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[KitemanSA]

You started talking about beams but you seem to hav e gone off into never-never land.

This time I started talking about potential well definition. And showed where you was wrong. As the depth of potentiall well is function of density distribution and so, location does matter.
That is all.

I suspect L's description is a bit simplistic. All you have to do it introduce electrons "with a radial energy ~equal to the desired potential well depth" inside the MaGrid. However, he is still correct that no "beam" behavior is needed.

it does not matter how electrons are distributed in reactor once the enter inside it.

I don't see how those statements are equal at all. So how can I be wrong for not writing something I didn't write?

But just as a set ot thoughts, does a Polywell NEED to have two beams of plasma opposing each other? No.

How bout 4 beams? Nope, not that either.

Is absolutely uniform distribution about the sphere needed. Nope,

How bout an icosadodecahedral pattern. Nope, doesn't need that either.

I fail to see how the Polywell NEEDs ANY specific distribution except that the distribution should include as great a percentage of radial energy as practical. I also suspect that it will approximate sphericity as well as the MaGrid shape will allow. But "beam" behavior? Nope.

[Joseph Chikva]

You started talking about beams but you seem to hav e gone off into never-never land.

This time I started talking about potential well definition. And showed where you was wrong. As the depth of potentiall well is function of density distribution and so, location does matter.
That is all.

I suspect L's description is a bit simplistic. All you have to do it introduce electrons "with a radial energy ~equal to the desired potential well depth" inside the MaGrid. However, he is still correct that no "beam" behavior is needed.

it does not matter how electrons are distributed in reactor once the enter inside it.

I don't see how those statements are equal at all.

That is your problem. And not mine.
I've just recall that once Dan has link of article in which achievable potential of virtual cathode is estimated as 0.14 from applied voltage.
As I understand this corresponds to beta=0.14 (questionable as may be proportional to square).
For your reference virtual cathode is created with the help of beams and with nothing else. No beams – no virtual cathode and consequently no potential well.
Good luck.

[ladajo]

Joseph, Polywell is not a beam machine. It can be reduced for simple analysis to be viewed as a type of beam interaction, but the machine as a whole is not a beam machine, think of it as a soup. The soup interactions are based on (yes, density) the number of e, but also the velocity (ever changing) and directions they are travelling (ambigous cloud, cycling through center).

[Joseph Chikva]

Joseph, Polywell is not a beam machine. It can be reduced for simple analysis to be viewed as a type of beam interaction, but the machine as a whole is not a beam machine, think of it as a soup. The soup interactions are based on (yes, density) the number of e, but also the velocity (ever changing) and directions they are travelling (ambigous cloud, cycling through center).

Thanks, I know what Polywell is: Unlike fusor in which ions are attracting by negatively charged grid, Polywell is the machine attracting ions with the help of virtual cathode located in the center (so, location of electrons does matter).
Virtual cathode is responsible on creation of potential well.
Virtual cathode is created with the help of beams. And denser virtual cathode creates deeper potential well.
You need the right distribution (by location) of electrons density in Polywell. This distribution can be described by number density or potential gradient.

[KitemanSA]

Thanks, I know what Polywell is: Unlike fusor in which ions are attracting by negatively charged grid, Polywell is the machine attracting ions with the help of virtual cathode located in the center (so, location of electrons does matter).
Virtual cathode is responsible on creation of potential well.
Virtual cathode is created with the help of beams. And denser virtual cathode creates deeper potential well.
You need the right distribution (by location) of electrons density in Polywell. This distribution can be described by number density or potential gradient.

So, other than the "beams" part, how does this contradict anything I have stated?

Oh and two things:
First: the potential well is typically anticipated to be 80% to 90% of the MaGrid (drive) voltage.
Second: Well depth doesn't have much to do with beta. Beta relates overall pressure to the magnetic field. This is a function of energy AND density of particles. The well depth is a function of the DIFFERENCE in the two species in the well.

A well that is made by 1E6 electrons and no protons will be the same well as one produced by 1001E6 electrons and 1E9 protons/deuterons... The PRESSURE from the second case will be MUCH greater.

[ladajo]

Joseph,
This is your sticking point:

Virtual cathode is created with the help of beams.

You do not need beams to to make the virtual cathode.

[Joseph Chikva]

Thanks, I know what Polywell is: Unlike fusor in which ions are attracting by negatively charged grid, Polywell is the machine attracting ions with the help of virtual cathode located in the center (so, location of electrons does matter).
Virtual cathode is responsible on creation of potential well.
Virtual cathode is created with the help of beams. And denser virtual cathode creates deeper potential well.
You need the right distribution (by location) of electrons density in Polywell. This distribution can be described by number density or potential gradient.

So, other than the "beams" part, how does this contradict anything I have stated?

