Triple grid design at LANL

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
davidtrimmell
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Triple grid design at LANL

Post by davidtrimmell » Tue Feb 17, 2004 6:18 am

Is anyone here familiar with the method that Mark Pickrell at LANL has worked with? I believe the outermost grid is at +200V with the second at ground potential and the innermost at -100KV.

They claim to have actually done 10^10/sec.

I quote from:

"Novel Methods for Neutron-Induced-Gamma Detection of Land Mines and Buried Explosives"

"...Using internal funds, extensive plasma physics simulations have been run at LANL to explore
methods to increase the neutron yield. Using a fully kinetic, 1.5 dimension plasma code with full atomic physics, we
have developed an IEC design that can produce 1011 n/s. The underlying physics principals are straight-forward. In
order to increase the neutron yield, the density must be lowered below the Paschen breakdown limit. This operation
can be achieved using a novel triple-grid design. (Conventional IEC systems use only a single grid). The triple-grid
system decouples the plasma breakdown from the ion acceleration, thus obviating the Paschen limit...."

Mark M. Pickrell, NIS-5, MS E540, Los Alamos National Lab
http://www.uxocoe.brtrc.com/TechnicalReps/SD52.pdf

David Trimmell

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Brian McDermott
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Re: Triple grid design at LANL

Post by Brian McDermott » Tue Feb 17, 2004 1:11 pm

They are using the D-T reaction, which explains the higher neutron yields. The cross section for that reaction is usually higher that that of D-D for a given voltage.

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Re: Triple grid design at LANL

Post by 3l » Tue Feb 17, 2004 1:43 pm

Hi guys:

You may not realize this but Joe Zambelli of this forum did a tripple grid a few years ago and got good results.
You don't need computer code to tell you that you get better results at higher vacuum....better mean free path...faster the ions.
Pulse fusion in d-d easily surpasses 10^11 neutron on a 5 GW pulse "below the Paschen limit...{<1 millitor}". No special gas mixture needed. Heck IF we could run pure T-T the IEC would already be past breakthrough. But that is dreaming! The goverment will never allow a commercial process with the stuff ever. It is in too short a supply and crucial to defense.

Happy Fusoring!
Larry Leins
Fusor Tech

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Richard Hull
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Re: Triple grid design at LANL

Post by Richard Hull » Tue Feb 17, 2004 6:45 pm

Brian is correct. The D-T was the catch here. D-T mixture is good for a 10e3 expansion of a common fusor. As Jon Rosentiel has tickled 10e7 with his D-D fusor, give him some D-T and he would be at 10e10n/sec. So the LANL fusor is no great shake.

They have just effectively lowered the pressure allowing for a more complete recirculation of ions and hung in a couple of extra grids to get about a 5x or 10X improvement over the common fusor. Laudable, but a more complex operation with NRC licensable reactants.

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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Re: Triple grid design at LANL

Post by davidtrimmell » Tue Feb 17, 2004 7:02 pm

So, there is no way (as of yet) to do 10^10 Neutrons/sec. without NRC licensed material? I would be curious as to what people think the amateur community will be able to reach? What might be the absolute limit with D-D considering a less then Corp. or Gov. budget?

David Trimmell

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Richard Hull
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Re: Triple grid design at LANL

Post by Richard Hull » Tue Feb 17, 2004 8:01 pm

With current designs and up to say 150,000 volts applied I would think 10e8 or even 10e9 would be possible. This would include pulsed systems averaged rates.

Pulsed systems might blast out many more neutrons per pulse, but the time ordered average would be no more than a CW fusor. This is at amateur levels, of course.

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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Adam Szendrey
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Re: Triple grid design at LANL

Post by Adam Szendrey » Tue Feb 17, 2004 8:22 pm

Well, this is just another crazy idea...but i think a cylindrical grid could be made into a coil (flat or standing;essentially it would look like a tube coil but the tube in this case is transparent to the ions), resulting in a long spiral plasma string. Well? What do you think? (essentially it's like several donut grids placed ontop (standing coil) of eachother but the plasma string is not broken (several rings) but a continous spiral)

Adam

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Carl Willis
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Re: Triple grid design at LANL

Post by Carl Willis » Tue Feb 17, 2004 8:50 pm

Adam,

The cylindrical geometry has been used before, I think most notably by a group led by K. N. Leung at LBL to produce a D-T source that I think has reached 10^14 n / s. [Look for his website for the lit. references, I cannot remember the details right now].

It has a number of advantages just due to the simplicity of the layout. For example, external magnets for improving ionization by electrons would be easier to implement; the cathode structure itself would be perhaps easier to fabricate, and there are other advantages regarding the construction.

A practical disadvantage is that you may need to support the cathode with a standoff at both its ends.

Someone should consider that geometry for their next fusor as an experiment. My second fusor, still in the works, is a 6" chamber with standard spherical cathode (I already have some made, that's why).

-Carl
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Carl Willis
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Re: Triple grid design at LANL

Post by Carl Willis » Tue Feb 17, 2004 9:00 pm

Well, regarding my just-previous post, I'm mistaken in thinking that Leung's designs are of the IEC type. Nevertheless, they are interesting and some, especially the spherical design at the bottom of the page cited, have a lot of similarity to the Fusor.

Dr. Leung apparently produces ions in these sources with inductively-coupled RF discharges.

And, he's estimating over 10^12 n / sec D-D for some of the designs.

Here's the link:
http://www.lbl.gov/Tech-Transfer/techs/lbnl1764.html

-Carl
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Re: Triple grid design at LANL

Post by 3l » Tue Feb 17, 2004 10:55 pm

Hi Carl:

Been there done that!
That was my first demo machine.
A helix diped into creamic clay bisque and fired makes an excellent electrode for RF excitation.

Happy Fusoring!
Larry Leins
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