We need a new film on YouTube explaining the Polywell.

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

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D Tibbets
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Re: We need a new film on YouTube explaining the Polywell.

Post by D Tibbets »

happyjack27 wrote:ya, no. you said nothing there to explain why ions would prefer one set of radial energies over another; one apsis over another.
Several points. The ions on the edge are not spun up. You could induce this angular momentum in a Wiffleball toy, but this is not what occurs in a Polywell. IF there was a spin up- ions tacking along the Wiffleball edge with a preferred transverse (axial) motion, the plasma would have a dominate flow direction, and this would result in a magnatized plasma, repeatedly denied for the Polywell. Individual ions may assume a high degree of axial motion - approaching a circular orbit instead of a highly parabolic orbit), but these individual axial motions may be in any direction. There is not a preferred direction of rotation. Thus the individual magnetic fields of each ion is cancelled out by ions traveling in the opposite direction.The net plasma induced magnetic field is zero. Compare this to a Tokamak where there is a preferred direction of rotation about the torus and thus a strong and significant magnetic field throughout the plasma.


The ions preferred motion is governed at the simplest level by the potential well. As they fall towards the center- bottom of the potential well, their potential energy in the system is converted to kinetic energy. The ions are fast in the center/ core, intermediate in the mantle and slowing to a stop in the radial vector at the edge. The near spherical geometry has significance. So long as there is some radial component to the ion orbit and there will always be some, then the ion concentration per unit volume will increase towards the center, this is central focus or confluence. The extent of radial contributions is the big argument . Annealing doesn't set the average ion speed at any given radii. The important point of annealing is straight forward thermalization rates that increase rapidly as the average velocity drops in a local area and also includes density considerations. The average radial speed of the ion is determined by the potential well. Annealing is a consequence of normal thermalization (in both radial and angular momentum/ transverse or axial) about a low average speed. The speed will be an average with a bell shaped curve distribution of thermalized energies about this slow speed and this spread might be plus or minus ~ 1000% (as an example). But with an average KE of say 1 eV means that the thermalized KE would be plus or minus 10 eV in this case. This assumes that the ions spend enough time in this edge region that full thermalization occurs. The residence time is greater than the thermalization time. This local condition would always be met if the ions are purely radial, without much thermalization deeper in the machine. Transverse/ axial motion is not effected by the potential well so they would not slow to a stop on the edge due to the potential well, but if their total motion (KE )is small enough in this region they will also fully participate in edge thermalization so their deviation from the average energy spread would also be reduced in the axial direction as well as the radial. The greater the component of axial motion for the ion the less likely it will fully thermalize on each pass through the edge region, thus axial annealing is less absolute than radial annealing. Collisions in the core, mantle and edge are all interrelated. Perhaps the saving grace for the Polywell concerning angular momentum is the spherical geometry with always some radial component (hopefully large component). The collisions will be the greatest in the core because the density is greatest* at least relative to the mantle region. Here angular momentum generating collisions are least significant- all directions from the center is radial. This allows for tailoring of the machine density and energy so that reasonable fusion rates are obtained while the restoring forces of annealing and preferential loss of up scattered ions prevent full ion thermalization in the bulk of the machine, except in the edge region where the average ion energy is modest (sum of radial and transverse KE) with resultant high Coulomb collisionality leading to Maxwellian distributions about a low average energy. This Maxwellian energy spread is proportionately a small fraction of the potential well induced ion energies in the core, thus with each transit from the edge to the core and back again the ion energy is reset to a small energy spread (relative to core energies).

Coulomb collisionality, energy, density and machine size all contribute and gradual thermalization occurs throughout the machine but this is a time dependant process. The edge annealing does not stop global thermalization, but it may slow it so that the ions are lost from containment and/ or fuse first. There is some energy spread but it is much (?) less, especially the problamatic high energy tail.

As I said, the thermalization (radial and axial) of the electrons is a foggier issue, but there may be restoring forces (delaying factors) as well. These are possibly ion tugging towards the center, preferential losses of up scattered electrons and average lifetimes short enough. Here recirculation plays a double dividend. The setup allows for average and upscattered electrons to leave faster than you would otherwise need for energy balance, but because of Magrid direct conversion the energy cost of this shorter confinement time is minimized.

* Coulomb collisionaliy scales as the inverse 1.75 power of the temperature/ KE. This means that at an average energy of say 10 eV at the edge compared to an average energy of 10.000 eV in the core means that Coulomb collisions at the same density occurs 1000^1.75 power more rapidly. That is ~ 60,000 times more rapid, or conversely the MFP is ~ 60,000 times shorter. This needs to be factored with the relative density in the regions as Coulomb collisionality also scales with the density squared. The final result incorporates both. The core may be more dense, but not by a factor of ~ 240, thus if full Maxwellian thermalization occurs anywhere on one pass, it will be in the edge region. This degree of thermalization per pass is the key, so long as the edge thermalization dominates, full ion thermalization deeper in the machine cannot occur.

