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Lerner wrote: Question to assymetric implosion: Did you ever calculate the stresses and impulses invovled with your insulator? We are running at 1 MA and intending to go above 2 MA, so we need to know in advance what tolerance we need to achieve.

Simple calculations were done but I wasn’t the one that did them. Our cathode (anode pointing skyward in our case) does not move the hardware at 0.25 MA in an appreciable way as determined by experimental testing. The calculations supported this conclusion.

I would point out that imperfections in the alumina can cause problems. I’ve encountered “bad” alumina that has voids or smaller scale imperfections in the past. I would like a second opinion from one more knowledgeable but I speculate that local defects increase local stress making it easier to break. Once a fracture starts the insulator is broken in a shot or so. This was my hypothesis with quartz. I could fire 1 or 2 shots before it breaks. My best suggestion is to increase the alumina thickness and buy the highest grade alumina which should have minimum defects. I use 1/4 inch alumina without any problems at 0.25 MA. My guess is other 1-2 MA machines use much thicker insulators to avoid the shock problem.

I mention three other options but all have problems and cost money. The first is to tie the anode and cathode together mechanically using nylon or some other insulating ties to limit the motion. The problem is how to tie the two together without flashing over. The second is to make the plasma focus a tri-plate instead of a bi-plate. If you carry the cathode current in two plates that surround the anode (cathode-anode cathode sandwich) you should be able to balance the force on both sides of the anode and it should reduce the impulse. The same problem as the first; how do you get the current to flow through the anode without a short. Techniques like these are used on >2MA Z-pinches which have large impulses. Tri-plates are the norm for large machines to reduce the impulse of the current pulse and reduce inductance. The problem with tri-plates is they tend to flash on large voltage spikes (like the pinch) splitting your current. The third possibility is to change the insulator design from a hat or reduce the radius of disk. I found that reducing the disk radius improved insulator survivability during assembly. I typically make the disk diameter just 10-30% larger than the outer diameter of the cylinder of a hat insulator. It is just enough space to put a thin o-ring in place on both the anode and cathode side to maintain the vacuum seal. I wish I could say more but I am straying into proprietary design information.

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I thought it was pretty fair. Fusion has been “our future” for over 50 years and it hasn’t delivered. That doesn’t mean it won’t someday. There are certainly political issues around ITER and NIF. One would expect that given the scale of the projects. My opinion is ITER has more political problems than NIF because of the number of countries involved. Scientists certainly participate in it (more by force than by choice in most cases), but the few fusion guys I know well are serious scientists that recognize the massive technical challenges before them. They are have no intent on wasting money or misleading anyone. They want to figure out if their solution works or not. My opinion is that ITER will not be built to full scale if at all while NIF enjoys funding for years to come.

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Sorry to hear the insulator went. I guess it will be 4-8 wks before more data is taken while the insulator is made unless you have a better supplier than I do. I use the hat insulator design as well.

Only one material that I know of has better properties for a plasma focus insulator than alumina and it is far from cheap; diamond. Many other materials have been tried but each has a problem. If you are looking for a cheap solution that works OK, I suggest alumina silicate. I’ve use it in my PF as a cheap alternative to alumina when I’m trying something new. Alumina silicate is easy to machine but it is not as mechanically robust as alumina. You need to be careful about weight distribution on the disk part of the hat. I’ve broken more insulators installing them than by running the machine when using alumina silicate. Other materials that might be useful are zirconia but last I checked no one could make it in the shape you need. Diamond has the same problem. I know people love glass and quartz as an insulator but I’ve never had a good experience with either. Quartz needs to be heat treated properly and no one has gotten it right for me. Glass works OK but more fragile and more expensive than alumina silicate. I can suggest a vendor but again, some change to the cathode might be required because glass cannot be made with a tight corner at the disk-cylinder interface and be strong.

My best suggestion is thicken the alumina wall where it is breaking. I know it’s a pain for the pulse power design but it does help. I’ve run a single alumina insulator at 0.25 MA for over 25,000 shots from ~5000 shots by increasing the wall thickness by 20% in the vertical section of the hat. If you are breaking on the flat disk section, you have a tolerance problem or a weight distribution problem. Both are a pain to resolve. To my knowledge very few machines above 0.5 MA have an insulator lifetime of more than 1000 shots. Nasty plasma environment coupled with shocks is not a recipe for a long insulator lifetime. High grade alumina (>99.6%) might have some benefits as well given that it is closer to sapphire, but I use >93% with great success.

