Has Wiffleball Been Created Ever?

[Joseph Chikva]

As for many instabilities/ pinch effects. The convex towards the center B fields are stable . From two texts, the easiest explanation, is that concave B fields towards the walls ( the opposite perspective used in the Polywell) are stable, and can be explained simply by a potential well picture. Any charged particle that climbs (through a collision or other energy transfer mechanism) up the wall of a concave B fleld line (remember this is relative to the wall) climes a potential well . Thus it tends to fall back to the bottom of the well- to a more stable state. In a convex B field line relative to the wall, the same collision would be dropping down a potential well (gaining energy). The particle easily progresses further, and instabilities become progressively faster/ easier. Thus things like pinches are inevitable. This is fundamentally different in the Polywell configuration where the fields are convex towards the center/ concave twords the edge. This was a problem with the solenoid type mirror machines. There was concave fields (towards the center) between the magnets, and various efforts to control this failed. A Polywell, like the biconic cusp mirror machines avoid this. But the equatorial cusp losses were excessive , until modified by the Polywell geometry.

One more about mirror machines instability:

There are so many things to remember Dick for in the world of mirror fusion, not the least being his recent invention of kinetic stabilization of circular mirror machines otherwise subject to MHD instability, and its application to the Kinetically Stabilized Tandem Mirror (KSTM) [1]. I have looked at Dick’s KSTM idea myself, and find it really makes all the difference in the outlook for tandem mirror reactors, as compared with our original concept using the Yin Yang version of minimum-B mirror coils as ‘‘end plugs.’’ Poetic justice, since it was Dick who co-invented the Yin Yang in the first place. Dick also invented Direct Conversion, to make electricity by fusion without steam.

For your reference "minimum-B mirror coils" mean the same that "coils creating convex fields". And where are now Yin Yang machines? The answer is "forgotten long time ago".
http://iopscience.iop.org/0029-5515/9/3/009

Yin-yang minimum- |B| magnetic-field coil
A new conductor shape which we call a "Yin-Yang" coil is described. This coil produces a quadrupole magnetic well field, similar to the field of a Baseball-Seam coil, but with several important advantages. The Yin-Yang coil can produce a field of high mirror ratio (6, for example) with much less power than an equivalent Baseball-Seam coil. The Yin-Yang coil employs simple conductor shapes and has the flexibility inherent in two separate conductors. This permits the mirror ratio to be varied by changing the distance between the two conductors and to trap a plasma by energizing the coil segments sequentially.

And one more reference:
http://www.osti.gov/energycitations/pro ... id=4755520
Publication Date: 1969 Jan 01
Do you want to search for references about instabilities occurring in that configurations: "Baseball-Seam coil"?

So, resuming: "minimum B" or "convex field" idea was very popular in 60s-70s. The idea is very logical but real life showed us that we should not be so optimistical. "No instabilities because of convex field" is wrong statement. beta=1 is possible because we have no instabilities is wrong statement too.
Best regards

[Robthebob]

You finally explained what you mean by heating problem, thank you, only took like 3 threads. I do not know much about this technical heating problem, I'll go ask a professor, and dont worry, he's a tok guy.

Have you seen this?
http://hardware.slashdot.org/story/12/0 ... -questions

I went through most of it, and most of it talked about control issues; this coming from a group of tok guys, but rest assure I'll go find someone that can answer my questions.

Lastly, hopefully, first of all, we were comparing toks and stellarators, when I said temperature is not a problem, it means toks do not have that huge of an edge (if it has an edge at all) over stellarators in terms of heating the plasma. I explained why.

[Joseph Chikva]

Have you seen this?
http://hardware.slashdot.org/story/12/0 ... -questions

No, I have not but will read when find a time. Thanks.

By the way, have you seen this?
http://www.sunist.org/shared%20document ... r%2011.pdf
Does the "spherical cusp" shown in Fig. 11A4 not similar to Polywell's field?

[Skipjack]

Man, arent you a meanie. I want you to remember this is the day that you made the polywell forums into a place to throw meaningless insults at other posters instead of discussing scientific matters like adults.

