Hirsch versus Farnsworth

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Hirsch versus Farnsworth

Post by guest » Sat Aug 02, 2003 4:38 pm

For many years I have read the posts on this board and I have to disagree with one assumption that has been perpetuated and reinforced on the board, and that is that the Hirsch's approach to IEC fusion is a superior approach for achieving IEC fusion.

Hirsch approach is what we normally call the Fusor, which makes the outer shell the anode and the inner grid the cathode. This inherently results in ions being accelerated towards the grid while electrons are continuously fed into the system through the cathode grid.

The approach does results in higher fusion reactions in the short term, but the demand for power (Watts input) rises exponentially.

I have no doubt that Farnsworth approach was more along the lines of what Dr. Bussard has been attempting to do, because his approach seem to concentrate on trapping electrons which in theory would coax the ions to be attracted and trapped within the virtual cathode.

The Farnsworth approach obviously does not work in a purely electrostatic system, however if it did, it would make for a more electrically efficient IEC device than the Hirsch approach and that would increase the chances at breaking even.

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Adam Szendrey
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Re: Hirsch versus Farnsworth

Post by Adam Szendrey » Sat Aug 02, 2003 8:17 pm

Hi Nathan!

Well in my oppinion (which changed since i have joined this forum) the fusor in its current state and form is nothing more than a proof, a start. A proof that fusion "is easy" . No multi billion dollar device is needed to achieve it. A demonstration of a very ingenious idea. A fusing fusor is a nice neutron /x-ray/fast ion source. Also some very interesting experiments can be done with it, different fuel mixtures can be tried. And something to really look at too, something to be proud of. I would guess that a practical fusion power source will be a whole (okay not THAT much) different thing, using the same principles. Maybe it will be a pulsed system , maybe a resonant type, maybe a resonant-pulsed system... I think it will not be a simple DC design. The grid structure, or even the method of colliding ions might (probably) change too. The simple fusor design could become a sub-luminal propulsion method in space. There is a long road to go right? I'm looking forward to it.

Adam

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Re: Hirsch versus Farnsworth

Post by Carl Willis » Sun Aug 03, 2003 2:20 am

Hi Nathan,

Are you suggesting that more fusion might result for a given power level if the grid is made positive?

I don't recall if anyone here with a neutron-producing fusor has ever reversed their power supply just to see how many counts they get with a positive inner grid. I'm betting there would be some counts (due to deuterons accelerating radially outward and colliding with neutral gas), but I cannot imagine getting the high electronic space charge in the center to make that mode of operation very successful.

Why wouldn't a "purely electrostatic" system be appropriate?

-Carl
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Re: Hirsch versus Farnsworth

Post by guest » Sun Aug 03, 2003 5:03 pm

Hi Carl, if you look at Farnsworth patent 3,258,402 you will see the arrangement we use today for making fusor’s was patented by Farnsworth prior to Hirsch joining the team, however the inner grid was the anode and the outer shell was the cathode while an intermediate grid was a control grid.

Another way to summarize the difference between the Farnsworth approach and the Hirsch approach is to say that Farnsworth was making an electron tube that would coax ions to be confined within a virtual cathode, while Hirsch was working on an ion tube that would coax ions to be confine at the center, but gave little or no concern to a virtual cathode.

The difference is that Farnsworth recognized the absolute need for a virtual cathode as the primary ion confinement system, while Hirsch took advantage of the much higher initial fusion reaction rate that can be achieved via the primary acceleration and confinement of the ions.

If you subsequently look at patent 3,386,883 you will see that by this point Farnsworth was using an inner cathode, however it was not a grid, but a sphere with electrostatic lenses made of tungsten, which would confine the ions within the sphere as they were injected through the lenses via ion guns.

Farnsworth version of the arrangement is easy to recognize, because they are the kind that have the inner side of the spherical cathode, coated with Beryllium copper.

What’s the benefit of Beryllium copper? It is a known secondary electron emitter. The only reason you would do this, is because you are trying to initiate a secondary electron emission cascade, also known as multipacting.

This is not a trivial fact, instead look at where Farnsworth himself says he came up with the idea for the IEC concept and you will find that it was his observation of glowing spheres in his multipactor amplifiers that were the inspiration for his idea of the IEC, this is another fact.