Um.. to add more considerations, consider that the lifetime of the ion is ended with either escape from confinement or fusion. Fusion results in high energy particles which have KE of perhaps 30 times the KE of the fuel ions. This means the Coulomb collisionality of these fusion ions are 30^1.75 or ~ 500 times less- the MFP is ~ 500 times greater. This means these fusion ions partake in Coulomb collisions much less frequently, they do not share their energy with the fuel ions much before they complete enough passes to find a cusp and escape. This is why a Polywell does not have an ignition condition. The fusion products do not contribute (much) to collisional heating of the plasma They also do not partake in annealing as their speed at the Wiffleball edge is slowed only marginally (like from ~ 3 MeV to 2.9 MeV) by the potential well. Their MFP remains very high and Coulomb collisionality remains very, very small compared to the inter fuel ion collisionality on the potential well edge (or even in the core).

Dan Tibbets
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KitemanSA
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Re: We need a new film on YouTube explaining the Polywell.

Post by KitemanSA »

happyjack27 wrote:ya, no. you said nothing there to explain why ions would prefer one set of radial energies over another; one apsis over another.
Low relative velocities have larger coulomb cross sections that high RVs. Thus, on the way out from the center, faster ions will have a greater tendency to nudge slower ones and normalize (group) their velocities than ions passing each other in/out. Thus, they start the next fall toward center with the same zero velocity and gain the same energy as they fall into the well.

Oh, and ions with TOO much energy leave the well all together. So slower ones get boosted and faster ones leave. Mono-energetic. In theory.

happyjack27
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Re: We need a new film on YouTube explaining the Polywell.

Post by happyjack27 »

KitemanSA wrote:
happyjack27 wrote:ya, no. you said nothing there to explain why ions would prefer one set of radial energies over another; one apsis over another.
Low relative velocities have larger coulomb cross sections that high RVs. Thus, on the way out from the center, faster ions will have a greater tendency to nudge slower ones and normalize (group) their velocities than ions passing each other in/out. Thus, they start the next fall toward center with the same zero velocity and gain the same energy as they fall into the well.

Oh, and ions with TOO much energy leave the well all together. So slower ones get boosted and faster ones leave. Mono-energetic. In theory.
ya,
*faster ones on the way out boost slower ones on the way out, also: (000)
*slower ones on the way out de-boost faster ones on the way out, (001)

*faster ones on the way out de-boost slower ones on the way in, (010)
*slower ones on the way in de-boost faster ones on the way out, (011)

*faster ones on the way in boost slower ones on the way in, (100)
*slower ones on the way in de-boost faster ones on the way in, (101)

*faster ones on the way in de-boost slower ones on the way out, (110)
*slower ones on the way out de-boost faster ones on the way in, (111)

Thermalization. In theory.


and faster ones leave. and new gas is puffed in, introducing ions w/a mix of energy levels.

but then you're saying one's going the same direction spend more time together, so exchange more KE. so it's kind of like separating the "inward" and the "outward" into two separate thermalization regimes. okay, so you still have radial thermalization. you just cross off the (x1x)'s from the list.


to counter-act radial thermalization, you can
* try to ionize at the edges,
* (and conversely de-ionize the low energy ions so they can get to the edges),
* and pump in energy selectively to low-apopsis ions through e.g. RF waves in order to "boost" them. (this, however, is contradictory to de-ionizing low-energy ions)

and to compensate through energy loss in general through high energy ions escaping:
* pump in new ions through neutral gas injection.

but then these things are all energy in, and it might not pay off. if you have to keep pumping energy in to keep it mono-energetic, you have to ask, is it really worth it?

in the long run i see a bunch of cold ions and electrons accumulating in the core, where both magnetic and electric pressure are low. (possibly de-ionizing?) which is fine, actually. you want that to be high density. it's a free density boost.

hanelyp
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Re: We need a new film on YouTube explaining the Polywell.

Post by hanelyp »

Let's consider a simplified 1D model of the polywell plasma. In this we have 4 major particle populations:
:arrow: +X moving ions,
:arrow: -X moving ions,
:arrow: +X moving electrons,
:arrow: -X moving electrons.

Assuming each population starts roughly mono-energetic, each will thermalize more strongly with itself than with the other groups. The 2 ion groups will merge at low energy at the ends of the plasma. The electron groups will merge at low energy at the center.
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happyjack27
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Re: We need a new film on YouTube explaining the Polywell.