Oh and two things:
First: the potential well is typically anticipated to be 80% to 90% of the MaGrid (drive) voltage.
Second: Well depth doesn't have much to do with beta. Beta relates overall pressure to the magnetic field. This is a function of energy AND density of particles. The well depth is a function of the DIFFERENCE in the two species in the well.

A well that is made by 1E6 electrons and no protons will be the same well as one produced by 1001E6 electrons and 1E9 protons/deuterons... The PRESSURE from the second case will be MUCH greater.

According to the article linked by Dan Tibbets potential of virtual cathode is only 14% and not 80-90% of the applied voltage. And as I remember you and MSimon told namely on potential well's depth.
If you want to speak about beta. We can talk about beta too.
As that's right: the well made by 1E19 electrons can confine more ions than 1E9 and will produce much pressure. But there is not any evidence and even mention of any numbers what real numbers were achieved. And the man who really built Polywell like reactor mentioned 2-stream and Wiebel instability. I assume that there is certain limit in achievable quantity of electrons creating well. That well confine ions. Those two spices produce gas pressure. And possible number of that pressure depends on the depth of well. That pressure will be MUCH lower than magnetic pressure and beta will be MUCH lower that 1. Due to instability. Kay?

[Joseph Chikva]

Joseph,
This is your sticking point:

Virtual cathode is created with the help of beams.

You do not need beams to to make the virtual cathode.

Who said you such thing?
Example:
http://adsabs.harvard.edu/abs/2001APS..DPPLO2011C

Properties of Forward Current Propagation beyond the Virtual Cathode
The high-current beam electrons inside the cavity create a virtual cathode...A virtual cathode is formed in a cavity, if the injection current from a diode exceeds the critical current...

Do you want more examples?

[KitemanSA]

According to the article linked by Dan Tibbets potential of virtual cathode is only 14% and not 80-90% of the applied voltage. And as I remember you and MSimon told namely on potential well's depth.

Hey dude, you read that BACKWARDS. The 14% is the amount of EXTRA you want to put into the electron drive in excess of the desired well depth. By these values, the well depth would be 1/1.14 of the drive, i.e., about 88%. Per the various publications by Bussard, there is a bit more loss. By the way, Miley is talking fusors and ION drive energy to ION well depth, but the concept remains the same.

From the definition of P(in), it is clearly of interest to inject ions with minimum energy above the well (E->E0) in order to obtain large gains from the system. However, there are limits to this, because the ion source distribution will always present some spread [embodied in the deviations σEs and σLs in Eq. (7)]. In this work, it is assumed that the ion injection kinetic energy over the top of the well is 4%–14% of the ion well depth.

If you want to speak about beta. We can talk about beta too.
As that's right: the well made by 1E19 electrons can confine more ions than 1E9 and will produce much pressure. But there is not any evidence and even mention of any numbers what real numbers were achieved. And the man who really built Polywell like reactor mentioned 2-stream and Wiebel instability. I assume that there is certain limit in achievable quantity of electrons creating well. That well confine ions. Those two spices produce gas pressure. And possible number of that pressure depends on the depth of well. That pressure will be MUCH lower than magnetic pressure and beta will be MUCH lower that 1. Due to instability. Kay?

Actually, a man that build the WB8 said that two stream instability was NOT a problem. I'll take his info over your suspicions. Tentatively.

Yet your concerns may indeed be what finally kills Polywell. We shall see. Tick, tock.

[rjaypeters]

"Repent, Harlequin!" Said the Ticktockman.

[Joseph Chikva]

According to the article linked by Dan Tibbets potential of virtual cathode is only 14% and not 80-90% of the applied voltage. And as I remember you and MSimon told namely on potential well's depth.

Hey dude, you read that BACKWARDS. The 14% is the amount of EXTRA you want to put into the electron drive in excess of the desired well depth. By these values, the well depth would be 1/1.14 of the drive, i.e., about 88%.

You are only juggling with numbers with lack of sense:

Theoretical and experimental studies of kinetic equilibrium and stability of the virtual cathode in an electron injected inertial electrostatic confinement device
Nebel, R. A.; Stange, S.; Park, J.; Taccetti, J. M.; Murali, S. K.; Garcia, C. E.
Physics of Plasmas, Volume 12, Issue 1, pp. 012701-012701-8 (2005).
This paper explores the electron-electron two-stream stability limit of a virtual cathode in spherical geometry. Previous work using a constant density slab model [R. A. Nebel and J. M. Finn, Phys. Plasmas 8, 1505 (2001)] suggested that the electron-electron two-stream would become unstable when the well depth of the virtual cathode was 14% of the applied voltage. However, experimental tests on INS-e have achieved virtual cathode fractional well depths ~60% with no sign of instability. Here, studies with a spherical gridless particle code indicate that fractional well depths greater than 90% can be achieved without two-stream instabilities. Two factors have a major impact on the plasma stability: whether the particles are reflected and the presence of angular momentum. If the particles are reflected then they are guaranteed to be in resonance with the electron plasma frequency at some radius. This can lead to the two stream instabilities if the angular momentum is small. If the angular momentum is large enough it stabilizes the instability much the same way as finite temperature stabilizes the two-stream instability in a slab.

