z-pinch instabilities

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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grrr6
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z-pinch instabilities

Post by grrr6 »

I was wondering about z-pinches. I wish i could find more research papers, but i can't find a darn thing besides stuff about how good snadia is:P Hal, how do you find all those lovely electronic articles?
Anyways, i was wondering about what the Raleigh-taylor instability was, and how they are trying to get around it.
hellblazer
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Re: z-pinch instabilities

Post by hellblazer »

From scouring the net. I seem to have a knack for it, as even here at work, I can find stuff in about 5 minutes that co-workers have been looking around for days. Strange.

Anyways, there's the IOP Electronic Journals home http://www.iop.org/. Lot's of stuff online and searchable. Unfortunately, you have to pay for the download for most stuff - some is free.
3l
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Re: z-pinch instabilities

Post by 3l »

Z-pinches date from the 1960's.
Mather did the work in the US.
Sorry kids the work is just in books.
No internet when the work was done.
The instability you seek is what happens when the the fusor ball is out of wack. The other name for it is the flute instability..... ions are lost at the sides of the fusion site as the cluster of ions vainly oscillate to achieve stability. A good plasma ball will be 10 microns across and will be a tight knit bundle of fusion for as a couple of microseconds. It breaks up by the instability a microsecond later. The IEEE magazine once covered all this stuff in 1976.

Drawbacks...
It takes a boatload of juice to make it fly. Scale up is a very large undertaking... the breakeven is in the mega joule range. However as a test source for neutrons you can get by with 200 joules and get 1x10^6 neutrons. Limited duration. Limited voltage but exponential amperage. A 1200kj Focus will give 10^18 neutrons but it takes a million dollars worth of caps to do it. Change the fuel mix to dt and you can get 10^21 neutrons. It has never been a practical power source.

Advantages....
runs at 10 torr on plain old deutrium.
Simple geometry.
Xrays in great profusion.
Can run advanced fuels.... but I think it's just a theory...
never tried out in real life.
Output can be boosted by putting a trace of Argon in the deuterium gas .

The belljar has a do it yourself Dense Plasma Focus device.
http://www.belljar.net/ in:
Neutrons and Neutron Generators
At the tail end are all the books and patents to look at
in the cited references
At the very end is a great book on the subject.
I wore out the school's (Ole Miss) copy reading it.
Before I got my fusor stuff rolling I considered building one as a neutron test source.
I simply took the power switching designs and applied the usefull ones to my pulsed fusor project.
But the fusor gets the same number of neutrons with less stress and a lot fewer joules per neutron delivered.

Larry Leins
Fusion Tech
grrr6
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Re: z-pinch instabilities

Post by grrr6 »

10^21 with DT, thats past break even at 1.2 MJ delivered, where did you see a figure like that?
10^21 neut x 14 MeV/deut x 1.6E-19 J/eV = 2.2 GJ Thats somewhat more than 1.2 MJ I'd say ;)

Turns out i have heard of it before, as the sausage instability. When the plasma column contracts, the contraction is promoted by the incrased magnetic fields, so that it contracts more, and can even stop the current flow - something i didn't know. I would think that a smaller column would be better, as density there should increase, but i guess if it blows itself out, then its no good.
The kink instability is something else, that i knew of, and i think i have a way of combatting that, dont know if itll work yet though, so i gotta think it through further.
LehighUBoy
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Re: z-pinch instabilities

Post by LehighUBoy »

The majority of MHD instabilities are handled with E x B drift. I've found some cleaver ways to induce this mode with microwaves, though fairly complicated and expensive. My torsatron page summarizes my research (I apologize for referencing this device fairly frequently, however I learned a tremendous amount from experimentation with the device in high school)

-garrett
3l
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Re: z-pinch instabilities

Post by 3l »

They ran a z-pinch device at Los Alamos, Sandia, and LLNL They had a 1.5 meter in diameter unit for their z-pinch work. That unit achieved a neutron number at 10^21 neutrons but the cost was about a magnitude higher than a small reactor system of the same yield.
Worst yet it took about 30 Gw delivered power due to losses in application of that power.
The other problems was the power conversion was complicated by the copious xray output but little heat.
It was dismantled and turned into the Hermes system then into the Zeuss linear Z-pinch device. The remaining work in this field is now at Sandia with a colossal new z-pinch device. I posted on this device
in Fusion History & News Forum under:.
2001-12-17 08:58 The z pinch machine (3l) [Latest: ] (5)

Larry Leins
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grrr6
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Re: z-pinch instabilities

Post by grrr6 »

Now i see why you were going for DPF research. It turns out that instabilities in a DPF take 700 times as long as they would in a normal z-pinch, becuase of the sheared flow around the pinch resulting from the initial acceleration down the electrodes. Ahhhhhh basking in the newfound knowledge:) i always wodered what the point of this was, now i know
this was one of the things i was reading
http://www.aa.washington.edu/AERP/ZaP/P ... humlak.pdf
Its a very low energy machine, the geometry is subtely different from a normal DPF, but the principles at work are the same. Also, theway they initiate a discharge is different, instead of using a straight pressure fill, they use a vacuum, then pulse a burst of gas into the area where they want the discharge to start, interesting........The only thing is that the gas pulse isnt short enough, and after the plasma is gone down the rails, there are still remenants of gas being shot into the same area and bieng pushed dwon the rails, so instead of having a clean sharp all at once discharge, down the rails into the pinch zone, it is more like an initial mega pulse and then just muck following it wasting energy.
3l
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Re: z-pinch instabilities

Post by 3l »

Yep that is the advantage to pulsing in a symetrical containment grid. You get the same effects as the
DPF but it is not asymetrical as in the usual Mather Type DPF. By being nice and round rather than a lozenge shape charge and current is evenly distributed, and does not have to rearrange due to induced currents, it hanges together longer and take less juice to move it together. That is why I like and pursue Dr Miley's work. The pulsed fusor alows high peak power and most importantly time for the grid to
radiate heat away so it doesn't melt. In Richard Hull's
pushing me into using a relaxtion mode of pulsed fusor operation I discovered you can puff a jet of deuterium gas into the center of the fusor just before the fusor is in an "on" cycle and do virtually the same as the folks in Washington State.

Fusion is fun!
Larry Leins
Fusion Tech
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