Has Wiffleball Been Created Ever?

[93143]

when you talk you gotta be careful.

Good advice.

When wiffleball effect takes place, the cusps grow smaller, so the electrons will get stuck in the core of the machine instead of having to re-circulate out and in the machine. My question is, does the ion also get stuck in the core of the machine like the electrons?

Yes, but the effect is different. The ions, ideally, are low-energy at the wiffleball edge, so the confinement is primarily electrostatic. If a particular ion were at high energy at the edge, it would see the wiffleball effect just like the electrons, but since its gyroradius is larger the confinement would not be as good.

Steady state does mean indefinite operation, but it does not mean no instabilities.

In this context, that is correct. If you want to get technical, "steady state" usually implies no time rate of change of relevant quantities, but that's not what is meant here.

To 93143, I dont know if you know, but doesnt polywell undergo something similar to a ballooning process in the core of the machine?

Yes; that's what forms the wiffleball - you jack up the plasma pressure until it inflates the magnetic field and squeezes the cusps almost shut. But due to the magnetic configuration this "ballooning" effect isn't unstable like it is in a toroidal machine. That's the difference.

[KitemanSA]

Leakage through the cusps will be observed at beta<1 too.

Of course. With Polywell, beta=1 means the point at which cusp losses are at a minimum, due to the wiffleball effect.

I was under the impression that beta=1 is the point where the electron pressure (with whatever miinor ion enhancement there may be) is equal to the maximum the B-field can be compressed. Any further and the B-field in essense passes thru flat to concave and sufferes the same kind of blow-out as a tok might at beta=~.4, but perhaps for different reasons.

And yes, I am using the shorthand that beta=1 is really saying that beta is slightly less than "one" exactly so that minor perturbations do not progress to blow-out. This is what I believe that almost everyone on this site means by beta = 1 except those who are looking for ways that prove that others are wrong.

[KitemanSA]

[/quote]

When wiffleball effect takes place, the cusps grow smaller, so the electrons will get stuck in the core of the machine instead of having to re-circulate out and in the machine. My question is, does the ion also get stuck in the core of the machine like the electrons?

To a degree, yes. Dr N pointed out the even charged fusion products would get stuck for a small number of passes in a production level machine and they have lots of energy. A lower energy fuel ion (at least one that has been upscattered enough to reach the B-field, will also be trapped for a number of cycles until it finds a cusp and escapes.

[KitemanSA]

To 93143, I dont know if you know, but doesnt polywell undergo something similar to a ballooning process in the core of the machine?

Yes; that's what forms the wiffleball - you jack up the plasma pressure until it inflates the magnetic field and squeezes the cusps almost shut. But due to the magnetic configuration this "ballooning" effect isn't unstable like it is in a toroidal machine. That's the difference.

With toks, where the plasma is basically INSIDE the B-field running along the B-field lines, a "ballooning" mode would expand the plasma (and the B-field) weakening the field leading to blow-out. In the Polywell, where the plasma is effectively OUTSIDE the B-field trying to CROSS the B-field to the MaGrids, a ballooning of the plasma compresses the B-field making it stronger... TO A POINT. Eventually, the pressure will invert the field and the same type of blow-out will happen. As I understand it, this point is called beta=1.

[93143]

No, I think you're wrong. It's the cusps that "blow out"; that is, they begin to widen under plasma pressure.

The field generated by the magnets will continue to get stronger when pushed on as long as the plasma is inside the magrid. The plasma will never "blow out" at any point that wasn't already a cusp.

I don't think it matters whether the field is convex or concave under plasma pressure, as long as it is convex initially.

...

If someone can explain why this is wrong, I will have learned something.

[kcdodd]

As I said in my much earlier post, I don't think a "wiffle ball" can form in equilibrium in the way that is normally portrayed. That is, literally a plasma ball. The magnetic pressure and plasma pressure could not be in equilibrium everywhere. At least not with the coil design as it is. That comes from seeing the results of the solvers Indrek and I made. I am not sure if one could come up with a coils where it would be in equilibrium though.