Post by happyjack27 »

hanelyp wrote:Let's consider a simplified 1D model of the polywell plasma. In this we have 4 major particle populations:
:arrow: +X moving ions,
:arrow: -X moving ions,
:arrow: +X moving electrons,
:arrow: -X moving electrons.

Assuming each population starts roughly mono-energetic, each will thermalize more strongly with itself than with the other groups. The 2 ion groups will merge at low energy at the ends of the plasma. The electron groups will merge at low energy at the center.
i'm sorry, i'm too distracted by the cool arrow icons... (darn, why didn't i think of that!)

"The 2 ion groups will merge at low energy at the ends of the plasma." - you mean at the apoapsis of their orbits, which is NOT neccessarily at the "ends of the plasma", and the whole point is that they have DIFFERENT apoapsis's; their minimum KE points are at different radii. now what's there to compel ions at their minimum KE, at different radii, to go towards the same radii? nothing that i'm aware of. nothing that anybody has mentioned. and i can think of one thing that ions respond to at low (and esp. minimum!) KE - electrostatic forces. in which case their mutual electrostatic repulsion is probably NOT going to draw them towards the same radius.

happyjack27
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Re: We need a new film on YouTube explaining the Polywell.

Post by happyjack27 »

also, come to think of it, once an ion is inside the wiffleball, it experiences no electrostatic force from the electrons (well, if you think of it discretely, as a hollow sphere, it's really not), but it will experience repulsion from the other ions inside the sphere. so not only will it's trajectory stopped getting warped into the center - it will start getting warped _away_ from the center. i presume this is the virtual anode/cathode inside the virtual other one. (the positive one is inside the negative one.) it's sort of as if the sphere's surface is the true "center" and inside the sphere is sort of a projective reflection. so the peak actually dips in.

and overall it looks like:

Code: Select all

                   negative
   /\/\           ^
\/      \/        | 
 ^magrid       positive
   ^wiffleball
     ^physical center

this of course is undesirable because it decreases both the density and the KE. yet another reason why you want the wiffleball smaller, which is yet another reason why you want high mag field.

now in reality some electrons are going to get tugged in right away to neutralize the center (thousands of times faster than the ions), (since there's no mag field preventing them anymore - they've cancelled it out)

so you get move of a square

Code: Select all

    __           negative
   /   \           ^
\/      \/         | 
 ^magrid       positive
   ^wiffleball
     ^physical center
which means in this region (inside the WB), your ions are going to be purely inertial - they stop "orbiting" for a bit and travel in a straight line. so the wiffleball kind of acts like a glass bead refracting light - only it's more of a spatial lacuna connecting two parts of space that normally aren't connected -- the ion's orbits "warps" through the secant to the other side of the sphere. -- thus causing e.g. an otherwise elliptical orbit to be a "star" orbit.
Last edited by happyjack27 on Tue May 28, 2013 6:03 pm, edited 1 time in total.

ladajo
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Re: We need a new film on YouTube explaining the Polywell.

Post by ladajo »

All this certainly begs the question of the concept of "Focusing" the "lens".
The core area is cerainyly going to be messy no matter what. Another point ot consider, is that (for whatever mechanism) any ions, de-ionize and recombine with (e-), then they are now neutrals and should just continue out as waste gas. Except of course those that get hit by an ion or opposite direction gas molecule. There is no reason afterall that a recombining ion will lose direction nor final charged velocity to any real extent. We tend to think about ions for fusion given that is what we can 'drive". But the neutrals are targets too while they are 'in the zone'.
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ladajo
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Re: We need a new film on YouTube explaining the Polywell.

Post by ladajo »

It also makes me wonder about a newly created neutral getting stripped to be an ion again.
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happyjack27
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Re: We need a new film on YouTube explaining the Polywell.

Post by happyjack27 »

ladajo wrote:All this certainly begs the question of the concept of "Focusing" the "lens".
The core area is cerainyly going to be messy no matter what. Another point ot consider, is that (for whatever mechanism) any ions, de-ionize and recombine with (e-), then they are now neutrals and should just continue out as waste gas. Except of course those that get hit by an ion or opposite direction gas molecule. There is no reason afterall that a recombining ion will lose direction nor final charged velocity to any real extent. We tend to think about ions for fusion given that is what we can 'drive". But the neutrals are targets too while they are 'in the zone'.
agreed. it's a double-plus, imo, because if they de-ionize inside the WB, presumably they were low-energy ions, which is bad. but now they're neutral, so their energy is undefined; that is, while they're neutral, they can "sneak past" the electrostatic barriers into higher energy orbits, and then get ionized and say "hey, i was always here." so it's sort of connecting two spaces by way of a "neutral" wormhole. only the wormhole only goes one way - in to out.

ladajo
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Re: We need a new film on YouTube explaining the Polywell.

