Where's the beef?

Discuss how polywell fusion works; share theoretical questions and answers.

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Tom Ligon
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Post by Tom Ligon »

My comments on WB2:

I was not especially impressed with the diagnostics we had available for WB2. The budget was so lean when that thing was built, that was not even a PMT, it was a lead-sulfide photoresistor purchased surplus for a few dollars, and calibrated against various roughly-known ambient light sources, including daylight.

Before I came on board, the data acquisition inputs were unfiltered, which means the signals were all recorded with a grossly invalid Nyquist criterion. They are bands of fuzz with some underlying shifts. They also blew about one data acquisition card a week due to having no protection on the inputs. I fixed both problems before running a single test.

I know they did some Langmuir probe tests, but with a single-tip probe. I have no idea how to get valid data out of a single-tip probe in a magnetic field, and don't trust any of it.

The power supply was a wimp, a little 1 kV Glassman that put out something like an amp or less. In the bright discharges, it usually went into current limit mode and pulled down to a few hundred volts.

The bright discharges, in my opinion, were an undesirable state, and I think Dr. Bussard concluded the same thing after more experience with the big ones. They did show something useful: they were bright only inside the magrid, with faint wisps showing at the corners. You could SEE the trapping was occurring, the question is if the machine ever achieved a proper wiffleball. From the shape of the bright area, it may have.

The machine was hopeless for fusion, but in the last week of its life we hooked it up to the supply built for PXL-1 (10 kV 1A, unregulated) and destroyed it at 4.5 kV.

WB2 should be regarded as a really rough first crack at building a proper magrid machine.

Tom Ligon
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Post by Tom Ligon »

My comments on PXL-1:

On the day of my interview, PXL-1 arrived from the welder, and I helped move it in. It mystified me from the start. I had no clear idea how Dr. Bussard intended to get it to work. The Hirsch-Farnsworth made sense in an instant ... I had thought of trying something like it myself back in college, but my health physics professors said nothing like that would ever work, so I failed to dig deeper and find out it had already been invented and worked better than any other fusion experiment at the time.

I even made some sense of WB2, although I just had to take Dr. Bussard's word for it that the power balance could really work out. Polywells really do take some head-scratching. For simple machines they really do some complex stuff, and I was not going to get it in one 2-hour interview.

PXL-1, especially as he had me configure it initially, made no sense at all to me. In fact, that initial configuration was flat wrong, and I actually caught Dr. Bussard in a conceptual error on it. The first configuration had a grounded cathode with a positive accelerator grid, with a strong permanant magnet in it to partly magnetically insulate it. The walls are grounded, and the magnets are outside. In this configuration, the accelerator grid would be the only loss path for the electrons.

The flaw was, the main body of the thing would never have hot electrons. As soon as they passed the grid they would slow down. We put three single-tip unbiased Langmuir probes in it (i.e. just voltage measurement probes), and I measured a negative potential well of a few tens of volts. Dr. Bussard was sure I'd screwed up the polarity, because he thought the voltage should be positive. Here, my instincts trumped his math, because every electron I ever met was of the negative persuasion, and an abundance of them would just naturally be negative. The probes were not measuring kinetic energy, but potential. Thus, when Dr. Nebel says to remember, in these electrodynamic machines, that electrons have mass and momentum, I smile. That's why there was a negative, if shallow, potential well in a machine with no applied negative voltage, and it made absolute sense to me that it would be that way. They were happily, if a bit lazily, rebounding across a magnetically insulated drift region, and were coverging in the center.

Once he finished slapping himself over that error, we reconfigured to the hot cathode configuration I mentioned earlier, and the machine started to do amazing things I still don't fully understand.

PXL-1 had much better diagonostics, including an RGA, and a proper photomultiplier tube (end-type, magnetically shielded, and mounted on a long tube to minimize errors due to the magnets), looking thru a tight H-beta interference filter. I believe that was also about the time we bought a spectrometer set up for the blue end of visible light, with the hope of catching some Doppler broadening.