[Joseph Chikva]

Leakage through the cusps will be observed at beta<1 too.

Of course. With Polywell, beta=1 means the point at which cusp losses are at a minimum, due to the wiffleball effect.

May be. But please provide corresponding reference. Better if that would be the experimental evidence.

And please show your negative-feedback mechanism for other machines with convex fields. Or do you mean that such a mechanism is only Polywell's feature?

No, it should at least sort of work for any purely convex-field machine. But if the machine cannot operate in wiffleball mode or something like it, cusp losses near beta=1 will be high, and the loss slope should be low, making the feedback weak.

The "negative feedback" I'm referring to is only for beta>1. For beta<1, it's positive feedback, and you need to watch out for that when feeding fuel and electrons.

I am mechanical engineer by my first education. So:
Let’s consider the pressure vessel with several small enough holes allowing some quantity of being there gas to leak and also with several holes for injection of higher pressure gas inside. Let’s inside flow exceeds gas leakage. So, pressure in vessel should be constantly increased. Let’s call beta=1 when gas pressure inside vessel is equal to strength limit of vessel. What will happen with vessel if pressure will reach that limit? Can leakage hole preserve vessel from explosion?
And what is beta>1 Not a case when pressure inside exceeds the strength limit. What feedback you talk about?

And why are you so sure that nobody said me "no instabilities"? TOKAK has, Stellarator has not. Then all toroidal have, cusp machines have not. Nobody told?

Nope. Unless I missed something, no one ever claimed that.

What was claimed is that there are classes of large-scale first-order instabilities that toroids have and cusp machines don't, and instabilities that tokamaks have but stellarators don't.

Not all fusion machines can be expected to exhibit comparable plasma behaviour. For instance, Polywell is immune to ballooning mode. Claiming that any differences are due to different levels of development and understanding is not supportable given the evidence. It remains distinctly possible that Polywell is simply a much better idea than tokamak.

Yes, you missed that many people are saying “no instabilities at all”. And yes, not all fusion machines exhibit comparable plasma behavior. But all fusion machines suffer from instabilities. Not sure about ballooning mode, but surely not kink or sausage instabilities, but surely has 2-stream or Wiebel. And nobody investigated how those instabilities will make influence on possible beta. But all here say: beta=1, scaling law B^4 R^3. Wrong: right scaling law is beta^2 B^4 R^3 where beta is decreasing function of B. And in some cases when instabilities would have destructive scale beta can become equal zero.

And what is "MHD stable"? Not an absence of at least macro-instabilities? May be we really use different definitions.
And why "MHD stable"? Because pushing force lines we make those stronger?

Yeah, that's all I meant. That the geometry makes it immune to certain classes of macroinstability.

Please provide examples from fusion history. As I also heard these reasonings about advantages of convex fields (minimum beta machines) but we have clear examples that minimum B stellarators have not any advantage vs. TOKAMAK and also suffers macro-instabilities.

The magnetic configuration has very little to do with two-stream, for instance

Right.
I know three stabilizing factors slowing down 2-stream:
-velocity spread in streams (electron beam and background plasma in Polywell case)
-high relativism of at least one stream
-strong solenoidal field expands stability area
Now please explain which one from mentioned three is possible in Polywell for slowing down electron-ion 2-stream instability.

On the other hand, a Polywell should not exhibit ballooning-mode instabilities.

Wrong. See example of pressure vessel in this post.

[Robthebob]

If a particular ion were at high energy at the edge, it would see the wiffleball effect just like the electrons

I do not understand this. I'm under the impression that the WB effect is just the result of the ballooning effect of electrons at the core of the machine, since the ballooning effect changes the field structure to allow particles to come in easy but leave harder, electrons will effectively relocate themselves to the core.

If you inject fuel into the system when the WB effect is already in place, I can see the ions might go into the core and have a harder time leaving, but I dont see how this have to do with high energy ions at the edge, or something... I'm missing something here.

[Robthebob]

Man, that was a long post Joe, I dont know if 93143 should bother answering it.