Post by ladajo »

Yup, my thought as well. If they can be stripped on the way in, they can be stripped on the way out.
Now how would one charactierize the "neutrals fusion" factor???
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
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happyjack27
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Re: We need a new film on YouTube explaining the Polywell.

Post by happyjack27 »

i'm not a physicists, but my first impulse would be to try to get a handle on the density of (cold) "neutrals" and a separate density of (hot) "ions".
preferably it'd have some kind of multi-dimensional plot - KE, radius, density.. something like that, that i could write a computer program to integrate over. now i'm computing fusion probability from something like density squared times barns - the KE is what determines the barns.

(but there are multiple different ways to calculate barns - basically depending on angle of incidence. for instance probably one for head on collisions, one for thermal mixes, etc. i might choose different ones or do interpolations between different ones depending on e.g. their radius. etc. in any case i'd understand that the results would be different by a few factors depending on these, and i could always go back in the code and try out different combinations.)

so what i'd do for fusion calculations is make sure that i recognize that it's an "OR" scenario. that is, not addition, not multiplication, but addition minus multiplication. and if you have multiple orders it gets even more complicated. (e.g. a or b or c, becomes a'+c-a'*c where a'=(a+b-a*b)), so i'd just cut all that complication short by using the fact that NOT (A and B) = (not A) or (not B) and vice versa. Namely, i'd calculate the probability of _NOT_ fusing in ANY of the potential combination, and then just subtract that from 1 to get the fusion probability. then that whole complicated mess becomes simply 1-(1-a)*(1-b)*(1-c)*(1-d)... etc. and it's much easier to count and make sure you counted right.

EDIT: still one'd need to be careful that they counted everything exactly once; never twice and never zero times. e.g. if all a are b, don't count a + b, just count b. i'd write out all possible combinations, mathematically speaking, and then find all intersections and unions and what not, etc., and plan out the simplest way to count that doesn't double-count any intersections or miss any. as in literally make a list and/or draw a venn diagram. and then make sure my total exactly equals the number of ions squared.

or if i was writting a program, i might take the easy way out and just have it do all NxN pairs individually. what's a quadrillion calculations... five seconds? 5 seconds for a suredly correct answer is much better than hours for one that you might have goofed on, eh? is that not _precisely_ the economic gain of computers?
Last edited by happyjack27 on Tue May 28, 2013 9:27 pm, edited 1 time in total.

ladajo
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Re: We need a new film on YouTube explaining the Polywell.

Post by ladajo »

That raises an interesting point about running the machine well hot to collect improved Q on Angle of Incidence as well as neutrals that have bled down. I have to wonder how much thought has gone into that. But of course, we can only guess in public what the actual sims look like for EMC2. They may well have a decent handle on that already for predictions.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

happyjack27
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Re: We need a new film on YouTube explaining the Polywell.

Post by happyjack27 »

KitemanSA wrote:
happyjack27 wrote:
KitemanSA wrote:But the issue is, in the center where things are densest, when the ion is Vmax and the electron is Vmin, how fast are they moving?
electrons in the center, if practice resembles theory and simulation, are quite cold. forming a hollow spikey-ball. a little faster at the cusps, where they spin.

inside the spikey-ball, they are naught. the spikey ball is hollow.
I disagree with your model. While in operation the electrons fill a rough sphere that includes most of the volume of the MaGrid. The electrons travel with significant radial motion frequently passing near the center. Wiffle Ball old boy!
Ya, I was deliberately over simplifying (and also fishing for counterpoint!). I meant to suggest that the electrostatic effects of the electrons on the ions are pretty close to net nuetral outside of that. Though again this was just to draw atrention to a specific phenomenon.

In this case we were considering bremstr- whatever losses, given that electron speed in the vicinity on the fusion effects the energy loss ratio. So the question is how significant are the hot electrons near/in the cite, in relative quantity, speed, etc, as concerns bremst-darn German names.

KitemanSA
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Re: We need a new film on YouTube explaining the Polywell.

Post by KitemanSA »

happyjack27 wrote: and faster ones leave. and new gas is puffed in, introducing ions w/a mix of energy levels.
Nope, they are introduced at the edge of the well and ionized there. Then they fall into, and gain the unique energy level of, the well. Mono-energetic.

KitemanSA
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Re: We need a new film on YouTube explaining the Polywell.

Post by KitemanSA »

happyjack27 wrote:also, come to think of it, once an ion is inside the wiffleball, it experiences no electrostatic force from the electrons (well, if you think of it discretely, as a hollow sphere, it's really not), ...
Its REALLY not.

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