Running PXL-1, I became convinced the bright discharges were useful mostly for cleaning the walls, and the interesting science came before, especially just before, they lit off. The most interesting phenomenon I described elsewhere: modes in which the cathode and return current suddenly dropped. These seemed to be preceeded by a distinct difference in cathode and return current, and the final test in the series resulted in a major release of energy only possible if the thing had been acting as a 3D electron storage ring. I have no doubt it was an extremely effective high-energy electron storage device, and I still wish I knew if it was a full wiffleball or some other effect responsible.

I also saw it converge ions visibly at the center on several occasions, when it was nice and dark and had a deep potential well, as much as about 7 kV. The effect was faint, but I think there are a few photos and a video tape that just show it.

Problems with dispenser cathode poisoning led us to try simple tungsten filaments in PXL-1. They worked, but did not emit as much current, and the light output interfered with the photometry.

We first tried microwave ionization on PXL-1, by putting a common microwave oven magnetron on one CF plate, the antenna sticking into a machined-out conical cavity. The particular tube fortunately could be mounted vacuum-tight to the plate. This thing worked like a champ, lighting up the 875 gauss topology in the machine beautifully (that being the field for ECR at 2.45 GHz). If nothing else, you could see the field shape clearly. The bright glow mode blasted this etherial structure away, so I could not use it to demonstrate push-back of the field. The extra ions tended to encourage the bright discharge, and I think all of my deepest wells may have been achieved without microwaves.

I did some work with more sophisticated Langmuir probes on PXL-1, including double-tipped, and attempts at sweeping the differential and measuring the S-curve. My results never looked much like the textbook. The probe that seemed to work best had a fixed differential set by batteries, floated at the local potential of some thousands of volts, and the current measurement was transmitted by fiber optic cable. This presumably gave a reasonable density measurement. We also tried it on WB-3.

PXL-1 was flawed, but interesting enough that Dr. Bussard tried fixing the flaws with WB-5, which he finally decided was a red herring that tragically delayed his trying WB-6. I still consider it the most interesting machine I worked on.
Last edited by Tom Ligon on Sat Jul 12, 2008 3:01 am, edited 3 times in total.

Tom Ligon
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Post by Tom Ligon »

WB-3:

WB-3 was scaled up in each dimension by 2x from WB-2. It still had square cross section coils that touched, so it had the bad loss paths including funny cusps.

It had the full diagnostics package from PXL-1, including microwave injection to boost ionization. It was equipped to inject deuterium.

We did conclude the 2.45 GHz microwaves were too low for the magnets, as the 875 G topology was too deep in the machine. We needed ECR at more like 2 kG. We bought an expensive tunable TWT system, but never tried it on WB-3.

By the time WB3 was in operation, I was totally convinced the bright discharges were to be avoided. The power supplies available, including the big switchers we installed in San Diego, could not drive it to a deep well once the bright discharge lit off. My attempts were to run successively higher test voltages, attempting to "clean up" the machine and avoid the release of gas the RGA told me was triggering the bright discharges (this was mostly hydrogen, and it would swamp out the deuterium). What I was seeing was the effects of electron hitting the funny cusps and coil corners at high energy. I was able to push it to around 7 kV of drive voltage, but never to fusion conditions. Had we built it in the shape of WB6, I think we would have been able to drive it to fusion conditions, and furthermore I think we could have held quasi-steady state for many seconds. I belive I did achieve deep wells on that machine for periods of 15-30 seconds.

Magnet heating was a killer, since it took hours to cool off after a long run, and I rarely got more than four shots a day.

The disappointment for me was that WB-3 never exhibited the sudden drops in current seen in PXL-1. I was seeking that condition. It sounds to me as if WB-6 may have been doing it, as I gather it drew hugh current initially, settled to a more modest level (if 14A is modest) and made fusion at that point, then fired off into Paschen discharge and drew down the capacitor supply. We suspected it needed a larger supply, but it also clearly needed the better shape.

WB3 did add a video overlay system, in which the computer data could be placed on one side of a videotape image.
Last edited by Tom Ligon on Sat Jul 12, 2008 3:09 am, edited 1 time in total.

Roger
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Re: What will it take?

Post by Roger »

pstudier wrote: going from $2M to $200M seems quite a jump. $20M would be justified if the published results gave
A 160cm WB-8 would be doable for 20 million, no ?

And lets say WB-8 cranks balls, we just proved scaling. We'll still need to build

A dodec. Maybe 30cm.

