What does Maxewllian mean?

[Robthebob]

Sorry for being such a college student and not know anything, I'm not worthy, but what does maxwellian mean?

Like maxwellian plasma, maxwellian electron confinement, etc...

[Betruger]

I'm no physicist, but from what I've read on the forum and in linked articles, Maxwellian distribution seems to be a very common (if not the most common) category. So you could easily infer that it ought to be an easy concept to find explained on the usual learning resources on the internet. Such as wikipedia, hyperphysics, wolfram physics. I could be wrong on what Maxwellian refers to, but I reckon it's as easy to find as the 30 seconds of googling/clicking I've just spent.
One of the things you must show when asking for elders' and peers' help is willingness to make effort to learn on your own, e.g. that you've exhausted what you already have at your disposal before asking for someone to help out. Otherwise (and I'm not implying you, just arguing this principle) people they tend to think you intend to be spoonfed. And that never works out

And it's a bit derogatory to say you're throwing your life away for "this fusion mess". It comes off as low self-esteem. With all due respect
Good luck...

[Art Carlson]

Pertaining to particles whose velocities are described by a Maxwell–Boltzmann distribution. (But I second Betruger: If you want to know something, check Wikipedia first. You can google if you'd rather, but Google's first link, as in this case, is almost always to Wikipedia.)

[KitemanSA]

So I presume, having been suitably chastened and having gone to wikipedia or elsewhere, you have determined that "Maxwellian" ~ "thermal", which Polywell is NOT.

[Art Carlson]

So I presume, having been suitably chastened and having gone to wikipedia or elsewhere, you have determined that "Maxwellian" ~ "thermal", which Polywell is NOT.

So they say. Do we have any experimental evidence for that? How about robust theoretical arguments? I think both are pretty thin.

[KitemanSA]

So they say. Do we have any experimental evidence for that? How about robust theoretical arguments? I think both are pretty thin.

Noted. Perhaps I should have said "Which Polywell is, in theory, NOT." Better? If it is Maxwellian, most folks would conclude it won't work. However, the data that IS at hand, limited though it is, is consistant with that theory; unless you think the Drs B&N are fools or liars.

[D Tibbets]

So they say. Do we have any experimental evidence for that? How about robust theoretical arguments? I think both are pretty thin.

At least in a Penning trap type devise, see:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD ... tTRDoc.pdf


Dan Tibbets

[D Tibbets]

Sorry for being such a college student and not know anything, I'm not worthy, but what does maxwellian mean?

Like maxwellian plasma, maxwellian electron confinement, etc...

Hopefully, I'll not confuse you, but I understand that Maxwellian distributions are predictable spreads of energy/temp/ speed in a population of particles (in this case based on the mean temperature). Think of black body radiation, Bell curves, incandesent light bulbs, incandesent gases like the sun, plasma in a Tokamak. Also, think of standard deviation in a population, weather you're talking about energy, response to a drug, etc. Examples of non Maxwellian distribution of particles would be lasers, photoelectric effect, absorption and emission spectra, flourescent light bulbs (emission spectra). The intermediate conditions presumably could occur, narrower distribution, the peak or mean [edit-probably should say average, not mean] skewed to one side or another, etc.

My assumption (hope?) is that the Polywell falls into this catagory. It is not percisely monoenergetic like a laser, but the distribution (spread) in the electron energy, etc is significantly less than that predicted by Maxwellian assumptions. Thus, using equations that assume a Maxwellian distribution need to be modified to be acurate.

A fuser (like the Polywell) is basically a spherical arrangement of many linier acceleraters. A charged partical is acellerated by an electric field. In isolation the terminal velocity of the particles would be over a very narrow range (non Maxwellian distribution). But, as they interact with other charged particles, etc. they assume a Maxwillian distribution. The key is how fast this occurs and what can happen to the particles befor they reach this Maxwellian state.

At least that is my take on the situation...

Dan Tibbets

[MSimon]

Don't be a luser:

http://www.catb.org/~esr/faqs/smart-que ... disclaimer

Good advice for all noobies on any discussion board.

[imaginatium]

So I presume, having been suitably chastened and having gone to wikipedia or elsewhere, you have determined that "Maxwellian" ~ "thermal", which Polywell is NOT.

So they say. Do we have any experimental evidence for that? How about robust theoretical arguments? I think both are pretty thin.