Dude, dont ever go into the General forum then. Its been like that there forever now

[kcdodd]

I think it should be mentioned that these min-b plugged mirror machines did not die out because they failed, but because of funding cuts. The people promoting them projected Q=1 as it was, and were arguing for a fusion fission hybrid concept even back in the 70s (and before though I don't have the dates handy). However, when Tokamak's were promising Q>20, well you see the problem. The Mirror Fusion Test Facility (MFTF) was canceled right after it was completed in 1986 for some $300M (four years *after* TFTR was completed in 1982), never even turning it on. It utilized superconducting magnets, and to my knowledge would have been the first test of their use with a fusion burn.

Now tokamaks struggle to get past Q=1, with the fusion-fission hybrid workaround being worked on until they can get past Q=10. The problem with min-b and mirror machines were not so much that they under-delivered, but that they under-promised. To use the fact that work on them stopped as some sort of evidence to their capability is very deceiving and fallacious.

[Skipjack]

Fully agree with you Carter!

[Joseph Chikva]

To use the fact that work on them stopped as some sort of evidence to their capability is very deceiving and fallacious.

But do we not have the right to use the fact as evidence that convex field machines is not novelty and they also suffer instabilities? Despite to distributing here exclamations: "Dude, convex field! Steady state – no instabilities!"
As presence of instabilities means that beta=1 is impossible for any magnetic confinement machines.
And particle losses in Polywell is not experimental evidence of beta=1
I did not want and did not say nothing more.

Why this type of machines are forgotten is also the subject of discussion. But the fact is only one: nobody from qualified plasma physicists exept very few people considers mirror machines even theoretically.

By the way, unlike TOKAMAKs Stellarators also are "minimum B machines". Nevertheless, no advantages and much complex. So, even more expensive.

So, logically on base of 60 years fusion research history we can come to conclusion that " minimum B principle" as such is less important (useful). And some other ways for slowing down instabilities development should be found. And for TOKAMAKs this way is to run at comparativelly low (lower than 0.4 but ~0.1 in reality)beta.
For other approaches situation is not so clear.

[Robthebob]

"Dude, convex field! Steady state – no instabilities!"

No one said this, first polywell is a pulsed machine, I dont know if we have plans to make it steady state. Second, we never said no instabilities, we said way more stable, because polywell, if I'm wrong someone please correct me, is bottom of head stable, not top of the hill stable.

About mirror machines in the past, I dont think anyone on this forum possess enough technical understanding to say anything about those machines. One thing I will say is 11A4's toroidal multipole cusp picture isnt the same configuration as WB6 or 7, I personally do not know the design specifics of how to build a polywell, (like how many poles and where to place them). What are the differences from one configuration to another?

Lastly, of the limited amount of education on mirror machines, the idea of electron re-circulation has never been talked about until polywell. Did they not do that in the past?

We do claim that polywell is not a thermalized machine.

A question for the other posters, refer to my earlier posts for the first set of questions, also I'm curious about how the fuel is confined in the polywell; isnt it mainly electrostaticly? As in the fuel will not get confined in the wiffleball when it forms, nor does it get to re-circulate along the b field lines like the electrons.

[Joseph Chikva]

"Dude, convex field! Steady state – no instabilities!"

No one said this, first polywell is a pulsed machine, I dont know if we have plans to make it steady state. Second, we never said no instabilities, we said way more stable, because polywell, if I'm wrong someone please correct me, is bottom of head stable, not top of the hill stable.

As it appear to us, emc2 arent focusing mainly on various power balance, profile balance, etc etc to make sure polywell doesnt blow up in their face; while for donut machines, often times, it is this sort of power balance, profile balance, etc or else instabilities happen.

At this point though, the community's expertise completely runs out, I dont know if anyone who's able to say anything publicly has the knowledge to talk about control in polywell. This just hasnt been a problem talked about in past publications.

About mirror machines in the past, I do not, I dont think anyone on this forum, possess enough technical understanding to say anything about those machines. One thing I will say is 11A4's toroidal multipole cusp picture isnt the same configuration as WB6 or 7, I personally do not know the design specifics of how to build a polywell, (like how many poles and where to place them). What are the differences from one configuration to another?

Lastly, of the limited amount of education on mirror machines, the idea of electron re-circulation has never been talked about until polywell. This could be that those machines were attempting to confine a maxwellian plasma, pitch angle-esque losses (I dont know what type of term to use) cannot be avoid due to plasma interactions. On the other hand, imagine if you can stop the plasma from interacting and put the species all away from the pitch angle; what would happen then?

