Debye Length

[MSimon]

And except for the loss equations

minor detail those loss equations lol .... hey why not just go ahead and build a plethora of them if its as easy as you are suggesting?

When there's huge holes in your theory and no evident attempt to plug them, or refute challenges, it smells like scam and failure ... just saying, no accusations.

Let me add that there are physicists I trust who believe it can be made to work. And others of equal stature who say it can't.

My attitude (since Nov of 2006) is simple - since it is disputed - do the experiment.

Nick Krall is a Polywell fan. Not exactly a slouch in the plasma physics realm.

[icarus]

MSimon:

I'm working on it.

I truly admire your faith and tenacity.

There are still some huge leaps involved with this thing and Murphy's law will not be cheated though, so you better have your numbers stacking up ( I suspect you already know this), before you blow meaningful resources.

What confuses the heck out of me is the point blank refusal to tap the essentially free resources of the wider theoretical science community. Good challenging questions are as useful as good answers, all free.

[TallDave]

TallDave

Anyways, equations probably aren't good enough to model overall behavior of the system,

You are plain wrong. Do you truly believe there are no equations to model this system, as in, there is some new phenomena going on that has no basis in current physics?

Physics without equations is pretty limited, but engineering is impossible.

If this thing works, a set of simple first order equations describing overall behavior of it will be arrived at in short order by the huge mathematical/physics community. As it stands, there are a few guys tinkering around in isolation. It will die on the vine without a broad spectrum of theoretical discussion, an essentially free input also. An incomprehensibly short-sighted, insular bunker-mentality holds sway.

Heh, slow down and exercise a little reading comprehension, icarus. I didn't say there were no equations or any new physics, I said a simple equation was insufficient to model the system, especially in terms of how it might organize into concentric Debye sheaths, to answer some of these questions like "How will losses scale?" Yes, once we know how the system behaves a variety of simple equations could describe various aspects of it, but that's putting the cart well before the horse. Most of the discussion here has circled around what qualities seem possible given what we know.

Are you looking for a loss equation derived from simulation? Joel gives one, Bussard gives another, Chacon's bounce-averaged Fokker-Planck looks at it from another angle. If you're asking me what the right loss equation is... well I've been saying for years we need to do the experiment to answer that. WB-8 results will tell us a lot. I do think the correct model will end up looking something like 93143's concentric Debye sheaths, and not like the "everything collapsing into a Debye sheath at the edge" that has also been proposed.

If the "wider theoretical science community" wants to do some more simulations or make criticisms, I don't think anyone objects.

[icarus]

TallDave patronising git said:

Heh, slow down and exercise a little reading comprehension, icarus.

I think I've comprehended the state of affairs quite fine and your answer gives me every confidence I have.

You'll just keep slipping from one grand-standing, empty statement to the next, ad infinitum. It must help make you feel big and important, and that's okay, but the bottom line is you have very little, if anything, to offer that isn't already known and very little to offer, on a lot that already is.

Thanks for your time anyway. And don't bother with building that simulation ... . Go ahead with the usual speculate, obfuscate, rinse and repeat cycle.

Theory eh? hehehehehe, yeah right.

[TallDave]

Well, if you refuse to understand the difference between an equation derived from model and the model itself, I can't help you.

I'm not trying to "offer" anything, I'm trying to understand and share. I pointed you to three simulations and two loss equations and all you've done is whine. If you're representing the "wider theoretical science community," then I'm disappointed they can't do better than namecalling and complaining. I suggest you pull cranium from posterior, realize Polywell isn't about anyone's ego, and discuss some actual physics. Some of us are busy.

[TallDave]

Speaking of Debye -- I think Tom is right about WB-6, but with WB-8 we're getting nearer reactor conditions. It might be useful to make some predictions of what (if anything) Debye screening will mean for WB-8 measurements, in terms of fusion power and losses, as a basis for judging the competing models of PW behavior.

Do we all agree, as a starting point, that WB-8 specs are .8T and 30cm radius (8x and 2x the respective WB-6/7 measurements)? I know we had a discussion of this, I think that's where we ended up.

I'll have to go back and look at Joel's first simulation again, I think it may have been based on a putative WB-8, so there could be some relevant info there in terms of making predictions about WB-8.

[MSimon]

Go ahead with the usual speculate, obfuscate, rinse and repeat cycle.

My dear boy (and I'm using the snark advisedly) you are the one speculating, obfuscating, rinsing and repeating. Where is your model? What are your assumptions? Do they match reality?

That last question is a real kicker.

I'm raising funds (with some success) to answer the reality question.

Keep sniping all you want. I'll pay it less mind in the future.

Because. You. Got. Nothing.

[TallDave]

If a Polywell were operating in the regime Art Carlson envisions (Debye screening), the characteristic length for the potential well is the Debye length.

But wait - the potential well is about 80-90% of the plasma temperature...

...yeah, it breaks the definition.

This is actually why I think it won't work like Art says; the fact that you've got a bunch of electrons all blazing in one direction, slowing down, increasing their density greatly, and attracting ions from the high-density edge, which then go roaring past them, decreasing their density as they accelerate, and producing (or trying to produce) a net positive charge below the electrons... then what? I think it will form a series of concentric alternating multiple wells, like the layers of an onion - a "polywell", if you will - that averages out to what EMC2's graphs show. Overall the plasma would be quasi-neutral, but locally it would be anything but.

I'm thinking this means we can probably choose an arbitrary well depth within the reasonable range for D-D fusion (i.e. well depth won't affect Debye screening since it's the proportion of the temperature in the well that matters), unless someone has an idea what well depth they're actually operating at...

