ICC 2011

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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KitemanSA
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Post by KitemanSA »

Joseph Chikva wrote:
At the dead center no tangential scattering would be possible.
“Annealing” as I understand only equalizes the temperatures in all points of plasma. And in result temperature will be uniformly high everywhere.
This is not my understanding.
Annealing is the process of NARROWING the velocity spread at a LOW energy; at the center for electrons, at the edge for ions. Thus you wind up with a universally LOW spread (temperature) on a universally HIGH monotonic energy distribution equal to about .8 of the MaGrid voltage for the ions.

As an aside, why would off center impacts for D + D having the same velocity at the core cause a distribution of energy? Since the particles are the same size, shouldn't the outgoing values of "speed" be the same as the incoming? Hmmm.

KitemanSA
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Post by KitemanSA »

Joseph Chikva wrote:
KitemanSA wrote:Annealing. This is the expected process to return some, if not all, of the tangential motion into radial.
Absolutely wrong. As electrostatic attraction by virtual cathode acts only radially and stopping the particle only in radial direction, can not nor accelerate or decelerate tangential velocity.
This is a non-sequitur since I never stated nor implied that the electro-static attraction had any effect in accelerating or decellerating TANGENTIAL velocity.
Joseph Chikva wrote:Collisions can only randomize the velocity and can not reduce them.
I think you will find that this is not true. Collisions between ions tend to "Maxwellianize" their distribution which will bring a velocity distribution that is GREATER than normal back toward the normal. But that NORMAL is defined by the instantaneous values of velocity in the local area. So, if you have removed a large part of an ion's TOTAL velocity by that electrostatic attraction you mentioned, you are left with a distribution WIDER than the Maxwellian" for the local ion population. Then the velocities will relax toward the norm and become a LESSER spread than before. Annealing.

rcain
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Post by rcain »

hello again JC,

Still battering this old chesnut I see. If Kiteman cannot explain it to you and you cannot visualize what is happening by now, then god help us all. ;)

To be fair however, I believe I do understand the point you are trying to make, and you are not completely wrong. (IMO).

By my own limited understanding, some points which may help clarify:

1) Neglecting any nuclear reactions for the time being, the only kinetic energy into the system, so far as any particles are concerned, is the 'impulse' imparted to the ions (/electrons) at initial injection into the system. This is in a (generally) radial direction.

2) The only potential energy in the system is established by the central (virtual) cathode (wrt injected ions).

3) The system can be considered as a harmonic oscillator, with a periodic exchange between potential energy and kinetic energy of any/each or the particles within it. What is 'tangential momentum' at one point in any particles trajectory about the system, becomes 'radial momentum' at pi/2 rads later in its orbit. Then vice versa. (Hence Kiteman's point on 1.5d dimensionality).

4) Most collisions in the system are considered 'elastic' or semi-elastic.

5) The main (only) loses from the system, are:
a) Bremsstrahlung (as you correctly state)
b) Particles (and their energy) lost/expelled from the system due to upscattering - in and around the core, and importantly from the outer edge region ('boiling off'/annealing). Particle loss is possibly the most important mechanism in mitigating the phenomenon you are trying to describe. (Although Brem may also become very significant at larger scale/energy levels).

6) Collision energies within the system are not 'rectified' in any way (as you correctly point out). (Though losses from the system are, by their very nature).

Thus, what I see, is an 'average' set of 'displacements' of 'ideal' elliptical orbits around the central core region (that is: statistically, many/most orbits will pass either side of the geometric centre of the device, by an amount related to the average 'thermalisation' (or net tangential component of velocity caused by collisions within the system).

This means that statistically I would expect an 'inner shell' of highest density, rather than a simple point centre.

Most importantly, is the aspect of average 'lifetime' of particles in the system. This is, by design, kept to be less than the overall critical thermalisation time of the system as a whole. (for the very reasons you (correctly) posit).

Polywell can only operate effectively within a very highly tuned regime. Outside of this, and as you say, the system becomes dominated by chaos.

Does this make sense to you?

Joseph Chikva
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Post by Joseph Chikva »

rcain wrote:Does this make sense to you?
Considering motion in Polywell as addition of two motions: harmonic oscilation and thermal chaotic yes, that makes sense.