We do claim that polywell is not a thermalized machine.

A question for the other posters, refer to my earlier posts for the first set of questions, also I'm curious about how the fuel is confined in the polywell; isnt it mainly electrostaticly? As in the fuel will not get confined in the wiffleball when it forms, nor does it get to re-circulate along the b field lines like the electrons.

"Steady state" in English means infiniteness operation? I thought that it means "no instabilities". And "no instabilities" was said many times. And namely the presence of instabilities means the lack of possibility to run at beta=1. Recall swimming pool analogy.
"Spherical cusp" pic in 11A4 Fig. is identical to Polywell's field and not and not "toroidal multipole cusp" regardless to what that field is intended to confine - thermal plasma or only electrons.
Best regards

[KitemanSA]

"Dude, convex field! Steady state – no instabilities!"

No one said this, first polywell is a pulsed machine, I dont know if we have plans to make it steady state.

Heck yes, the intent is to make it steady state. But if it can't work that way, a number of folks think a rapid pulsed machine may be a way to go also.

Second, we never said no instabilities, we said way more stable, because polywell, if I'm wrong someone please correct me, is bottom of head stable, not top of the hill stable.

Polywell (IIRC) does NOT exhibit a number of the worst case instabilities that plague the toks. Since they have only been run in small scale, there may be instabilities that are peculiar to Polywells but haven't been found yet. Tick tock.

...
We do claim that polywell is not a thermalized machine.

My understanding is that Polywell will not work if it thermalizes. I would love to be wrong on that!

A question for the other posters, refer to my earlier posts for the first set of questions, also I'm curious about how the fuel is confined in the polywell; isnt it mainly electrostaticly?

Yes (or as some folks say electro-dynamically since the electrons are moving and generating an opposing B-field inside the core).

As in the fuel will not get confined in the wiffleball when it forms, nor does it get to re-circulate along the b field lines like the electrons.

The ions WILL will be confined inside the wiffleball since the WB confines the electrons which form the electro-potential well which confines the ions. The ions won't be primarily confined DIRECTLY by the wiffleball since most won't climb high enough up the well to do so.
You are correct about the "doesn't recirculate" part though. Indeed, ions that do escape gain additional energy from the MaGrid charge as they streak to the chamber wall.

[93143]

And "no instabilities" was said many times.

Yeah, by you. It's a straw man you dreamed up on your own.

The closest anyone else ever came was Robthebob's statement that instabilities unique to tokamaks do not occur in stellarators (a tautology really, but it's evident what he meant), and my statement that a Polywell's magnetic configuration is MHD-stable. Neither of these imply "no instabilities" - Robthebob immediately distanced himself from the implication, in fact.

And namely the presence of instabilities means the lack of possibility to run at beta=1. Recall swimming pool analogy.

There's a problem with either definition or understanding here. Maybe both.

As I understand it, exceeding beta=1 in a tokamak (assuming you could get there in the first place, which I'm well aware you can't) would result in a complete blowout of the plasma, since it is unstable to ballooning mode.

Polywell is MHD stable, so ballooning mode isn't a problem. What happens is that at beta=1 the cusps are at minimum size, so if you exceed that, they start growing and leaking more - a negative-feedback mechanism.

Therefore, if I've understood this correctly, it should be possible to run a Polywell at an average beta of 1, via appropriate control of fuel and electron supplies. This would render your objection, while technically correct, nitpicking in the extreme.

You may have noticed that since pushing on the magnetic field in a Polywell strengthens it, the definition of beta>1 depends wholly on the cusp behaviour...

[Joseph Chikva]

Polywell is MHD stable, so ballooning mode isn't a problem. What happens is that at beta=1 the cusps are at minimum size, so if you exceed that, they start growing and leaking more - a negative-feedback mechanism.

First of all you can not provide evidence of MHD stability of Polywell. While I can provide references about numerous instabilities in convex field machines. Leakage through the cusps will be observed at beta<1 too. 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?

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?
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? Please provide at least one reference of experimental evidence. As by my information these reasoning were popular in 60-70s but have not been proved then.