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TheMagicalBadger wrote: Just a quick thing regarding definition of education levels, from a global perspective:

Good point. I guess the next logical step would be to list the math background (calculus, algebra, differential equations) and the physics area (optics, electromagnetism, plasma physics) at each topic section to warn the reader about the topics discussed. My problem with this approach is saying optics does not necessary suggest the level. More to think about…

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annodomini2: A good suggestion, thanks. I don’t know of the math resources are available on line in a nice form. Wikipedia and other such resources seem to be written for people “in the know” with a memory problem. I will put some thought into how to incorporate the math and physics and not overwhelm the reader. I might assign each section level of math and physics background. My concern is the math used even in simple models tends to rely on college level math usually taken by physical science majors. I can speak only from my college experience in engineering but we took a minimum of 5 semesters of calculus and related topics. Most took at least one or two more courses. That is a heavy burden for the curious reader that wants to learn a bit more.

Patientman: Wow. I knew this would take some time and effort, but now that you laid it out it appears pretty big. My thought was to address a few high impact areas initially. The web site idea seems to be a better choice right now as the script is in development. I prefer a written medium because the reader can re-read the section to better understand the details. As I mentioned above, I think I would assign a rank or a grade to each section to give the reader a heads up before they start a section. My thought was to start the following:

-high school education with little physics-> relate ideas in terms of everyday life as much as possible. Skip the math and talk about concepts and ideas.
-high school education with high school math and physics -> show a few basic equations with algebra
-college (undergrad) general education -> up the math and physics a bit that would be expected of a college educated person.
-college (undergrad) physical sciences -> Break out the equations and discuss details that would bore or confuse the levels below.

I don’t have any intention of going beyond this for one main reason; beyond the undergrad level researchers really need to read the literature after formal training. This level of discussion and debate takes place at several meetings each year that are later distilled into papers, books and other academic mediums. If one has this level of interest, time to subscribe to journals and go to the meetings.

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TheMagicalBadger: Thanks for the suggestions. I like the structure you suggested so the reader can stop at a comfortable level. My plan was to keep the math and physics to high school level whenever possible, but I think these concepts need some math to support them. My thought was to start with pulse power because it is reasonably similar across all plasma focus devices. The basic components are the same in most plasma focus devices so it would be a firm footing for everyone to start from and hopefully agree on. Inside the vacuum chamber is when I expect the disagreements to begin. Many theories exist on what happens inside and most of them remain valid because of a lack of experimental data to confirm or to refute. I hope to present a few different options so the reader can see the differences and decide about which seems the most plausible.

I’ve started jotting down some notes and ideas about the presentation but a simple cohesive message is going to take a bit of time. I also expect others will have revisions, suggestions and most definitely editing before it becomes a useful tool.

Lerner: I would be interested to see an explanation of nuclear physics and quantum mechanics for people with little background. It is a big undertaking. I wish you the best of luck.

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Lerner wrote: I think this is great. I really don’t see your beef, zapkitty.
What is the form you see this educational material being put into, AI? A webpage, pamphlet or what? I know it is ambitous, but lots of folk say we need more videos these days.

I don’t know yet. I was thinking about starting with something text based so editing would be easy. Once the text was satisfactory, we could go with a video to speak to people easily.

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Jamesr, thanks for the info. I’ll add it my list. I was going to get a bit more technical and talk about things like capacitor lifetime, the design considerations, switch limitations, role of inductance, etc. Too much, too little, too confusing? I would appreciate direction input as much as technical input.

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zapkitty wrote:

What is pulse power?

I’m rather afraid that, [em]despite the best of intentions[/em], that it may wind up being an excuse by vested interests to add an unneeded $5,000,000 talking point to any discussion of FF funding and applications.

And I ask again: if what FF has built up is working now why insist on talking up the 5 mil solution?

The “best intention” was to educate folks on the boards about the plasma focus. My plan was present the state of the art in each technology so people could understand how the technology works and not express my personal opinion on the next step. I welcome input from others as they might know things I don’t.

Again, I answer that it was a suggestion for moving forward. FoFu-1 is working but the point was to help others understand it. Some posts leave me feeling that some folks don’t understand the technology behind the PF and want to know more. My intention was to help.

My question to you, what is my vested interest? Do you know? My guess is you do not. I offer you this; I don’t care if conventional pulse power, the LTD or some other pulse power scheme is used on the next generation of FoFu. It was a suggestion that might overcome some of the technical challenges that I know are dogging FoFu-1. I am familiar with the problems as I have faced them in my devices. My vested interest is saving others the growing pains that I suffered in my experiments. Beyond that, people can use the information as they see fit.

I don’t work for the oligarch or the man or some other nefarious entity. I work for a small business very similar to LPP with a different goal for the plasma focus. I’m no more the “bad guy” than anyone at LPP.

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An experiment that might interest you and clear up some of this discussion. In 2007 a paper was published from Sandia used deuterium fuel gas in the Z-machine. The fuel gas was stored at the cathode potential (-4 MV, much closer to the peak in D-D fusion cross section than 100 keV.). This is common practice in Z-pinch machines. No increase in radiation yield is observed as your hypothesis suggests. Similar experiments are conducted on plasma focus devices without any significant increase in radiation yield. You can argue that the pinch devices are fast pulse machines and the fusor is a DC device, but the time to bring the fuel gas to the local potential is a fraction of a nanosecond while the pulse duration is >100 ns.