Farnsworth once again was concentrating on the virtual cathode while Hirsch just wanted to drive ion currents directly.

Today the Farnsworth approach might be worth trying again in light of the fact that the Hirsch approach has reached its practical limitation. The coaxing of the virtual cathode through multipacting can be greatly increased today in a spherical cathode inner surface through the use of a carbonized diamond layer which is known to produce in excess of 1000 electrons emissions per electron or ion strike, this when compared with Beryllium copper which has a known secondary electron emission rate of less then 10 electrons per strike, this of course varies with strike energy, voltage, etc.

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Re: Hirsch versus Farnsworth

Post by guest » Sun Aug 03, 2003 5:44 pm

Just what is a <b>carbonized diamond layer </b>? I just have the feeling that the virtual cathode is the way to go for fusion. The reasion I ask just what the diamond layer is because industral diamonds are dirt cheap.

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Re: Hirsch versus Farnsworth

Post by Adam Szendrey » Sun Aug 03, 2003 5:59 pm

I am in the process of translating a text from hungarian to english from a book. There some of what you say is written Nathan, for example that Farnsworth noticed small bright glowing "dots" in the center of his multipactor tubes, and that the way they went finally was a RESONANT approach, using a modulated power source, periodically "squeezing" the confined plasma in a resonant manner. At one period the electrons were in the center (virtual cathode) attrackting the positive ions , in the other period the ions are in the center etc.

Adam

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Re: Hirsch versus Farnsworth

Post by guest » Sun Aug 03, 2003 6:06 pm

The carbonized diamond is actually an old term; today everyone calls it diamond deposition or diamond coating. The main process is called Chemical Vapor Deposition (CVD) and it can either deposit a layer of diamond onto another surface or even create a thin freestanding structure.

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Re: Hirsch versus Farnsworth

Post by Carl Willis » Sun Aug 03, 2003 6:46 pm

Does someone here have a neutron producing fusor, who wouldn't mind trying a positive grid just for the hell of it? Jon Rosenstiel? (I know yours is a pretty hot neutron producer). For my setup this would have been as simple as plugging the HV cable into the anode socket rather than cathode socket on the x-ray machine. And it sounds like a very worthwhile experiment.

I have a summer internship at a company developing proton linacs. Lampblack coatings (carbon) have been used here for the express purpose of SUPPRESSING secondary emission, which exacerbates unwanted electron multipactoring between drift-tube stems and robs the system of a great deal of power. Carbon has LOW secondary electron yields, insofar as my experience tells me. What is it about a carbonized CVD diamond film that makes it so much different?


-Carl
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Re: Hirsch versus Farnsworth

Post by guest » Sun Aug 03, 2003 7:08 pm

Found this at,
http://www.grc.nasa.gov/WWW/RT1998/5000 ... insky.html

"Diamond is a promising semiconductor material for novel electronic applications because of its chemical stability and inertness, heat conduction properties, and so-called negative electron affinity (NEA). When a surface has NEA, electrons generated inside the bulk of the material are able to come out into the vacuum without any potential barrier (work function). Such a material would have an extremely high secondary electron emission coefficient s, very high photoelectron (quantum) yield, and would probably be an efficient field emitter.

Chemical-vapor-deposited (CVD) polycrystalline diamond films have even more advantages than diamond single crystals. Their fabrication is relatively easy and inexpensive, and they can be grown with high levels of doping--consequently, they can have relatively high conductivity. Because of these properties, diamond can be used for cold cathodes and photocathodes in high-power electronics and in high-frequency and high-temperature semiconductor devices".

The only practical way I can think of at this moment to do (CVD) would be to send a component out to someone who already does that kind of work.

While probably not super expensive it’s probably outside of most of our budgets.

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Re: Hirsch versus Farnsworth

Post by Carl Willis » Mon Aug 04, 2003 3:57 am

That's a rather neat thing to know about diamond! Never would have suspected that it has high secondary electron emission. BUT I think it must be doped in order to do that. Pure diamond has a ~3eV bandgap and makes a fine insulator. Without at least 3 eV / electron, there would be no emission from a pure diamond.

One could potentially make awesome field-emission cathodes and obviate the need for thermionic electron sources, in CRTs, other vacuum tubes, electron microscopes, fusors, etc etc. They'd probably be reasonably cheap, too.

Cool!

-Carl
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