Joseph Chikva
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Post by Joseph Chikva »

KitemanSA wrote:This is not my understanding.
That is my understanding on base of have read statements of 93143 (I am sorry if I remember this nick incorrectly)

KitemanSA
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Post by KitemanSA »

Joseph Chikva wrote:
KitemanSA wrote:This is not my understanding.
That is my understanding on base of have read statements of 93143 (I am sorry if I remember this nick incorrectly)
Well I guess you and Mr. Numbers have to improve your understanding. :)

Joseph Chikva
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Post by Joseph Chikva »

KitemanSA wrote:Well I guess you and Mr. Numbers have to improve your understanding. :)
May be.

hanelyp
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Post by hanelyp »

KitemanSA wrote:As an aside, why would off center impacts for D + D having the same velocity at the core cause a distribution of energy? Since the particles are the same size, shouldn't the outgoing values of "speed" be the same as the incoming? Hmmm.
Picture two particles speeding towards a common point, one slightly ahead of the other such that it is at the point the paths intersect as the second hits it. In this rare worst case collision the second particle comes to a stop sending the first off at twice the energy.

93143
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Post by 93143 »

KitemanSA wrote:
Joseph Chikva wrote:
KitemanSA wrote: This is not my understanding.
Annealing is the process of NARROWING the velocity spread at a LOW energy; at the center for electrons, at the edge for ions. Thus you wind up with a universally LOW spread (temperature) on a universally HIGH monotonic energy distribution equal to about .8 of the MaGrid voltage for the ions.
That is my understanding on base of have read statements of 93143 (I am sorry if I remember this nick incorrectly)
Well I guess you and Mr. Numbers have to improve your understanding. :)
Uh, yeah. I'm not sure how Joseph Chikva has arrived at the conclusion he has, but it's not what I said. It's not even closely related to what I said.

What I said was more or less what everyone else here has been saying - that annealing is supposed to be a collisional process that occurs due to the difference in particle energy/density/residence time between different regions of the plasma, and slows down global thermalization, preventing the initially ordered radial motion of the particles from breaking down into chaotic thermal motion faster than fusion and particle loss require the plasma to be replaced.

...

Also, regarding angular velocity, there is an effect in a Polywell that should prevent it from getting out of hand. Say you have particles that have passed through the core region and thermalized somewhat, picking up some angular velocity in the process. The ratio between radial and angular velocities decreases as they slow down near the largest radius they can reach, becoming zero as they stop (radially) to turn around. On average, the result of this is an anisotropic distribution, where angular velocities near the edge are higher than radial velocities. Simple thermalization will then tend to transfer angular energy to the radial direction.
As an aside, why would off center impacts for D + D having the same velocity at the core cause a distribution of energy? Since the particles are the same size, shouldn't the outgoing values of "speed" be the same as the incoming? Hmmm.
No.

Take, as an example, two frictionless hard spheres at equal velocities encountering one another at a 90° angle. If the axis of impact is 45° from each initial velocity vector, speed is conserved. If, however, it is 90° from one and 0° from the other (a T-bone collision), the T-boned particle will head off at a 45° angle with twice the kinetic energy (1.41 times the speed), and the other particle will stop dead.

EDIT: Yeah, just like hanleyp said.

Coulomb collisions generally aren't quite that dramatic, but the general principle applies; the particles have to be pretty precisely lined up for speed to be conserved.

If what you said were true, a monoenergetic distribution could never thermalize.

Joseph Chikva
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Post by Joseph Chikva »

93143 wrote:Uh, yeah. I'm not sure how Joseph Chikva has arrived at the conclusion he has,...

What I said was more or less what everyone else here has been saying - that annealing is supposed to be a collisional process that occurs due to the difference in particle energy/density/residence time between different regions of the plasma, and slows down global thermalization, ...
From your statement that I have bolded
If we have media with local overheating and also we have a vigorous mass transfer in it, in result we will get the tendency to equalization of temperatures in all points.
But at the same time I am not sure about slowing of thermalization. As thermalization/cooling depends only about balance between input and output energies. Temperature can be uniform or not uniform. Multiple collisions and mass transfer are the factors to make temperature uniform (temperate gradient equal to zero or near zero) but energy input from the accelerating field and multiple collisions make their job - heating plasma.
93143 wrote:If what you said were true, a monoenergetic distribution could never thermalize.
If "monoenergetic", so, no distribution. Or no?
And why can not thermalize? Example: injection of neutral atoms into TOKAMAK. Do those atoms not thermalize?

93143
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Post by 93143 »

Joseph Chikva wrote:
93143 wrote:What I said was more or less what everyone else here has been saying - that annealing is supposed to be a collisional process that occurs due to the difference in particle energy/density/residence time between different regions of the plasma, and slows down global thermalization, ...
From your statement that I have bolded
If we have media with local overheating and also we have a vigorous mass transfer in it, in result we will get the tendency to equalization of temperatures in all points.
No, the effect I am describing is not heat transfer. It is due to a difference in collisionality, that depends (via cross section) on the particle kinetic energy, which of course varies in space due to the electrostatic field. This variance of kinetic energy also results in differences in density and residence time, and the result is that thermalization at low relative particle speed dominates over thermalization at high relative particle speed, which slows global thermalization in terms of the average particle kinetic energy.

