates you mention are already in them.

[3l]

Hi Phil:
A diagram of the inside of a duoplasmatron is detailed in the following book.

"Building Scientific Apparatus", Moore, Davis and Coplan, 1989. A modern version of Strong's 1938 book on steroids. Into its eleventh printing!! Really superb. How to make ion guns!!!, etc. Complete and detail specs on NIM with simple interface circuits, IEE buss specs and much, much more...........
Several members of the forum have this book...may someone will post it.

Another gem is the Large Scale Generation of Ions....
As Soon as I get to the library I'LL get all the particulars.
the aurthor worked on the star wars ion weapons for the Pentagon and designed neutral d+ neutral generators in the 100,00 amp range for Tokamak Auxillary heating. Another book is the concise history of ion engineering and ion sources... Gold metal winners in the design of ion sources.

Fusion is Fun!
Larry Leins
Fusion Tech

[hellblazer]

This is such a great idea!

Here's some links to ion gun designs:

This is an excellent overview with internals to the duoplasmatron you wanted:
http://linac2.home.cern.ch/linac2/seminar/seminar.htm

This is another fairly good overview
http://www.casetechnology.com/source.html

For more indepth design, there's the online PDF books by Stanley Humphries (these books cost $300 in material form)

Charged Particle Beams http://www.fieldp.com/cpb/cpb.html

Principles of Charged Particle Acceleration
http://www.fieldp.com/cpa/cpa.html

[hellblazer]

The issue, as I understand things, is that once the ions get past the negative electrode, the electrode will become an ion decellerator unless there is something more to keep accellerating it. The inner grid of the fusor would be at a negative potential, so there would be accelleration due to that field. Hmmm... I'll have to see if I can model this and see if the ions have enough momentum to keep going down the tube long enough to be accellerated by the fusor cathode field.

(normal caveats - I've never done constructed an ion gun, so I'm likely making silly assumptions and mistakes)

[pfostini]

Some more results from our efforts. Nothing is permanent ( at least nothing a grinder can't handle). I will hold off on the conflat because I had to pay for that! The titanium electrode was from CO2 laser fabrication.

[Starfire]

An amateur radio rig on 10 meters will certainly provide the 28Mhz @ 500 watts ( and KW's depending on the rig and linear amp ) it would only be a matter of matching the out-put. If that is required.

[3l]

Very nice Phil!

The ion gun can get pretty hairy on cost due to the material issues of refractory metals and the shapes ect. You have done a great job of adapting the existing tech to a useful form for fusor work. Cudos. The device you built will work nicely without rf excitation. We should run it without excitation first to work out any unsuspected bugs. As the designs progress then raise the power. I would say 15 amps would be a good starting point. Beam focus and optics might be
an area that will chew up some time but things are moving along nicely. Low power will allow you to use a sheet of quartz to see how the focus of your optics is going. I would say build the first generation without Rf
to see how it goes then Use RF in the updated version.

Fusion is fun!
Larry Leins
Fusion Tech

[LehighUBoy]

Phil Fostini wrote:
> Some more results from our efforts. Nothing is permanent ( at least nothing a grinder can't handle). I will hold off on the conflat because I had to pay for that! The titanium electrode was from CO2 laser fabrication.

My only suggestion is optimize the accelerating cylinder lengths, specifically maximize the distance between the filament and first negative potential. If possible surround the vacuum side lead with ceramic type insulator in order to minimize field distortions. Electrical comments are ground both metal shells and provide a positive potential to the filament (as you mentioned before). In general, your initial modifications look good, specifically designing one end to allow the solenoid to slide over the device!

-garrett

[pfostini]

The cathode side electrode at the moment has its far end up against the BeO bore. Would it be OK to maximize the distance by making it shorter? Cut it in half and push it as far away from the cathode as I can?
I will look around and see what I have for ceramic insulation, I have also quartze tubing that may work.

[pfostini]

Quartz we have plenty of also. That sounds like a stratagy. Is 15 amps the cathode current or accelerator current DC. I could start scrounging for power supply materials.

[LehighUBoy]

Phil Fostini wrote:
> The cathode side electrode at the moment has its far end up against the BeO bore. Would it be OK to maximize the distance by making it shorter? Cut it in half and push it as far away from the cathode as I can?

Attempt to segment the cathode side electrode into fourths and place one section at a maximum distance from the filament. The insulation arrangement is diagramed in the attached image (I apologize for the crude nature of the drawing).

-garrett

[pfostini]

> Attempt to segment the cathode side electrode into fourths and place one section at a maximum distance from the filament.

Segment the 1" Ti electrode into .250 and take `one of the .250" pieces and place it where you show it , correct? I will need to find a way to cut the Ti, I also have stainless if that can withstand the temperatures. But if Ti is better overall I would prefer we make units with a good lifetime. The cathode end when completed would be welded back onto the bore and we do not want to go in there too much. I get away with cutting the weld two more times after this one. The cathode have a rated life of several thousand hours.

It would not be any problem to do the insulator as shown. If I have enough ceramic that we can all share then I will use that but if not we will use quartz tubing.

Hey your drawings are better than my scanned in hand sketches.

[pfostini]

I do have plenty of Ham gear around (N1RDT) and a Lepel 1.5KW. My wife and I loaded an Xray transformer into a plastic tube and I am getting ready to "float" it in oil. They are not light.

[LehighUBoy]

Phil Fostini wrote:
> > Attempt to segment the cathode side electrode into fourths and place one section at a maximum distance from the filament.
>
> Segment the 1" Ti electrode into .250 and take one of the .250" pieces and place it where you show it , correct?

correct

[Richard Hull]

You guys seem to be going for the jugular!! 15-30 amp filaments! Refractory materials!?

I would have thought a superb, yet simple, ion gun might be constructed first based on the basics outlined in " making scientific instruments". A simple 1 or 2 amp coated filament dispenser cathode operating at very low temps, light duty 200 volt acceleration with coaxial magnetic field should do the trick for test purposes and let mistakes be made cheaply.

I do know for a fact that the ion guns on the Farnsworth device had to be differentially pumped (read vacuum nightmare to the un-annointed).

The ion guns being discussed here sound rather overkill for a trial. Mistakes can bore a hole in a fusor shell in seconds. The Farnsworth team did it all the time with much more puney guns.

Were it me doing this, I would go for two ultra simple guns ONLY and coaxially align and operate them to "fire for effect" before moving forward. Along the way I would modify the guns to suit the effort and better my gun design techniques before making up a phalnax of them in a most super machine. Once I obtained all I could from a low powered, six gunned simple machine, only then would I go for a monster gunned system.

Still, I applaud the effort and hope all works out well.

Richard Hull

[guest]

Sound advice Richard, but there is much to be learnt with Ion guns. If a stable device can be produced will this not facillate a more controlled fusion and allow a better measurement inviroment? The comment of "fire for effect " is taken onboard - I seek a device which is prolific in production of Ions and yet can be responsive to fine adjustment and control.

[pfostini]

If we can make these tubes produce the ions then the cost is only in the mating flange to the fusor.