Spheroidal Foci and POPS?

[Art Carlson]

Sorry. I have neither the time nor the inclination to go through the whole thing again. To give you a brief reminder: The loss fans will be quasi-neutral. Tell me about the energy losses via the ions.

Perhaps I'm confused (I say that a lot), do you mean the cusp losses when you mention loss fans?

Yes.

I believe this would imply ambiploar cusp flows, which R. Nebel disputed.

No. Quasineutrality does not imply ambipolarity.

I don't understand all the details of why ions that do escape carry away only tolorable system energy, but it is a claim. I also do not understand how injected ions are introduced below the Wiffleball border unless there is some mechanism to bleed off some of thier initial radial potential energy.

Rider also mentioned this a few times as an unsolved problem.

... I believe the cusps are not ambipolar overall because ...

Do you mean that the cusp plasma is not quasineutral, or that the cusp losses are not ambipolar?

[Art Carlson]

Because the loss fans/beams extend beyond the magrid, the ions in them will be accelerated to the walls.

The walls are almost as positive as the magrid. Why would the ions go there?

Electrons exit the large holes along the magnetic field lines in six jets, at very low radial velocity, are caught by the (relatively) positive charge on the magrid and recirculated back to the wiffleball.

Sorry, but I don't have time to point out all your contradictions. You're on your own.

[alexjrgreen]

You are welcome to fix that problem first, if you like.

Modelling the jets as a tubular sheet of electrons with a rounded cap, at the end nearest the wall the ions are going to be outside the electron sheet because they take longer to slow down.

Along most of the tube, though, they're going to be inside the electron sheet because of the charge on the magrid.

[alexjrgreen]

Sorry, but I don't have time to point out all your contradictions. You're on your own.

The magnetic field, the difference in mass between the electrons and the ions, the charge on the magrid and the geometry of the system all make it impossible for the electrons and the ions to follow the same paths.

Even with (slightly electron rich) quasi-neutrality, the ions and electrons cannot be in the same places.

[alexjrgreen]

The walls are almost as positive as the magrid. Why would the ions go there?

Sorry, but I don't have time to point out all your contradictions.

OK. My ill-judged sarcasm backfired.

Seriously, though. The walls are at ground, so if the ions can see electrons on the outside of the electron jets, why would they go to the wall?

In fact, the ions which fan out of the end of the electron jet come back in through the sides and collide with the ions going out. It's quite likely that fusion occurs there.

[TallDave]

In fact, the ions which fan out of the end of the electron jet come back in through the sides and collide with the ions going out. It's quite likely that fusion occurs there.

It's not likely ions ever get out that far (Luis Chacon is apparently pretty confident about this). The plasma in a Polywell is only generally quasineutral. The fact we're pumping in more electrons than ions means electrons are being pushed out of the plasma into the cusps; because of the well, electrons dominate the edges and cusps while ions are focused at the center.

Art has a different picture in which upscattered ions are streaming out the cusps in large numbers. This either contradicts WB-7 results, or Dr. Nebel's team couldn't measure that loss and the Navy review board approved the $12M WB-8 and asked for a WB-9 100MW reactor design anyway. I know which way I'm leaning but we can choose to believe what we like until such time as we have better information.

[alexjrgreen]

In fact, the ions which fan out of the end of the electron jet come back in through the sides and collide with the ions going out. It's quite likely that fusion occurs there.

It's not likely ions ever get out that far (Luis Chacon is apparently pretty confident about this). The plasma in a Polywell is only generally quasineutral. The fact we're pumping in more electrons than ions means electrons are being pushed out of the plasma into the cusps; because of the well, electrons dominate the edges and cusps while ions are focused at the center.

The greatest density of ions is in the centre, but that's because of the spherical topology. They spend half their time outside the wiffleball slowing down and turning round.

Art has a different picture

If Luis Chacon were right, Rick would surely already know how the Polywell scales. Somewhere in Art's brilliant but Tokamak-distracted brain is the key to how a Polywell really works, if only I can persuade him to look at it with a fresh pair of eyes.

[Art Carlson]

It's not likely ions ever get out that far (Luis Chacon is apparently pretty confident about this).

Chacon made no such statement. He calculated a spherically symmetric system. No cusps.

The plasma in a Polywell is only generally quasineutral.

What does that mean? "Generally neutral" or "only quasineutral"? "Quasineutral" is a quantitative statement. You can calculate for a given geometry, density, and potential the value of (Z*n_i-n_e)/n_e

[alexjrgreen]

The plasma in a Polywell is only generally quasineutral.

What does that mean? "Generally neutral" or "only quasineutral"? "Quasineutral" is a quantitative statement. You can calculate for a given geometry, density, and potential the value of (Z*n_i-n_e)/n_e

The electron plasma contained by the Polywell magnetic field doesn't start out quasi-neutral. The wiffleball is formed before the ions are introduced.

[MSimon]

In fact, the ions which fan out of the end of the electron jet come back in through the sides and collide with the ions going out. It's quite likely that fusion occurs there.

It's not likely ions ever get out that far (Luis Chacon is apparently pretty confident about this). The plasma in a Polywell is only generally quasineutral. The fact we're pumping in more electrons than ions means electrons are being pushed out of the plasma into the cusps; because of the well, electrons dominate the edges and cusps while ions are focused at the center.

Art has a different picture in which upscattered ions are streaming out the cusps in large numbers. This either contradicts WB-7 results, or Dr. Nebel's team couldn't measure that loss and the Navy review board approved the $12M WB-8 and asked for a WB-9 100MW reactor design anyway. I know which way I'm leaning but we can choose to believe what we like until such time as we have better information.

