Questions

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

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D Tibbets
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Post by D Tibbets »

ladajo wrote:
I suppose it's possible they reach an equilibrium at unacceptable losses
This is the lines of my thinking. I agree with gbrown that the patent is from pre-Ah-ha!, but in that, since ah-ha, we have not seen a good public revisit to scaling. The re-circ (or oscillating as our majority seems to think) is obviously important. But as we increase e- population and drive levels, it does beg the question. But, I remain faithful that excellent confinement means exactly what it says.
Try the 2008 patent application instead of the ~ 1988 first patent.
See bottom of next post.

Dan Tibbets
To error is human... and I'm very human.

D Tibbets
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Post by D Tibbets »

The Brillouin limit is sometime described as an absolute limit, but this is apparently not the case. Bussard addressed this (see the 2008 EMC2 patent application).
And this study exceeded this limit.

http://pop.aip.org/resource/1/phpaen/v4 ... horized=no


This might mention Brillouin limit. It does present evidence that electron thermalization may not occur in time frames of over 500 microseconds ( ~ twice the non recirculated electron lifetime in the Polywell (WB6)).

http://www.dtic.mil/dtic/tr/fulltext/u2/p012563.pdf


As far as the cusps being areas of zero magnetic strength, while this is true, it is misleading. What is important is how quickly the opposing fields build on either side of this null magnetic region (very close to infinity thin) to levels where mirror reflection occurs or adiabatic bouncing of the electrons results in a new direction where the electron is not directed deeper into the cusp geometry. I believe these are two separate mechanisms. This is illustrated in one of Bussard's early papers. In a collisionless plasma this would be much like a game of billiards where the ball bounces off of the bumpers angled towards the hole, but the ball bounces several times and is deflected away from the hole. Of course in a collisional plasma things are much more complicated.

As far as instabilities, I think a key consideration is that the Polywell is quasi spherical. This is very different from cylindrical or torus geometries. Also, instabilities may not be detrimental. I assume that POPS techniques introduces or takes advantage of potential instabilities to created advantagous conditions.

In any given cusp the field lines are in the same direction. Either inwards or outwards. This is (I think) almost totally irrelevant concerning the electron gyro motion direction. If the electron hits the field line perpendicurly, it will be deflected in a Northward direction, either in a ~1/2 gyro orbit as it adiabatically deflects or is captured on the field line. If captured, this would introduce a preferred direction for the electron, but only for it's first pass along the field line, once mirror bounced (reversed), on the field line, it's direction is in the opposite direction.. If 'cusp confinement' of electrons is ~ 60 passes (Wiffleball confinement would be even better at a few thousand passes) and this applies to these captured electrons equally to those adiabatically deflected back into the B field free central region, then the initial preferred direction along the field line would be quickly diluted to a near random directional field line average. I speculate that this would moot any concern about the initial field line direction preference. And this is before considerations of collisional interactions, and that electrons that meet and are captured onto a field line will only rarely be traveling perpendicular to the field line. Even with good central focus of the electrons- near radial motion, the B field lines are always curved away from the center, so even in a theoretical perfect radial situation there would only be very rare situation where the electron enters the B field prefectly perpendicular to the field lines. How much deviation from perpendicular entry is needed before the deflection is not in a Northward direction (if I'm keeping the charged particle direction in a magnetic field straight (N pole attracting electrons ))? In any case , I suspect that the direction of the magnetic field is ( very nearly?) irrelevant in this regard. The average electron would not show any preference for which cusp (N pole inward, or N pole outwards) they accumulate in, or escape through..

I do wonder about the free cusps verses the cusps that have an electron gun shooting new electrons through. These guns would seem to have a side effect of acting like a cusp plugging electron repellar. Is it better to have an e gun at every cusp? Is it better to have the minimum number of guns? What compromises in e gun standoff and number gives the best results? There is mention of the best e gun standoff distance in the 2008 patent application.

Parent page with lots of other pertinent papers:
http://www.askmar.com/Fusion.html

and direct link:
http://www.askmar.com/Fusion_files/Pate ... 187086.pdf

Dan Tibbets
To error is human... and I'm very human.

TallDave
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Post by TallDave »

KitemanSA wrote:Just to refresh, the report stated:
the WB-8 device has demonstrated excellent plasma confinement properties
What else would it be confining? :D
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

ladajo
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Post by ladajo »

Opinions.

KitemanSA
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Post by KitemanSA »

The discussion seemed to be regarding electrons, not plasma.

mattman
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Post by mattman »

Hello,

Would anyone like to write a post for "The Polywell Blog" The blog is getting 50 hits a day - your stuff would get read. Writing a post is a challenge. Your post needs to be:

1. Understandable - This is paramount.

2. Accurate - Science as it is, not as we would like it.

3. Backed up by references.

The posts need to be of very high quality. It takes time to write something good – and it is good to have it looked at by others. Since this is a hobby for most of us – there will be mistakes and things may not go quickly. However, opening the blog up to the larger community is the way to go. Message me on Talk-Polywell if you are interested.

Thanks guys.