Well, we can make some educated guesses about the WB-8.1 well depth, I suppose, given that they're attempting p-B11.

[MSimon]

Becoming a Successful Scientist: Strategic Thinking for Scientific Discovery

Don’t read the literature. Graduate students are inevitably told to read the literature to get started. This advice is fine for students, because they are used to looking up the answers in the back of the book anyway and repeating the examples they have seen. For the practicing professional, however, this first step can be inhibiting. First, it channels your thoughts too much into well-worn grooves. Second, a germ of an idea can easily seem insignificant in comparison to finished studies. Third, the sheer volume of material to read may intimidate you into abandoning any work in a new area. Medawar (1967) also advises against reading too much, arguing that study can be a substitute for productive work.

My recommendation for the first step (after getting the germ of an idea) is to put your feet up on the desk and stare out the window. Try to elaborate the idea as much as possible. Do some calculations or quick lab experiments. Write a few pages or sketch out a design. Only after the idea has incubated and developed will it be robust enough to compare it to existing literature. Given a certain level of knowledge in a subject, you know generally what is going on, so you are not likely to be reinventing the wheel. When you go to the literature, you may find that someone has preempted you or that your idea is invalid, but at the risk of only a few days or weeks of work. The cost of good ideas killed off too soon is much higher than the cost of some wasted effort.

I'm willing to waste decades and 10s of millions to get an answer. Definitive. Proved by experiment. Yes/No.

[icarus]

OK. I've. Got. Nothing. (but sniping)

I should "pull my cranium out of my posterior" and "brush up on my reading comprehension" and "stop refusing to understand how equations and models fit together" and "stop whining" and "realize Polywell is not about egos".

Enough said. I've got a lot to work on, it seems like, so I'll leave you to your mutual admiration society, of two, and call it quits here I think.

'Snarkfests' and 'Putdowns' need new topics separate to Theory also, I'd add.

[D Tibbets]

OK. I've. Got. Nothing. (but sniping)

I should "pull my cranium out of my posterior" and "brush up on my reading comprehension" and "stop refusing to understand how equations and models fit together" and "stop whining" and "realize Polywell is not about egos".

Enough said. I've got a lot to work on, it seems like, so I'll leave you to your mutual admiration society, of two, and call it quits here I think.

'Snarkfests' and 'Putdowns' need new topics separate to Theory also, I'd add.

There have been various attacks against the Polywell. I am not in a position to give difinative arguments one way or another. I will coment though that personal attacks does not imprese me . There is a lot of physics, and modeling aviable, mostly from Bussard, etel in the early 1990's. A. Carlson has belittled Bussard as a physicist, and commented that (at least some of) his math is flawed- but he did not spicify details which could be further evaluated. He has made arguments against various aspects of Polywell operation. I don't know the validity of his arguments as he has not defended his positions in detail. When different assumptions are put forward he has ignored them , or at least not worked them. Some of his formulas may be perfectly valid for his assumptions, but the technical jargon and his lack of defining terms has not served to convince me of his perspective. Items which I have not seen addressed is the significance of Debye lengths in high current conditions, non neutral plasma effects on ambipolar aspects, etc, etc.. Perhaps he and others cannot communicate with others not up to his level of technical jargon, or perhaps he just doesn't want to.
In short- if you are going to attack something, do it with detailed arguments (which are no good if they are in a different language).

Sorry for picking on A. Carlson, but he stuck his neck out, without justifying why his contrary assumptions applied. Often valid complaints about the unaviable data, is twisted into proof that there is no data.

If experts disagree, and are unable or unwilling to defend their positions against counter arguments, then who is the audience to trust? As often said, experiment trumps opinion. And, without experimentation/ observation this is all philosophy anyway.

Dan Tibbets

[TallDave]

and call it quits here I think.

If you're not interested in talking physics, please do. Again, busy.

Gettimg back to physics... does anyone disagree with the following assumptions for WB-8:

.8T
30 cm radius
12.5KV drive, hopefully yielding 10K well depth (this is WB-6 conditions which is useful for comparing like to like)

It might be good to flesh out the wiki on things like this. I'm assuming they could run it well in excess of 12.5KV even for D-D -- I know Hirsch went to 150KV in 1967 -- if they wanted to, but I don't know what the hardware limitations would be for their setup. Maybe Simon could say.

[MSimon]

From observation only:

Off the shelf stuff good for 12 KV should be good for up to 50 KV or so. Maybe 75 KV if you pushed the envelope.

[TallDave]

OK, maybe I should go with 18KV drive, 15K well depth. I believe there's wide agreement that 15KV is the optimum D-D temp.

FWIW, here's Rick on what I was trying to convey regarding equations and models

As near as I can tell, the arguments being made here are the same as those made by Rider many years ago. The problem is that you can’t study the polywell physics in isolation, you have to study the system as a whole.
...
5. The devil is in the details. You have to do the energy balance on the entire system to see what will work. Sweeping statements like those made by Rider are overly simplistic.
...
3-D Particle-in-cell is extremely expensive. Resolution goes like (N)**.5 where N is the number of particles. You have multiple timescales and multiple spatial scales to resolve. This means supercomputers.

[KitemanSA]

OK, maybe I should go with 18KV drive, 15K well depth. I believe there's wide agreement that 15KV is the optimum D-D temp.

That is NOT what got inserted into the FAQ on that question. The lowest "optimum" for DD was ~83keV. Even the DT was at about 50. Why is your "optimum" so different, and why didn't you speak up during the FAQ drafting?