Regardless of what you said tho, it's pretty obvious. We know ballooning processes happen on mirror machines, we know ballooning will alter the machine's field by pushing on it, now here's the the missing link.

what are the exact effects pushing on the machine's field in polywell, in the core?

We claim that the the ballooning process alters the field in the core in such a way that it's more difficult for electrons to escape the core than before.

If this claim is true, it's pretty evident that the WB effect occurs.

[Joseph Chikva]

Man, that was a long post Joe, I dont know if 93143 should bother answering it.

Regardless of what you said tho, it's pretty obvious. We know ballooning processes happen on mirror machines, we know ballooning will alter the machine's field by pushing on it, now here's the the missing link.

what are the exact effects pushing on the machine's field in polywell, in the core?

We claim that the the ballooning process alters the field in the core in such a way that it's more difficult for electrons to escape the core than before.

If this claim is true, it's pretty evident that the WB effect occurs.

If all said by me is "pretty obvious" for you, we would not argue at all. Seems to me that not so obvious as said by me you check with your professors. And I do not know what "ballooning process" is and how it alters the field in the core. Sorry.

[KitemanSA]

That comes from seeing the results of the solvers Indrek and I made. I am not sure if one could come up with a coils where it would be in equilibrium though.

The graphic that had been at your site is now not available. Can you bring it back?

[Robthebob]

http://www.sunist.org/shared%20document ... r%2011.pdf

The section under ballooning mode. The electrons have intrinsic b fields that will alter the fields of the machine. It's a little bit poetic that your source provided support for the WB effect.

Also, dont be childish, I said I will speak to my professors about donut machines, not polywell, so that has nothing to do with this current conversation.

Lastly, I didnt want to really bring this up, because it will bring more meaningless arguments. However, indeed you just compared a real life metal vessel filling up with gas with a magnetic trap filling up with electrons. It's once again non sequitur.

First, magnetic fields are not like metal containers. Their structure can be gradually changed by the fields of the electrons. Second, the analogy of machine field pressure and container structural limits is not a good one. On polywell, after the "blow out", if you reduce electron gun current, beta will go back down. After a blow out in a metal container, it wont return back to its original shape.

[Joseph Chikva]

Lastly, I didnt want to really bring this up, because it will bring more meaningless arguments. However, indeed you just compared a real life metal vessel filling up with gas with a magnetic trap filling up with electrons. It's once again non sequitur.

In the first approximation it is quite relevant. As if you talk about gas pressure and magnetic pressure, so you use mecanical analogy. And all speaking about beta use such an analogy.
And pressure vessel e.g. solid fuel rocket motor having a nozzle through which gas flows out may explode if internal pressure exceeds such limit.
http://books.google.ge/books?id=Q1yJNr9 ... ng&f=false

Rockets that explode upon firing because internal pressures exceed the casing strength

[ScottL]

Lastly, I didnt want to really bring this up, because it will bring more meaningless arguments. However, indeed you just compared a real life metal vessel filling up with gas with a magnetic trap filling up with electrons. It's once again non sequitur.

In the first approximation it is quite relevant. As if you talk about gas pressure and magnetic pressure, so you use mecanical analogy. And all speaking about beta use such an analogy.
And pressure vessel e.g. solid fuel rocket motor having a nozzle through which gas flows out may explode if internal pressure exceeds such limit.
http://books.google.ge/books?id=Q1yJNr9 ... ng&f=false

Rockets that explode upon firing because internal pressures exceed the casing strength

Joseph, he's saying in the Polywell, if you have a blow-out event, you can dial back and recover the wiffleball shape which is something you can't do with a physical vessel. The idea of the blow-out is the same, however; the recovery is not at all the same as there is none in your casing/vessel/etc...

[Robthebob]

In hindsight, I really shouldnt have said that, because I dont know if it's possible to dial it back.

It's intuitive to me that it's a gradual process. From what I've heard, the "blow out" happens because the ballooning process is literally opening the cusps back up, allowing for electrons to leave easier than before.

To me, and I have no idea if it's true, if you reverse the process, the cusps will begin to close up again, and you get back the Wiffleball.