Art,you keep claiming lack of evidence for the polywell being non Maxwellian. Well, what experimental evidence do you have, that it is Maxwellian? And, in the lack of evidence, what justification do you have, for asserting that, it is more resonable to assume that the polywell is Maxwellian (which no one who has seen the data claims), than to assume that it isn't (As Bussard, Nebel, and everyone else associated with the polywell have stated).

[Betruger]

He has no experimental evidence. It's a case of burden of proof, that plays against the Polywell until evidence is shown that it is indeed an exception to the rule.

[alexjrgreen]

He has no experimental evidence. It's a case of burden of proof, that plays against the Polywell until evidence is shown that it is indeed an exception to the rule.

Prejudice based on limited experience. Politics, not Science.

When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.

Arthur C. Clarke "Hazards of Prophecy: The Failure of Imagination"
Profiles of the Future (1962).

Experience with tokamaks and magnetic mirrors doesn't necessarily trump experience with beam power tubes...

[Betruger]

I don't remember Dr Carlson ever saying the Polywell as Dr Bussard & co report it is impossible. Burden of proof is required for any exception to any rule. The rule in the Polywell's case is physics.. Dr Carlson has so far the most theoretical evidence that the Polywell can't work as modeled.

I'm not taking any sides, I'm just taking things at face value. The Polywell as Dr Carlson has modeled it (and hasn't yet been refuted) can't work. And yet from everything we've seen so far, the WB7 is working. Those are the facts. How they tie together is anyone's guess. I'd say the Polywell isn't as Dr Carlson models it. That this is a fact and why it is different can only be figured out by either finding a better alternative to Dr Carlson's models, or by seeing the experimental evidence and infering such an alternative from it.

Like I said, I'm not taking any side. My gut feeling is that the Polywell isn't as Dr Carlson envisions it. Somewhere between theoretical premise and practical implementation there's a fork in the road between what ought to happen (as Dr Carlson argues) and what really happens. Which is very curious, because he has the strongest, most precise grasp of the physics (from what I've read on the forum). Something very interesting is going on in that vacuum chamber.

[Art Carlson]

The Polywell as Dr Carlson has modeled it (and hasn't yet been refuted) can't work. And yet from everything we've seen so far, the WB7 is working. Those are the facts.

Just what have we seen so far? There have been some vague statements, but I have not seen any experimental results that would refute my model.

Art,you keep claiming lack of evidence for the polywell being non Maxwellian. Well, what experimental evidence do you have, that it is Maxwellian? And, in the lack of evidence, what justification do you have, for asserting that, it is more resonable to assume that the polywell is Maxwellian (which no one who has seen the data claims), than to assume that it isn't (As Bussard, Nebel, and everyone else associated with the polywell have stated).

As far as I know, nobody has ever measured the electron or ion distributions in a polywell. To answer the question of what is more likely, you have to make some quantitative estimates. The simplest estimates will involve a number of assumptions that might be under dispute.

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.

The simplest estimate we can make goes like this. The characteristic collision rate for electrons is

• nu_e = (2.9e-12 s^-1)*(n/m^-3)*Lambda*(E_e/eV)^-1.5

The Coulomb logarithm Lambda = 10. E_e is a typical electron energy. If the electrons are maxwellian, then E_e=T_e. Note that the relaxation is faster for low energy electrons, so no one should object if we take E_e to be near the required well depth, say E_e=(1e4 eV).

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, so it is reasonable to take E_e*n*nu_e to estimate a lower limit on the power loss per unit volume. In other words,

• tau_E = (E_e*n)/(P_loss/V) < (E_e*n)/(E_e*n*nu_e) = nu_e^-1

Many years ago, Lawson calculated for us that, for a plasma producing useful energy from the D-T reaction,

• n*tau_E > 1.5e20 s/m^3

From this we can require

• 1.5e20 s/m^3 < n/nu_e = n / [ (2.9e-12 s^-1)*(n/m^-3)*10*(E_e/eV)^-1.5 ]

This gives us a lower limit on the electron energy:

• E_e > 2.7 MeV

That's a factor of 100 too high, so the conclusion (once you all have checked my math) is robust: Until we have a good reason to think otherwise, it is most reasonable to expect the electrons to be nearly maxwellian.

[alexjrgreen]

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...