[Francisl]

Henning wrote: That article requires a login, but it’s also available at the following location, which doesn’t need a login:
http://rsi.aip.org/resource/1/rsinak/v82/i10/p103506_s1?bypassSSO=1

Or direct download of PDF:
http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=RSINAK000082000010103506000001&idtype=cvips&doi=10.1063/1.3648117&prog=normal&bypassSSO=1

I was able to use my library card to access the science database on EBSCO through our Minnesota public libraries. There is a listing of 522 articles just on dense plasma focus. I’ve just started to browse these articles.
What information would be most useful to research now?

[Francisl]

Warwick wrote:

How do you validate the simulation?

It’s nice to know that we’re working on simulating plasmas better, but how can you validate that the simulation was programmed correctly? As a software developer myself, I know that every piece of code has at least a few bugs. Is there some kind of well known test-case to compare against?

The code for the next iteration will be open source so there will be some scope for interested people to try and spot mistakes for themselves.

There is some data already for example: Dynamics of the structure of the plasma current sheath in a plasma focus discharge.
I’m guessing that researchers will be eager to test comprehensive codes on their machines.

[Francisl]

asymmetric_implosion wrote: The quick and dirty of it… Neutron yield (Y) in a pinch device increases with the peak current (I) by a power law with a form Y=a*I^d where d is between 3 and 5. The coefficient a is not a constant (observed from experimental data). So, what parameters affect a? The answer is that the ratio of the pinch voltage to the charge voltage or more commonly measured the ratio of the minimum in the time derivative of the current to the maximum of the time derivative of the current (See graphic labeled Fig 5 for locations of these points). As the dI/dt ratio grows, Y divided by I^d grows leading to more favorable fusion yield (See graphic labeled Fig 7). The larger Z-pinch devices like Z and S-300 don’t fair well by this model while plasma focus devices generally do OK. FoFu-1 and AASC PF-2 do very well. The value of d from general least squares fitting using the 8 machines is 3.79. Want a better fusion source, maximize the ratio of pinch voltage to the charge voltage…well for D-D reaction anyway. D-T might have a maximum due to the low peak in the cross section at 100 keV.

That is some impressive work. I hope it gets published.
Can you use this model to predict the limits of your sampled machines?

[Francisl]

asymmetric_implosion wrote:

This part is new and something I’m working on with a hope of publishing later this year if the reviewer and I can agree. Plasma focus devices seem to perform well when the voltage generated by the pinch is large compared to the voltage used to charge the bank. When the ratio of these terms is large, the fusion yield is large. When the ratio is small, the fusion yield is small. The higher ratio implies that the mean ion energy that drives the fusion is higher, which is a good thing. Fusion cross sections grow quickly with ion energy.

FoFu-1 does well because it is able to produce a large voltage at pinch time. The small electrodes are an important part of the equation. It also seems that LPP is able to compress their pinch more tightly than most machines.

Please let us know when your paper is available for viewing. I’m already thinking of questions.

[Francisl]

Lerner wrote: Just to clarify–we don’t think we have tested the new tungsten “teeth” and our published results pre-date using them. We do think our results are due to the small size of the electrodes and the axial field coil we are using. I agree that neutralization of the current is a potential problem but how much of one it is needs to be determined experimentally.

asymmetric_implosion’s link led me to this paper by S Lee and S H Saw: Nuclear Fusion Energy- The Dawning of the Fusion Age
Section 5.5 “Operating the Plasma Focus Beyond Neutron Saturation- Ultra High Voltage and Current-steps” talks about the next generation of plasma focus devices using higher voltages for greater success.
I’m really just speculating here but I think that in effect the LPP device is benefiting from higher voltages. By carefully reducing power losses and using smaller electrodes I’m guessing that a smaller percentage of the capacitor charge is used in the axial phase and this leaves more charge and consequently more voltage for the radial and pinch phases. If a higher voltage translates to higher temperatures and if this is combined with the axial magnetic field, then a more efficient fusion process could be occurring. This could explain their progress and point a way to future experiments.
Does my reasoning make sense or is it bogus?

[Francisl]

asymmetric_implosion,
Please suggest some good websites we can use for information. It has been my experience that a lot of interesting articles are behind paywalls. Satisfying our curiosity can be expensive.

[Francisl]

I went to the https://focusfusion.org homepage and use the search term “ion beam”. A number of articles were listed, such as: LPP Team Starts Looking at Ion-Beam Energy Extraction and New record beams bode well for applications.
I think I read an article a couple of years ago that LPP demonstrated to an investor that the beams had reasonable directionality. I hope there will be a good way to extract the energy.

[Francisl]

Process Of Bonding Copper And Tungsten
This is not easy but may be a permanent solution.

[Francisl]

Could this high temperature plasma be used to operate a MHD generator?

[Francisl]

Can you post pictures?

[Francisl]

Here is a list of particle accelerators. Some of them would be capable of performing those tests. The problem is finding the funding to conduct the tests.

[Francisl]

Here is some related research. I don’t see any reference to hard data but maybe they could be convinced to collect some.

[Francisl]

On a related topic, since tungsten electrodes will be used, can the tungsten ions be used to measure the energy levels in the different parts of the plasma wave and pinch as suggested by this article?
http://www.sciencedaily.com/releases/2009/09/090909111623.htm

[Francisl]

asymmetric_implosion wrote: People have tried two PF’s facing each other on and off since the 1970’s. The tale is one of woe. It led to the design of the hypocycloidal pinch. Rather than two concentric cylinders, the hypocycloidal pinch uses three ring electrodes. The rings are stacked in a cathode-anode-cathode configuration. A plasma is generated by flashing an insulator, like a PF, at the larger diameter. The plasma runs toward the center like a Z-pinch but it turns the corner at the of the rings and implodes. The pinch lifetime was observed to last for 10-100X longer than any pinch device at similar densities (~1E19 /cc). As a general rule, a pinch can hang together longer if the density is lower. A single NASA tech report was written and the idea was abandoned. I don’t know why. I would post the report but it is huge. I’ve wanted to test this idea in more detail as the beam damage and x-ray deposition should be significantly reduced due to geometry. The key problem that I observe is the energy stored in the pulse power is much larger than a PF so the energy released per shot must be larger.

I think I found two of the articles that you are referring to: INVESTIGATION OF HIGH ENERGY RADIATION FROM A PLASMA FOCUS FINAL CONTRACTOR REPORT NASA Grant and DENSE PLASMA FOCUS PRODUCTION IN A HYPOCYCLOJDAL PINCH.

This led to an article about using the hypocycloidal pinch as a high power trigger switch: Studies of the Plasma Puff Triggering Mechanism of Inverse Pinch Switch. Would this be practical now which is nineteen years later?

[Francisl]

I agree that the current designs should continue. If electrode failure becomes a problem then other designs can be considered. I was trying to spark a conversation about other possibilities that may be improvements. A few months ago someone brought up the idea of two dpf units facing each other. That idea didn’t go anywhere. Essentially, that is what I was trying to depict with the pinch occurring in the space between the two dpf units.

An alternative is to use a single dpf with the electrodes designed to maintain the pinch outside of the central electrode.

[Author]

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