TallDave
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Post by TallDave »

Sorry Kite, your emphasis makes much more sense when I actually read the comment above it. :roll:
ltgbrown wrote:When the word confinement is used concerning electrons, I think we might need to think a little differently. Electrons are not necessarily confined in the classical since. They are allowed to circulate. By "allowing" them to circulate outside the magrid, their lifetimes are increased. So, you could say their "confinement" is extended by allowing circulation. It was this supporting circulation that was Bussard's ah ha moment (specifically, forming the elements of the magrid to reduce the intersection of magnetic lines of force with any metal, thus increasing lifetime, allowing more circulation, and therefore "more confinement".) So, a 1987 patent that talks about lost by collisions with walls and structures does not include the idea of circulation.

So, my thinking is the "excellent confinement" comment is about ions and Bussard knew what he was talking about. No assuming, no being overly optimistic.
I think in this context "confined" only means the "confined" electrons do not contribute to losses. What we really want to know is "How much energy does it cost to operate?"

With recirculation, the electrons do still eventually end up at the walls or structure; the 2008 patent is the same in this respect. Recirculation only buys them more time (thus increasing confinement).

Restricting their remarks to ions would be somewhat deceptive as the losses are supposed to be dominated by electrons. As Kite says, they are most likely talking about both (i.e. "plasma").
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

D Tibbets
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Post by D Tibbets »

I vote for electron containment. The fuel ion magnetic containment is mostly meaningless as they are predominantly contained by the electron induced potential well- electrostatic containment. Losses are dominated by electron losses, so they are the primary concern both to input energy costs, and, because ion concentrations will be almost the same as magnetic electron containment, the ion density/electron density achievable. This second consideration is critical for useful fusion rates.

Of course, since the electrons in the plasma only exceed the ions by ~ 1 ppm, using plasma as the descriptive term is convenient , but it is not representative of the difficulty of achieving those conditions as it does not indicate the costs/ needed efforts needed for specific electron containment with or without recirculation. Ions are mostly along for the ride.
When considering the triple product- time, temperature, and density. All is dependent on the maintainable electron population within the magrid, and the efforts needed to achieve this- magnetic confinement of electrons to maintain a certain density, and recirculation efficiencies that reduce the energy input costs needed to replace escaped electrons. There is no mechanism to recover escaped ions, they actually cost energy as they are accelerated away from the magrid. But, this is apparently a relatively infrequent occurrence compared to the electron dynamics. The electrons dominate the energy loss mechanisms, so they are the species that has to be controlled for 'excellent confinement'.

Dan Tibbets
To error is human... and I'm very human.

KitemanSA
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Post by KitemanSA »

Excellent! Let's vote about what they meant rather than just read what they said. :roll:

ladajo
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Post by ladajo »

:)

happyjack27
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Re: Questions

Post by happyjack27 »

as far as cusps go - and this relates to questions 1,2, and 3. there is no such thing as a plane cusp. cusps lie on a surface and a surface is already a plane so the only things that can exist on it must have dimension no more than 2 and if there was a 2-d patch with net zero magnetic field on a surface, then that surface would not be a surface that is bounded by magnetic fields and cusps. one would have to continue the edges of the surface through that patch to make it such.

a cusp is not the absence of a magnetic field. a cusp is a boundary between magnetic fields. in a sense, yes, as you asymptotically approach the boundary, the net magnetic field strength from the fields asymptotically gets weaker. but that is precisely what a cusp is. the space right between me and my computer screen has -- for most practical purposes -- negligible magnetic field. it is not a cusp.

ladajo
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Post by ladajo »

Concur. I think at best you could "try" to argue a tangential cusp plane, but even that does not work.

KitemanSA
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Re: Questions

Post by KitemanSA »

happyjack27 wrote:a cusp is not the absence of a magnetic field. a cusp is a boundary between magnetic fields. in a sense, yes, as you asymptotically approach the boundary, the net magnetic field strength from the fields asymptotically gets weaker.
This is not quite correct.
What holds the electron in is the tanjential part of the field. As you get closer to a cusp, the total field usually gets stronger (except in a funny cusp). But as it gets stronger it also turns radial. Thus the TANGENTIAL part approaches zero. And since it is the tangential part that hold the electron in...

happyjack27
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Re: Questions

Post by happyjack27 »

KitemanSA wrote:
happyjack27 wrote:a cusp is not the absence of a magnetic field. a cusp is a boundary between magnetic fields. in a sense, yes, as you asymptotically approach the boundary, the net magnetic field strength from the fields asymptotically gets weaker.
This is not quite correct.
What holds the electron in is the tanjential part of the field. As you get closer to a cusp, the total field usually gets stronger (except in a funny cusp). But as it gets stronger it also turns radial. Thus the TANGENTIAL part approaches zero. And since it is the tangential part that hold the electron in...
ah yes. i knew i wasn't exactly explaining it right. the image formed in my mind from my explanation just didn't fit. thanks for the correction.

also i should add that cusps by definition (i believe) lie on the boundary of a volume. and the boundary of a volume is a surface thus they lie on a surface.

KitemanSA
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Re: Questions

Post by KitemanSA »

happyjack27 wrote:also i should add that cusps by definition (i believe) lie on the boundary of a volume. and the boundary of a volume is a surface thus they lie on a surface.
I am not sure about this, but it seems quite possible that the definition of "cusp" changes with the basic subject, so a mathematical cusp may be different than a magnetic cusp, may be different than a gravitational cusp.
Last edited by KitemanSA on Tue Oct 18, 2011 12:28 pm, edited 1 time in total.

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