[93143]

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.

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.

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.

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. The terminology has been used that way here in the past.

The magnetic configuration has very little to do with two-stream, for instance. On the other hand, a Polywell should not exhibit ballooning-mode instabilities.

[kcdodd]

To use the fact that work on them stopped as some sort of evidence to their capability is very deceiving and fallacious.

But do we not have the right to use the fact as evidence that convex field machines is not novelty and they also suffer instabilities? Despite to distributing here exclamations: "Dude, convex field! Steady state – no instabilities!"
As presence of instabilities means that beta=1 is impossible for any magnetic confinement machines.
And particle losses in Polywell is not experimental evidence of beta=1
I did not want and did not say nothing more.

Why this type of machines are forgotten is also the subject of discussion. But the fact is only one: nobody from qualified plasma physicists exept very few people considers mirror machines even theoretically.

By the way, unlike TOKAMAKs Stellarators also are "minimum B machines". Nevertheless, no advantages and much complex. So, even more expensive.

So, logically on base of 60 years fusion research history we can come to conclusion that " minimum B principle" as such is less important (useful). And some other ways for slowing down instabilities development should be found. And for TOKAMAKs this way is to run at comparativelly low (lower than 0.4 but ~0.1 in reality)beta.
For other approaches situation is not so clear.

I don't see how that follows at all. If it was TFTR that was cancelled and not MFTF, then you would now be arguing that tokamaks are not a novelty and should stay forgotten, and are less useful. You seem to think that funding priorities have this magic power of foretelling the outcome of experiments before they're even conducted.

[Robthebob]

As in the fuel will not get confined in the wiffleball when it forms, nor does it get to re-circulate along the b field lines like the electrons.

The ions WILL will be confined inside the wiffleball since the WB confines the electrons which form the electro-potential well which confines the ions. The ions won't be primarily confined DIRECTLY by the wiffleball since most won't climb high enough up the well to do so.
You are correct about the "doesn't recirculate" part though. Indeed, ions that do escape gain additional energy from the MaGrid charge as they streak to the chamber wall.

Okay, I think this is what my professors meant when he said when you talk you gotta be careful. What I mean to ask is this:

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?

Steady state does mean indefinite operation, but it does not mean no instabilities. Again, run time and quality of control are not always related; they may not even be related in general.

In hindsight again, I realized we have definition difference with the word "instability". In some context it means ones leading to disruptions, in some context it means ones leading to swifting of modes (usually from a more desired mode to a less desired mode), sometimes it means losses, etc. Let's call instabilities, and this will sound dumb, something that needs controlling.

There are instabilities in polywell in the form of electron losses. Your statement that instabilities equates beta=/=1 is non sequitur. It has to do with rates of loss and growth of rates of loss.

1. If the rate of loss at the start doesnt equate to the rate of input, like you throw 10 apples in and none of the 10 apples stay, but the growth rate will lead to the loss rate=100% at some point before beta=1, then beta=/=1
2. If all the same as 1, but growth rate will not lead to loss rate=100% before beta=1, then beta can get to 1
3. If all the same as 1, but the growth rate is zero or negative; the more apples you throw in, the better the rate, then beta can get to 1.

If I understand the description of polywell correctly, polywell actually falls under 3, because the closer you get to beta=1, the smaller the cusps in the core of the machine.

Even the paper you linked talked about this ballooning mode, (they call it an instability, it may not be an instability to us), now whether this ballooning process does reconfigure the field structure in the core of the machine to reduce the size of the cusps, I dont know.

Did people discover wiffleball effect without knowing they did so all those years ago?

All those things you said that we said is at worst you trying to straw man us or at best bad communication and misunderstanding.

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

This is what I think happens:
you shoot more and more electrons into the machine, you're somehow able to build and sustain a denser electron cloud the more electrons you shoot in, but as the electron cloud grows in density, the electrons also wants to spread out; when the electrons tries to spread out, it balloons into the field of the machine, which reconfigure the field structure of the machine and makes the cusp smaller. This event "relocates" most electrons getting shot into the system into the core (easy to get in, hard to get out). The more electrons in the core, the more it tries to spread out, and the more it pushes on the field of the machine and the smaller the cusp. And you just keep going until you get to beta=1.