I've remembered the first article, the abstract of wich linked by Dan and where is written

the electron-electron two-stream would become unstable when the well depth of the virtual cathode was 14% of the applied voltage.

Now I see 90% of applied voltage at the expence of large angular momentums. But what is large angular momentum my friend? This is thermalization that can not be large initially at once after switching on of reactor.

If you bother that something can kill Polywell I would recall you very nice idea of Nick Cristafilos's Astron that yes - was killed by presense of two-stream.
But that's not me but Laws of Nature. Sorry.

[hanelyp]

The potential well in a polywell is created by energetic electrons scattering off the boundary magnetic field into the interior, rather than collecting on that boundary, creating a volume of net negative charge density. How the electrons got into the interior of the wiffleball or gained their energy doesn't matter. No beam behavior is needed, and is actually as desired as a charged plasma in a tokomak. We =want= any beam like behavior of electrons coming in through a cusp to be disrupted.

[Joseph Chikva]

The potential well in a polywell is created by energetic electrons scattering off the boundary magnetic field into the interior, rather than collecting on that boundary, creating a volume of net negative charge density. How the electrons got into the interior of the wiffleball or gained their energy doesn't matter. No beam behavior is needed, and is actually as desired as a charged plasma in a tokomak. We =want= any beam like behavior of electrons coming in through a cusp to be disrupted.

Do not be so categorical.
As:
-I see that Dr. Nebel has investigated 2-stream instability. I did not know this before our current discussion. So, that is the problem (2-stream), which according to Nebel's words can be solved only with the presence of large angular momentums and, so, thermalization. And avoiding one problem of instability developers inevitably will come to another one - thermalization.
-There in your text are two oppositely mutually exclusive statements:
1. electrons scattering off the boundary magnetic field into the interior
2. wiffleball, that is as I understand the compact - much smaller than entire reactor zone clot of electrons, which impossible to create without of intersecting of several beams.

And I see that this discussion is entered in depth of theory.
I think that this is an answer on my statement that neither Polywell nor Helion did not leave the initial conceptual phase. And very unlikely that on base of their concepts practical reactor can be built in near future.
I am repeating that at this moment only TOKAMAK has left initial phase entering into enginnering phase.
Is this pleasant to you or not, but that's true.

[KitemanSA]

You are only juggling with numbers with lack of sense:

Theoretical and experimental studies of kinetic equilibrium and stability of the virtual cathode in an electron injected inertial electrostatic confinement device
Nebel, R. A.; Stange, S.; Park, J.; Taccetti, J. M.; Murali, S. K.; Garcia, C. E.
Physics of Plasmas, Volume 12, Issue 1, pp. 012701-012701-8 (2005).
This paper explores the electron-electron two-stream stability limit of a virtual cathode in spherical geometry. Previous work using a constant density slab model [R. A. Nebel and J. M. Finn, Phys. Plasmas 8, 1505 (2001)] suggested that the electron-electron two-stream would become unstable when the well depth of the virtual cathode was 14% of the applied voltage. However, experimental tests on INS-e have achieved virtual cathode fractional well depths ~60% with no sign of instability. Here, studies with a spherical gridless particle code indicate that fractional well depths greater than 90% can be achieved without two-stream instabilities. Two factors have a major impact on the plasma stability: whether the particles are reflected and the presence of angular momentum. If the particles are reflected then they are guaranteed to be in resonance with the electron plasma frequency at some radius. This can lead to the two stream instabilities if the angular momentum is small. If the angular momentum is large enough it stabilizes the instability much the same way as finite temperature stabilizes the two-stream instability in a slab.

Dude, did you even read what you quoted?

Bussard reports well depths of >80% drive voltage. Nebel states that WB7 didn't show any instability.

Who am I going to call, you, or them? THEM!!!

[KitemanSA]

2. wiffleball, that is as I understand the compact - much smaller than entire reactor zone clot of electrons, which impossible to create without of intersecting of several beams.

If this is you talking and not an unattributed quote, then you DO mis-understand the wiffleball.

And then there is the question of whether you are trying to insist there must be an instability issue because at the very initial instants while charging up a Polywell, there are beams intersecting at the center of the reactor.
Yes, at that very first instant of the start-up, there are beams intersecting at the center of the reactor. But of course, this would be BEFORE there is a wiffle ball and before the reaction has started, and as the wiffleball inflates, the beams disperse into a spray as soon as they enter INTO the wiffleball. Thus, in the OPERATING reactor, there are no beams, and thus no two beam instability.