Why isn't parallel circular plate design used?

[2tankjones]

Why isn’t this plasma focus device used? – 2 parallel circular plates diverging in the middle. A power source is connected around the perimeter, outer edge, of one plate. The perimeter, outer edge, the other plate is connected to ground. Atoms are ionized as current starts to flow from one plate to the other (or ionized atoms could be injected between the two plates.) An external magnetic field or the “input angle” of the power leads can induce rotation of the ions about the center axis of the plates. (It would be interesting if the optimal rotation resembled the same logarithmic structure of spiral galaxies.) As the plasma spirals toward the center, plasma filaments start to form. As the ion/magnetic field approaches the center, the plates start to diverge extending the length of the plasma filaments. The filaments combine into a single filament then a plasmoid. (Like rubber bands, the more stretched and twisted they are, the more they bunch up when released.)

The spiraling helps to stabilize the plasma so that the filaments arrive at the center at the same time. The trick would be for the filaments to “collide” in a quick and efficient manner, (inverse of a pebble dropping into still water. )

Attachment shows a simple diagram

question along the same lines was posted, “Planar DPF – would it work?” 23 July 2012 04:59 PM

[Convergence]

Someone will correct me if I am wrong but that looks like half a hypocycloidal pinch device with a spiral. I have read the final NASA reports written by Dr. Lee. It formed two hot spots that were relatively long lived(that may not be a good thing). As I see it, it might be very hard to predict because you are combining the runup phase with the radial inward phase and that changes velocities, currents, forces, etc. In addition I don’t know that it will form the type of hot spot(collapsing plasmoid) that we all want. I think you are correct that filaments are essential for formation of a structure with the type of instabilities desired. It seems to me as complicated as the models are the only way to know is to build one and see. Anyone else?

[asymmetric_implosion]

It looks more like a Z-pinch than hypo-cycloidal pinch. You need three parallel plates for a hypo-cycloidal pinch so you can drive an axial implosion. You are driving a largely radial implosion like in a plasma focus but without the axial phase to stabilize the plasma flow.
Pure radial implosions have a large number of instabilities that you need to over come.

[Convergence]

The device looks like half a hypocycloidal device not the process. Maybe I am visualizing it incorrectly. Have people tried radial pinches and failed. It is hard to find out about the devices that didn’t work. It seems so much was attempted in the 60’s and 70’s and then the government just abandoned the thought process. A pitty if we have to relearn. The experienced individuals are aging and without programs a lot of that knowledge is in danger of not being passed on and being lost.

[asymmetric_implosion]

Z pinches are one of the most common implosion type radiation devices. The Z-machine at Sandia National lab is the largest such device in the world operating at nearly 26 MA with a rise time of less than 100 ns. A large PF device is 3 MA with a rise time time of up to 10 us. Z-pinches are largely used for nuclear weapons effects simulations and fundamentals studies of dense matter (stellar stuff) as they produce copious amounts of x-ray radiation. The preferred mode of operation is to use wires of high Z metals strung in two layered cylindrical arrays of many fine wires. A typical ring of wires can be more than 200 individual wires. Gas puff technology is viable for such devices and on occasion layered shells of gases are used as the radiating material. Published works suggest the Z-pinch devices are under performing compared to PF devices with a pure deuterium fill. A number of hypothesis exist as to the cause.

The plasma focus was an accidental discovery that happened to mimic the Z-pinch. The advantage of the PF is the less expensive pulse power system as it operates with a slower rise time thus less voltage to drive the plasma. The two primary stages of operation, the axial flow phase and the radial implosion phase, seem to produce a more stable pinch in a plasma focus. The Z-pinch is a pure radial implosion. The PF never took off for a few reasons: some political as the chief advocate for PF devices in the US had personal problems that made him appear unreliable, the PF devices tended to shatter insulators at increasing current which remains an issue in the classic PF design, and historically poor performance compared to Z-pinch devices.

The political issue was unfortunate but people are involved in science and some times our issues get into the work. The shattering insulators was a perception issue as much as a technical issue. No one in the Z-pinch world thinks twice about polishing key components and rebuilding switches are every shot. A drop in piece of ceramic doesn’t seem so bad by comparison. There are also effective alternatives to a solid, plasma facing insulator. More needs to be done but the initial results done in the 1990s were promising. The historically poor performance was a result of poor understanding of the PF process. Most people looked for thermal fusion which the PF does not do well. The non-thermal fusion, fusion driven by fast ions generated in the pinch, was frequently put down by those in the fusion community as unreliable and unpredictable. I think recent work has caught the attention of more open minded folks and showed them that reproducible and predictable are at hand. There is also a bit of a sense of that fusion must be hard. If our best minds have not cracked it yet, it must be very hard. I don’t know that I agree but I think there are options of fusion that are yet to be explored using the best knowledge of modern plasma physics. Is there an approach that is vastly to superior to all other approaches? I don’t know but it seems less and less likely that NIF or ITER are going to reach the goal of fusion energy and be economically viable in the current financial climate.

[Convergence]

If no one ever tells you, I will, you sharing your insights, knowledge, and perspectives are greatly appreciated. I have been closely following these sights since I think about 2007 and spent many enjoyable hours reviewing different posts and papers(when they aren’t behing paywalls). I am of the opinion that Eric Lerner is truely a visionary and his work is keystone that leads to many possiblilities. It is not the device but the plasma structure and process that is important. The inward decaying plasmoid is the key. We don’t have gravity to work with so EM forces are the most logical substitute. I have run accross a couple of papers describing mathmatic models of the process of the inward decay of a plasmoid and how the filaments and there coalescence are important(sometimes I can only comprehend the abstract). The models may or may not be accurate but it seems to make sense from a conceptual point of view. The struggle with filament formation is one of the many reasons that I think this research is likely to lead to useful breakthroughs. I agree with you about the tokamak and the ITER. I can’t imagine how those programs ever get to a viable process. A keystone can unlock a multitude of potentials.

[2tankjones]

I read the article by Dr. Lee from NASA. Good work. General principle of cycloidal plasma collapsing into a toroidal pinch was confirmed. I don’t think the configuration was the best. I guess the quickest and easiest way to find out would be to build several different configurations, test, and follow the data. Hmm.

[2tankjones]

Both coaxial and planar cycloidal configurations create long plasma filaments that are structured in a way that the middle of the plasma filamensts merge together and spin much faster than the ends of the plasma filaments. In my minds eye (and playing with a rubber gum eraser) The difference in rotation causes the fillaments to entwine around each other causing the characteristic loops to form that when combined make up the plasmoid. I am guessing conservation of angular momentum and conversion of magnetic field energy defines the structure of the resulting plasmoid. The gum eraser always buckled and formed that characteristic plasmoid donut loop at the point where the diameter was smallest. The ends of the filament were moved inward and twisted at a specific rate that corresponded to the loops diameter. (One full twist of the “filament” created one full loop making up the plasmoid with the filaments ends coming closer by the distance of the perimeter of the loop. approximately.) Coaxial DPF does a nice job of spooling a plasma filament into a toroidal shape. I am guessing but not sure that the planar cycloidal DPF would do so as well but be able to do it over a longer time span with a lower peak current and more efficiently getting energy into the plasmoid.

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