Starfire Ion Gun Test

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Steven Sesselmann
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Starfire Ion Gun Test

Post by Steven Sesselmann » Thu Mar 06, 2008 3:49 am

Hi Guys,

Short test of the Sesselmann/Hendron Starfire Ion gun on youtube.

http://www.youtube.com/watch?v=7B1TLdsS1pY

TECHNICAL:
Ion gun mounted on the S.T.A.R. reactor
Vacuum is around 1 micron
Zero voltage on the S.T.A.R. cathode
Filament heater adjusted from 0 to 6 volts
Bias voltage with cold filament -1000V
Bias voltage at max current -300V
Max current 100 ma.

Have fun..

Steven

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http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

John Futter
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Re: Starfire Ion Gun Test

Post by John Futter » Thu Mar 06, 2008 6:25 am

When you get your HV PSU back a few experiments to find the actual ion current - neutrals would be in order.

You probably will need secondary electron suppression to get a real figure.

This will require an aperture just before the grid biased 200 to 600 vots away from your grid to suppress the the secondary electrons.


Typically @ work with a 1 mA beam, target current (Grid in your case) is 1mA but with secondary electron suppression current drops to between half to threequarters of the ion gun gun current showing total ionised ions the rest of the current is actives killing themselves within the ion source. In the implanters and the ion beam deposition chambers we have found agreement of integrated ion charge secondary electron suppressed implantations / films with RBS NRA and (PIXE for impurites from the ion guns / steering focusing elecrodes).
ie total implanted ions by measurement equals the integrated charge collected from the target.

some more eperiments could be in order

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Mike Beauford
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Re: Starfire Ion Gun Test

Post by Mike Beauford » Thu Mar 06, 2008 6:28 am

Nice work Steven. Look forward to seeing it in action with test results in your S.T.A.R. unit.
Mike Beauford

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Steven Sesselmann
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Re: Starfire Ion Gun Test

Post by Steven Sesselmann » Thu Mar 06, 2008 10:28 pm

First Mike,

Thanks for your unchanging faith in S.T.A.R., I will do my best not to let you down

John,

Experiments to measure the current of the Starfire Ion gun is definitely on the agenda.

You may need to explain to me, what you mean by supression of seconday electrons. If I understand you correctly, these are the electrons that get knocked off the atoms when the ions are created, but I can't understand how they could make it anywhere near the cathode, when the cathode has a strong negative charge.

The Starfire ion gun strips the electron off the deuteron as the gas passes through it, and all the free electrons are all collected in the muzzle.

My understanding is that the ion beam current will be the current drawn by the main PSU, especially since the S.T.A.R. reactor does not emit electrons from the cathode.

I need a translation for:

RBS, NRA, PIXE

PS: We could do with a little link to a page with a dictionary to these acronyms.

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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Richard Hull
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Re: Starfire Ion Gun Test

Post by Richard Hull » Fri Mar 07, 2008 3:28 pm

Wrongo Steven.........

Ion guns are gross energy sinks!

An ion gun that utilizes a kilowatt off its ionizer supply and drags 500ma of current out of a 2kv input might supply a Deutron beam of 1-2 ma.

10 ma of ion current is considered a very intense ion beam.

Most simple ion guns supply in the 100's of microamps of beam current.

One thing can be said of ion guns............They do not like to make ions and put them out into a beam..... The net result of an ion gun supply is a lot of ionization-recombiantion that ends up as heat and a very tiny amount of the supplied energy actually spurting out the extractor as ions.

Really massive 10-50 kw ion guns can supply 100 ma or more. These are very rare outside of special nuclear research apps.

For basic amateur use it is going to be tough to beat the pigatron. The earliest posts here give some info on the pigatron.

viewtopic.php?f=12&t=4941#p32249

Ion guns are traditionally used only in differentially pumped systems. (guns at high pressure and the chamber they spit into at a significantly reduced pressure, (3-6 orders of magnitude difference.)