Build a carburetor, LN2 cooled for 10 minute runs. PB-11 too.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

charliem
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Post by charliem »

Tom Ligon wrote:WB-3 was scaled up ... I was able to push it to around 7 kV of drive voltage, but never to fusion conditions. Had we built it in the shape of WB6, ... I think we could have held quasi-steady state for many seconds.
Redoing WB-3 in the shape of WB-6 should be cheap enough. Do you think it could be interesting?

I'm thinking mainly on obtaining/confirming data about much longer time scales without spending too much.

Art Carlson
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Post by Art Carlson »

Betruger wrote:
seedload wrote:If there is no beef, kill yourself a cow! Sounds like there are some freshly ground burgers in the freezer and hopefully a big picnic planned for the end of the summer.
Someone invite A.Carlson :)
Count me in. I only asked the question because I'm always hungry. Actually finding and killing a cow may not be as simple as some of us would like to think. Just ask a physcist how to milk a cow. "First, let's assume that the cow is a sphere with 1 m radius, and that the milk is evenly distributed, ...."

Art Carlson
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Post by Art Carlson »

rnebel wrote:Wiffleball data:

When I first got on board with EMC2 I looked through the files for data from the WB-2 and the WB-3. I found some data sheets, but they weren't very helpful. From discussions I had with Dr. Bussard, I believe that the way he surmised the existence of the wiffleball was to look at the total light output with a PMT. What was observed was that the light intensity peaked as the magnetic field decayed. The interpretation was that when Beta=1 was achieved (by lowering the field) the plasma leaked out through the cusps so the light intensity dropped. Tom Ligon might want to comment on this since I suspect he was involved with the data.
Do we at EMC2 believe this is reliable? No. My understanding is that you can see the same kind of behavior in helicon sources which are nowhere near Beta=1. Am I concerned about this? No. You'll just have to stay tuned.
This sounds like confirmation of my impression - from Rick Nebel, who has at least 1000 times more information than I - that the data on and understanding of polywell operation, published or not, is very thin. The comments by Tom Ligon are not so direct, more a technical narrative, but seem to show a similar picture.
Now if some of you think that the potential payoff compared to the cost is large enough to justify spending a few million dollars, a couple years doing experiments, or countless hours hanging around this forum, then I can understand that. I only ask you to remember that the experimental as well as the theoretical basis of the concept is extremely speculative.

Art Carlson
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Post by Art Carlson »

Tom Ligon wrote:I know they did some Langmuir probe tests, but with a single-tip probe. I have no idea how to get valid data out of a single-tip probe in a magnetic field, and don't trust any of it.
Tell me about it. I spent a good chunk of my career trying to figure out how Langmuir probes work in a magnetic field. I completely sympathize if you choose a different density diagnostic. (Just don't try to fly blind.) After a great deal of effort, my conclusions were (1) that nobody really understands them, and (2) that they give roughly accurate results anyway. The frustration with this experience was one of the factors that led me to leave plasma physics.

tonybarry
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Post by tonybarry »

Hello Art,
Speculative? Yes.

Can it be tested to see if it can work for less than 1e9 US dollars? Definitely.

Worthwhile? That's a personal decision, but I think so.

I am not a physicist, (I work in medical research) so I have some experience of promising ideas that don't pan out (and some that do).

By the way, Art, I have really appreciated your input to the forum. Thank you for putting in the time and effort.

Regards,
Tony Barry

drmike
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Post by drmike »

Thanks Tom! Makes me feel like I can actually do something useful in my basement....

Helius
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We need to think "expected value"

Post by Helius »

Art Carlson wrote:...Now if some of you think that the potential payoff compared to the cost is large enough to justify spending a few million dollars, a couple years doing experiments, or countless hours hanging around this forum, then I can understand that.
I read your comment to mean that despite the slight and negative spin, you also see the expected value of this research as extremely high.
...I only ask you to remember that the experimental as well as the theoretical basis of the concept is extremely speculative.
... And a few million dollars and a couple of years will remedy that...