I wish you luck in your experiment but based upon the existing data you will not see an increase in fusion yield over storing the fuel at anode potential or some other potential.

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I’m a bit confused by the video and it seems like you are glossing over a few important points in the physics. You mention alpha particles being created in the fusor; are you using D-T fuel or a p-11B fuel? D-D fuel cannot produce 4He in a low pressure environment due to momentum conservations considerations. If you are referring to D-T or p-11B, why does the alpha particle only have 100 keV? Shouldn’t any particles created in the fusion event have their fraction of the change in binding energy (14.1 MeV in D-T) plus the potential difference of 100 keV. In that case, the 100 keV seems pretty small compared to the fusion yield. Could you clarify please?

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I was referring to the next step. Lerner stated that $30-50M would be required for the next step. My comments are directed at that statement. You can build an LTD DPF for $6M at the 1 MA level for the same pulse power and it’s highly reliable compared to the existing pulse power firing thousands of shots per day. The reports indicated that problems with the switches have caused a substantial delay. Why reinvent the wheel? The price of the LTD drops if you reduce the repetition rate from 1 Hz to say 1 shot per minute which might be enough for the next step. At 1 shot per minute you can use conventional pulse power as well but given the problems encountered thus far, why not buy a product that is engineered and tested vs. building your own? Both systems are capable of the same current, inductance and rise time (key factors for a plasma focus). If the custom pulse power can be built for less, that would be great but the problems to date suggest less expensive components were used and they paid the price for a long time patching the cheap components together and making them work. It’s always a compromise in research to purchase the proper quality of components because labor typically costs far more than materials in the end. Time wasted patching lower grade components tends to be far more expensive than buying the right part in the first place. I believe the saying is penny wise, pound foolish. Each group has to decide on a strategy that works for them but I think most companies find that buying something that works “out of the box” is worth the cost in labor. Universities rely on cheap grad student labor so they can get by using cheap components because the labor is inexpensive.

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Why stop at a billion? What distribution are you assuming to calculate your 1 in 14,000 chance of having 5 shots in a row that are within 3%? I think you will find that literature suggests a non-normal (non-Gaussian) distribution of radiation yield from a plasma focus. My concern is you don’t know the distribution of your radiation yield yet so claiming that 5 shots is statistically significant seems premature. In my way of thinking (engineer not physicist), each time you fire a shot you are sample the machine’s inherent distribution at a fixed set of conditions. You need to sample the distribution many times before you have confidence in it.

I’m not trying to say that the result is not exciting, but it is not unique. I appreciate that the typical standard deviation in most PF devices is ~ 50% (my PF is 46-53% depending on conditions) and you have demonstrated far better than most, but not all. Ahmed et al (doi:10.1088/0741-3335/48/6/003) showed 5% a few years ago in 10 shots using alpha particle pre-ionization. I believe your combination of the cathode near insulator and initial magnetic field are the reason for this. It is something that many others have not adopted yet.

I also appreciate the problems you’ve had with the pulse power but a reliable 1 MA drive that is demonstrated to operate at 1 Hz all day long at 100 kV costs about $5M. The electrodes and other components can’t cost more than $1M. Look up the linear transformer driver papers by Sandia National Lab. The LTD has rise times up to 800 ns. It seems that would go a long way to solving your pulse power problems in the next few years. Just my opinion but $6M seems better than $30M. Best of luck in the upcoming campaigns. I look forward to a paper on the statistical significance of the data later this year.

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Wow, great result on the high energy x-rays. I agree that quality is important but quantity is a big deal as well. The result of 5 shots of repeatability was nice but it’s a far cry from what I would call statistically significant. A hundred or thousand shots would be far better. I know this requires a great deal of engineering on the pulse power and other components but that is the long term goal right; operating at ~10 Hz all the time. It sounds like the physics is being sorted out nicely so when is the engineering of the pulse power going to begin?

One questions: where are the x-rays coming from? Are they generated in the pinch itself via brems or are they coming from the anode brems? I thought LPP had a diagnostic for hard x-ray imaging develop by Dr. Murali. I’d love to see the pics if they exist. I find the HXR images more telling than visible images.

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The plasma focus can and has been reproduced many times. The problem is the LPP has a patent or two on the technology. The patent owners have the rights to the technology so even if it is easy to reproduce no one else can do it and make money or produce products such as reactors. You can hate the patent system but it is the law. The patent owners would surely fight hard to protect this breakthrough for the duration of the patent. These is also the issue of others patent on parts of the technology. Several groups own patents on different aspects of the plasma focus. They worked hard on their pieces and will want some of the pie when the time comes.

When fission was first commercialized the strategy was that electricity would be so cheap they would give it away. That ideal was never realized. FoFu is likely to have the same fate. The technology will be locked down by patents and sold to the highest bidder. If one group or company buys up all the relevant patents and people the energy future is owned by that group.

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