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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Steven Sesselmann
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Re: Starfire Ion Gun Test

Post by Steven Sesselmann » Fri Mar 07, 2008 8:57 pm

Richard,

I think my previous post was unclear, I was not suggesting that the ion beam would equal the power drawn by the ion gun, which as you correctly state is in the 100's of watt.

I was referring to the current drawn by the main PSU of the fusor. In the STAR reactor we set up a potential difference between the hollow cathode and the ion gun, which is at ground potential, and because the cathode in my reactor does not act as an electron emitter, we can assume that the current drawn, is due to positive ions transferring their charges to the cathode.

So we simply read the milliamps off the PSU meter and convert to current.

This is be best tested at very low pressures, as the plasma will become conductive at a point, and allow an electron current to stream from the cathode back up the tubes.

Details of the Starfire Ion Gun patent should be published within the next 30-60 days, and we look forward to discussing the devise in more details then.


Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
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Re: Starfire Ion Gun Test

Post by Starfire » Sat Mar 08, 2008 2:03 pm

I might add, that the Starfire Ion Gun is based upon principles outlined by Richard Hull in an earlier post - in that it uses ceramic structure for high heat handling

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Carl Willis
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Re: Starfire Ion Gun Test

Post by Carl Willis » Sat Mar 08, 2008 5:03 pm

Hi Steven,

Secondary electrons are a common problem in charged-particle beam measurements. Usually to make these measurements on a continuous beam, some sort of collector (e.g. a Faraday cup) are placed in the beam and the current to that conductor is measured. Secondary electrons are emitted when a beam strikes the material, however. These electrons leaving your collector constitute a current that adds to the current due to beam ions and ruins the measurement unless the secondary electrons are suppressed with an electric field that returns them whence they came. Measuring twice or three times the beam current you actually have is quite frequent if secondaries are not suppressed.

-Carl
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Steven Sesselmann
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Re: Starfire Ion Gun Test

Post by Steven Sesselmann » Sat Mar 08, 2008 9:57 pm

Carl,

Thanks for explaining what John F. meant by secondary. I have heard of this phenomenon before, it is the impact of ions on the hard surface that knocks electrons out, similar to the photoelectric effect.

This would be applicable if you are shooting a beam of ions onto a flat surface target.

However, inside the star reactor hollow cathode, electrons have nowhere to go, except back to the cathode on the opposite side, it is itself a Faraday cage.

For this reason, I believe that the current measured between the ion gun and the cathode, will be very close to the actual ion beam current, providing the plasma is diffuse enough, not to act as an electron conductor.

We instantly see when the plasma becomes conductive, voltage falls off completely and current goes off the scale and the PSU fuse trips, so our measurements need to be done below this threshold.

Thanks Carl, I learned another thing today..

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: Starfire Ion Gun Test

Post by inflector » Tue Sep 16, 2008 3:29 pm

Richard Hull wrote:
> Ion guns are gross energy sinks!
Is this really any different than what happens in the center of the fusor when the ionization is done there? Isn't there a big energy drain caused by the ionization itself in the core?

I have been thinking about the net energy equation with fusors and it seems to me that the heat losses could be recovered in the event we got a design where continued operation was feasible. This would change the input/output equation considerably even for the currently running fusors if we consider heat a desirable output rather than a waste.

I realize that current designs die because of excess heat but I think we can eventually come up with a cooled inner grid version that uses ion guns for ion generation. Presumably, heat is eventually what we want out of a fusion reactor if we consider a first-generation net-power model (i.e. before going to direct electric conversion). Even if we get to a direct-electricity neutronless fusion reaction like p-B11 there is still going to be heat from some of the alphas striking something other than the electrical collection grid.

> Ion guns are traditionally used only in differentially pumped systems. (guns at high pressure and the chamber they spit into at a significantly reduced pressure, (3-6 orders of magnitude difference.)
Is this done to provide ion flow? Is the electrostatic charge differential not enough in that case? I guess I'm asking why the differential is important?

Thanks in advance,

Curtis

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