Since the energy difference I'm talking about is not a thermal energy difference, but an electrostatic potential well (resulting in a gradient in ordered radial kinetic energy but not in total particle energy), it doesn't result in heat transfer.

If you consider the temperature as only the average chaotic deviation of energies from the ideal monoenergetic/bimodal case, then I suppose you could consider annealing something related to heat transfer, and of course some heat transfer will occur - but since annealing is a non-LTE effect, simply thinking of it in terms of heat and temperature is very misleading.

...

The particles in the plasma are lost at a certain rate - electrons by leakage, and ions by fusion (and upscattering, but since that cools the plasma it may be undesirable as a significant loss mechanism unless it can be countered with RF excitation or some such). In steady-state operation, the injection of new particles would match this loss rate, and if the theory of operation is correct, the plasma should thermalize (globally) more slowly than it is replaced. This results in an equilibrium condition that is highly non-Maxwellian over most of the plasma volume.
93143 wrote:If what you said were true, a monoenergetic distribution could never thermalize.
If "monoenergetic", so, no distribution. Or no?
The word "distribution" simply refers to the probability function in velocity space. A Dirac delta is still a distribution. In this case I meant more of a Dirac sphere, where all particles have the same speed but in random directions.
And why can not thermalize? Example: injection of neutral atoms into TOKAMAK. Do those atoms not thermalize?
Check the bolded text. I was responding to an idea that was wrong, and one way it can be seen to be wrong is to consider that it makes an unphysical prediction - ie: that a monoenergetic isotropic plasma does not thermalize.

We know that a monoenergetic isotropic plasma does thermalize; therefore there must be something wrong with KitemanSA's idea. (Of course, hanleyp and I had already demonstrated this to be so with an example...)

Joseph Chikva
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Post by Joseph Chikva »

Yes, I am considering
the temperature as only the average chaotic deviation of energies
As this is classic definition - measure of average energy of chaotic motion.
I do not understand what advantage gives to go aside from this definition.
And it is easier for me to consider total motion in Polywell as addition of two types of motion: harmonic oscillation and chaotic thermal.
I never thought about influence of externally applied field on thermal distribution. Think that it will not be Maxwellian.
Also think that "annealing" is not a trick for achievement of some purposes (slowering of thermalization) but that is feature of Polywell. As at given dimensions, number of injected particles, electric field intensity, etc. you will not have ability to change "collisionality" but will get its certain value.

KitemanSA
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Post by KitemanSA »

hanelyp wrote:
KitemanSA wrote:As an aside, why would off center impacts for D + D having the same velocity at the core cause a distribution of energy? Since the particles are the same size, shouldn't the outgoing values of "speed" be the same as the incoming? Hmmm.
Picture two particles speeding towards a common point, one slightly ahead of the other such that it is at the point the paths intersect as the second hits it. In this rare worst case collision the second particle comes to a stop sending the first off at twice the energy.
As far as I can tell, momentum won't allow that to happen. BOTH momentum AND energy must be conserved, and in order to conserve momentum, the second would need twice the velocity. That is FOUR times the energy. That extra energy is NOT available. Remember, the assumption is that all particles START with the same energy and momentum magnitude. How do you change that?

I accept that IF there is a slow ion in the way of a fast ion, the momenta and energies can be rearanged. But I don't see it with all particles STARTING with equal energy. HMMM.

93143
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Post by 93143 »

Joseph Chikva wrote:Also think that "annealing" is not a trick for achievement of some purposes (slowering of thermalization) but that is feature of Polywell. As at given dimensions, number of injected particles, electric field intensity, etc. you will not have ability to change "collisionality" but will get its certain value.
Right. If it works, it's not something you do to a Polywell; it's just something that happens in a Polywell. You may have to get the operating parameters tuned properly for it to work right, but once you've done that, annealing just happens on its own (supposedly).

@KitemanSA:The particles in our example are moving at 90° from one another. Remember what happens when you have two equal components of momentum at right angles? Twice the energy, sqrt(2) times the speed, at 45°.

Or you could draw some free-body diagrams and actually do the problem.

You are making a mistake. I very nearly made a fool of myself on a public forum (possibly fusor.net) a few years back with the same mistake (as I recall, I had been on the verge of belittling my opponent's intelligence when I figured it out).

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