What does Maxewllian mean?

[Art Carlson]

I have never seen more than hand-waving from the anti-maxwellian faction, so I couldn't even say whether, under their assumptions, a non-maxwellian distribution is reasonable, and if it is, whether that will make a difference.

Since Rick was involved in POPS, resonance phenomena might be a good start...

A good start for who to do what?

No polywell that has been built or proposed has been driven periodically, so POPS is not relevant to the question of whether or not the velocity distributions in a polywell are maxwellian.

[MSimon]

A good start for who to do what?

Increase the compression ratio.

[D Tibbets]

...To maintain a non-maxwellian distribution will require electrons to be removed at one energy and replaced at another energy. At least one of those populations of electrons will have to have an energy near E_e... [/b]

Isn't that percisely what occurs in the Polywell? The electrons are acellerated by the pos magrid to ~ 12,000 eV, to provide an internal well depth of ~ 10,000eV (WB6 example). They will bounce around inside, tending to thermalize with time, but the lifetime is less than the thermalization time (relaxation time?). Befor they can thermalize fully they escape the system through a cusp, and are replaced by new mono-energetic electrons (12,000 eV). I have heard R. Busard comment that the speed of the electrons are ~ 1 billion cm per second (is that appropiate for 10,000-12,000 eV?). Is this the injection speed or the average speed? I'll assume it is the injection speed and that the average speed is ~ 1/2 this (assuming the electrons slow to low speeds as they pass through the center, then acellerate again due to mutual repulsion). Also, I have seen comments that the life time of an electron is ~ 100,000 passes or orbits befor escaping. I'm guessing that the escaping electrons are mostly cusp losses- ie they escape to the vacuum vessel wall as opposed to electrons that hit the magnet wall (diffusion?). If some percentage is recovered by recirculation then their reentry speed would be the same as the original- 12,000 eV due to the charge on the pos magrid. The escaping electrons may be faster than the injection speed and hit the wall, or they may be the same or slower speed, and recirculate/ reenter the magrid at the original 12,000 eV (reset to the original speed - I'm thinking that the terminal speed will be almost the same weather the electrons start their return journey 1 mm from the magrid, or several cm from the magrid)*.

Based on the assumptions of average electron speeds of 500,000,000 cm/s , 30 cm wide Wiffleball (larger than possible with 30 cm wide coil spacing), and 100,000 transits befor loss to the vessel wall (if this includes recirculated electrons that had been reset to the original speed, it would be even better); the average life time would be ~ 5 ms. The article I referenced above stated they were maintaining non Maxwellian distributions of the electrons in their system for 25-30 ms, so 5 ms lifetimes in the WB6 is comfortably within this limit (assumeing there is any correlation between the systems).

If confinemet times are even less due to greater than advertised cusp leaking, the time for the electrons to thermalize would be even less (at the cost of needing more electron gun provided new electrons).

* There were two ways of acellerating the original electrons mentioned by Dr Bussard. Either have the electron gun at high neg voltage with the magrid grounded, or have the electron gun at low voltage and the Magrid at high pos voltage. The diffinative experments (if you let me use that term) were done with the Magrid at high pos voltage. This is what my arguments are based on. Would a neutral grid (same potential as the vacuum vessel) possibly change the dynamics of the recirculating electrons, along with the escaping ions?


Dan Tibbets

[Art Carlson]

...To maintain a non-maxwellian distribution will require electrons to be removed at one energy and replaced at another energy. At least one of those populations of electrons will have to have an energy near E_e... [/b]

Isn't that percisely what occurs in the Polywell? The electrons are acellerated by the pos magrid to ~ 12,000 eV, to provide an internal well depth of ~ 10,000eV (WB6 example). They will bounce around inside, tending to thermalize with time, but the lifetime is less than the thermalization time (relaxation time?). Befor they can thermalize fully they escape the system through a cusp, and are replaced by new mono-energetic electrons (12,000 eV).

Right. This is the way Nebel looks at it and it is definitely one way - perhaps the easiest way - to maintain a non-maxwellian distribution.

The trouble is that pouring electrons in and letting them run out costs power. I showed above that the simplest model, where the electrons take most of their hard-won energy with them when they leave, can only work at energies above 3 MeV. You don't want to go there, for reason we could discuss. A better way to look at the numbers might be to fix E_e at 10 to 20 keV and look at the times involved. If we assume that when an electron passes through the system, it loses a fraction f of the energy E_e, then we can show that f has to be less than about 1/2400 for practical D-T fusion. In other words, your set-up has to recover 99.96% of the energy your accelerator gives to your electrons. (We've only talked about physics so far, but you have a technological problem too: Your direct conversion of fusion power to electrical power needs to be 99.96% efficient, too.)

If the number itself doesn't scare you, we could go into details about why you can't do it. If you inject electrons at an energy E_e and siphon them off at E_e*(1+f), then you have a steep gradient in the distribution in velocity space. This will make the time scale for relaxation of the distribution even shorter than the value I used.