Art Carlson
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Re: We need to think "expected value"

Post by Art Carlson »

Helius wrote:
Art Carlson wrote:...Now if some of you think that the potential payoff compared to the cost is large enough to justify spending a few million dollars, a couple years doing experiments, or countless hours hanging around this forum, then I can understand that.
I read your comment to mean that despite the slight and negative spin, you also see the expected value of this research as extremely high.
understand != agree
I think the expectation value (in the mathematical sense) is low. Of course, a cheap means to produce fusion power would be an unimaginable boon, but you have to multiply that by a very small probability of success. The up side by itself is not enough to justify spending the millions. Think of Pascal' Wager.
Looking at it another way, given that there is not enough money to pursue every suggestion, where should the available money best be spent?
  • Looking at the polywell, I would rather spend it on theory and simulation than experiment. (The chance of guessing the right configuration without a theoretical understanding is close to zero. If you can show theoretically it can't work, you've saved a bunch of money, but if one experiment doesn't work, it can kill the program, even if another configuration would have worked.)
  • Looking at (alternate concept) fusion, I would rather spend it on FRCs.
  • Looking at energy, I would rather spend it on solar thermal in the desert and hot dry rock geothermal.
On the other hand, non-mainstream fusion research has always been partially justified by training new fusion researchers and understanding more about basic plasma physics. From this point of view, it is hard for the polywell program to be a complete waste of money.

Aero
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Post by Aero »

Do you think then that the Naval personnel responsible for managing and securing funds for this project are overlooking the need for a detailed physical understanding of the process and funding the experiments for whatever reason? I doubt it. I do think that perhaps Dr. Bussard's past career and status did influence some of the early awards. How could it not, the man was widely recognized as a pillar in the field. But I could not guess to what degree it influenced and I suspect that it no longer does.
I think that we now have a real physics research program and if the peer review results in further funding, I expect it will be a well balanced effort focused appropriately on both theory and experimentation.
Aero

rnebel
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Post by rnebel »

A few comments:

When we came into this project we took the attitude that we didn’t believe anything that was in the data. There are a number of reasons for that. First of all, we were tasked to find out if the WB-6 data was real so we had to be skeptical. Secondly, Dr. Bussard had had a lot of difficulty hiring and retaining a good Phd level experimentalist (although he had some really excellent technicians). He was aware that this was a problem, and he told me that. In his view, the job of the experimentalist was to check his (Dr. Bussard’s) theories. That sociology doesn’t go over very well with experimentalists. In my view, having a good, experienced experimentalist is absolutely essential. We now have that at EMC2, and in fact Dr. Park and our technicians are the ones who should be credited for getting the WB-7 operating and producing meaningful results on such a short timescale. When we go into the laboratory, they call the shots, I don’t.

I would also like to comment on the question of simulations vs. experiments. I spent most of my career doing 3-D nonlinear MHD simulations in both CTR Division and T Division at LANL. In plasma physics, simulations are only as good as the questions you ask of them. They can provide good guidance, but there is usually a huge difference between virtual reality and reality reality. Simulations and experiments have to go hand-in-hand. If you rely too heavily on computations you end up building yourself a house of cards. Usually, the issues that you anticipate with the calculations aren’t the ones you encounter in the laboratory.

Finally, a few words about FRCs. I was at LANL when the FRX-A, FRX-B and FRX-C devices operated. As I’m sure Art knows, they also have issues like tilt modes in the large S limit, m=2 rotational modes if you throw away the cusp stabilization (like the MTF people are doing), the problems with high voltage repetitive pulsed power, steady-state formation and sustainment without opening up the flux surfaces, and large fluctuations which contribute to the transport. That being said, I think FRCs are a good idea. However, there isn’t a snowball’s chance in hades that the DOE is ever going to support these concepts at the level they need to be supported in order to make significant progress. These people need to be looking at other sources of funding, and if they want to do that then they are going to have to come up with a REALLY attractive vision for their final product. They can’t afford to be conservative. The Tri-Alpha people understand this, and the rest of the FRC folks need to wake up to it. In this world, whether or not you can make something work is irrelevant if you don’t have an attractive final product.

Aero
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Post by Aero »

Yes. I think all of us who have lived through the Microsoft Windows life cycle understand exactly what you mean. Sell the promise. Or maybe its, "Sell the sizzle, not the steak!"
Last edited by Aero on Sat Jul 12, 2008 8:54 pm, edited 2 times in total.
Aero

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