Your own calculation pretty much misses the point on two counts. For one, it doesn't address the question of the value needed for the Lawson product.

The other is that the paper you site actually confirms my calculation. They measure a significant change in the distribution on a time scale not much shorter than the electron collision time they calculate using the same formula I use. The reason they deal with milliseconds is that they have a wimpy plasma, only 3e9 cm^-3.

[scareduck]

Prejudice based on limited experience. Politics, not Science.

"Extraordinary claims require extraordinary proof" is the operating principle here. It's not prejudice, it's called requiring the people making the claims to back them up with actual data.

[MSimon]

What does Maxwellian mean? Smart. Agent Smart. Agent 86.

Use: That was a Maxwellian thing to do.

==

I'm sorry. I couldn't help myself.

[TallDave]

I have never seen more than hand-waving from the anti-maxwellian faction

Well, there's also the Chacon paper. The full bounce-averaged Fokker-Planck model should be closest to accurate.

The trouble is that pouring electrons in and letting them run out costs power.

Should be 5-10MW for a 100MW reactor.

In other words, your set-up has to recover 99.96% of the energy your accelerator gives to your electrons.

Huh? Why? Shouldn't that depend on the size and density of the plasma?

Does the Lawson criterion really make sense applied that way to a Polywell? There is no ignition temperature as Polywells require constant input, and we get energy from neutrons with no concern over whether they keep the plasma hot (since we don't care about ignition). It looks like you're assuming a flat, neutral distribution (i.e. no well, no ion focus).

[KitemanSA]

Don't be a luser:
http://www.catb.org/~esr/faqs/smart-que ... disclaimer
Good advice for all noobies on any discussion board.

Good advice, but it would also be nice to have a technical FAQ section that would have most of the directly relevant info easily to hand.

[MSimon]

Don't be a luser:
http://www.catb.org/~esr/faqs/smart-que ... disclaimer
Good advice for all noobies on any discussion board.

Good advice, but it would also be nice to have a technical FAQ section that would have most of the directly relevant info easily to hand.

If you want to write one have at it. I can put it up as a sticky and lock the thread (I think).

If you just made a list of of questions that would be a start.

[alexjrgreen]

Prejudice based on limited experience. Politics, not Science.

"Extraordinary claims require extraordinary proof" is the operating principle here. It's not prejudice, it's called requiring the people making the claims to back them up with actual data.

Take care when quoting Marcello Truzzi. He was very critical of people who determined the validity of a claim prior to investigation.

In science, the burden of proof falls upon the claimant; and the more extraordinary a claim, the heavier is the burden of proof demanded. The true skeptic takes an agnostic position, one that says the claim is not proved rather than disproved. He asserts that the claimant has not borne the burden of proof and that science must continue to build its cognitive map of reality without incorporating the extraordinary claim as a new "fact." Since the true skeptic does not assert a claim, he has no burden to prove anything. He just goes on using the established theories of "conventional science" as usual. But if a critic asserts that there is evidence for disproof, that he has a negative hypothesis --saying, for instance, that a seeming psi result was actually due to an artifact--he is making a claim and therefore also has to bear a burden of proof.

Marcello Truzzi, On Pseudo-Skepticism, Zetetic Scholar, 12/13, pp3-4, 1987

In Science, any claim requires proof. Treating claims that support the status quo more favourably than those that don't is just politics.

[KitemanSA]

Don't be a luser:
http://www.catb.org/~esr/faqs/smart-que ... disclaimer
Good advice for all noobies on any discussion board.

Good advice, but it would also be nice to have a technical FAQ section that would have most of the directly relevant info easily to hand.

If you want to write one have at it. I can put it up as a sticky and lock the thread (I think).
If you just made a list of of questions that would be a start.

I have asked our esteemed aminitrator to start a F.A.Q. forum in the Technical Group and allow me (and others if desired) to moderate it so that I could do that very thing. I believe that a F.A.Q. Forum is the best place to put such stickies. Folks would know to look there.

[Betruger]

It's not status quo or politically motivated to do the math and see that the polywell doesn't make sense on paper..

[alexjrgreen]

It's not status quo or politically motivated to do the math and see that the polywell doesn't make sense on paper..

Tout d'abord poussé par ce qui fait en aviation, j'ai appliqué aux insectes les lois de la résistance de l'air, et je suis arrivé avec M. SAINTE-LAGUE a cette conclusion que leur vol est impossible.

Antoine Magnan, 1934 "Le Vol des Insectes" - Introduction

[Betruger]

That interdisciplinary leap isn't comparable to what Dr Carlson is doing. Another example: I think the Polywell isn't as Dr Carlson models it, or Dr Nebel wouldn't disagree as he does. And yet I see that Dr Carlson's arguments are valid. Nothing motivated by status quo or even politics. Our case is special: we have no data to go by. Unless someone can somehow divine the theory that ties these two loose ends together, the only rational way to go anywhere is a "classic" physics approach.

[alexjrgreen]

I'm sorry. I couldn't help myself.

Just a momentary loss of CONTROL. Quite understandable...