I still favor 100 mW as the minimum design goal. I expect a minimum of 1 W. Operation at higher powers may only be momentary if the shielding is minimal.

That is three orders of magnitude up from 100 uW (WB-6 estimates) - so engineering wise I'd say it makes sense. Esp if going from a pulsed to continuous operation machine.

[D Tibbets]

Sorry. I have neither the time nor the inclination to go through the whole thing again. To give you a brief reminder: The loss fans will be quasi-neutral. Tell me about the energy losses via the ions.

Perhaps I'm confused (I say that a lot), do you mean the cusp losses when you mention loss fans?

Yes.

I believe this would imply ambiploar cusp flows, which R. Nebel disputed.

No. Quasineutrality does not imply ambipolarity.

I don't understand all the details of why ions that do escape carry away only tolorable system energy, but it is a claim. I also do not understand how injected ions are introduced below the Wiffleball border unless there is some mechanism to bleed off some of thier initial radial potential energy.

Rider also mentioned this a few times as an unsolved problem.

... I believe the cusps are not ambipolar overall because ...

Do you mean that the cusp plasma is not quasineutral, or that the cusp losses are not ambipolar?

My understanding of quasineutrality is limited and suffers relapses, but as in this link, I understand a neutral plasma on large scales can have local non neutral distributions of charged particles on small scales based on the Debye length (actually ~10X Debye length). In a Polywell the core might have a Debye length of a few mm or less (?), while near the cusp regions it might be ~ up to 1 cm. I think this means that (unless you broke quasineutrality) significant charge variation could only occur over scales of ~ 10 cm or more. Probably less as the 1 cm figure comes from the density in low Earth orbit, and I do not think the density in the cusp regions need be that low. This scale within a WB6 sized machine would be difficult to achieve in the Wiffleball average distance to magrid diameter space, but in a several meter wide machine there is much more leeway, Of course in the Pollywell you do not start out with a neutral plasma on the large scale, which is possible because of the limited excess of electrons and efficient electron trapping (and the claimed final necessary energy balance margin from electron recirculation). Or as the size of the Polywell increases, the limitations of quasineutrality and related ambipolar flow constraints become more relaxed. I'm guessing that this may be an instance in which scaling up the machine size would be expected to improve performance, or at least reduce concerns about B^4 R^3 scaling predictions.

http://www.plasma-universe.com/index.ph ... neutrality

The link below gives an argument of how ambipolarity is driven by the need to prevent too much charge separation in a neutral plasma. But in the polywell the plasma has an electron excess so this effect in free space is biased towards more electrons leaving the volume than ions, ie, so long as you pump excess electrons into the system, there would not be ambipolar outflow. In a spherical cusp system like the Polywell I believe the results would be the same, though with perhaps complications.

http://en.wikipedia.org/wiki/Ambipolar_diffusion

Dan Tibbets

[alexjrgreen]

In a spherical cusp system like the Polywell I believe the results would be the same, though with perhaps complications.

http://en.wikipedia.org/wiki/Ambipolar_diffusion

Dan Tibbets

Dan,

The pictures of the permanent magnet polywell in your pressure cooker seem to show a spherical grid cathode. Do you have an electron gun for it?

MSimon can probably suggest the cheapest vacuum tube to break to get one...

Given the success of your first attempt, it would be interesting to set up a wiffleball without the grid.

[D Tibbets]

In fact, the ions which fan out of the end of the electron jet come back in through the sides and collide with the ions going out. It's quite likely that fusion occurs there.

It's not likely ions ever get out that far (Luis Chacon is apparently pretty confident about this). The plasma in a Polywell is only generally quasineutral. The fact we're pumping in more electrons than ions means electrons are being pushed out of the plasma into the cusps; because of the well, electrons dominate the edges and cusps while ions are focused at the center.

The greatest density of ions is in the centre, but that's because of the spherical topology. They spend half their time outside the wiffleball slowing down and turning round.

Art has a different picture

If Luis Chacon were right, Rick would surely already know how the Polywell scales. Somewhere in Art's brilliant but Tokamak-distracted brain is the key to how a Polywell really works, if only I can persuade him to look at it with a fresh pair of eyes.

As far as the ions turning around beyond the Wiffleball border, I think that depends on your definition of the Wiffleball and the shape of the potential well. If the Wiffleball is dependent on the electron density and vectors only , then yes. If the ions are contributing to the Wiffleball expansion, then it is more complex. With a square potential well (essentially, the electrons considered mostly confined to an area equal distance from the core- a shell?)this would be true. If the potential well is eliptical, the electrons spend most of their time in a gradient, densest near the center and least dense near the border. This would require the electrons to maintain mostly radial paths (nonthermalized) with slow speeds near the converged center and high speeds near the border as they reach the turnaround point (Wiffleball border). Assuming the average ion has a maximal potential energy derived from the electron gradient, and any central virtual anode is not to great, it may actually turn around before reaching the Wiffleball border. Again, I don't know how ions could be injected at these levels without screwing things up. I can see the attractiveness of neutral gas input to do this. The neutrals would not begain ionizing untill they reached the electrons within the Wiffleball border. Also, they would not need to be injected through a cusp, which I assume can only complicate the cusp flows and recirculation in that cusp.

Concerning fusions outside the magrid, I would not expect much as the escaping ions are traveling mostly parrellel to each other as they exit the cusp, near head on collisions (beam- beam collisions) would be rare (unless you use an approach which I have been ruminating about). Also, the ions should be traveling at low speeds, the sum of their upscattered escape speed, plus the accelerating charge on the magrid, minus the decellerating charge of the potential well multiplied by some number related to the inverse square law(?).

Also, rember the vacuum vessel wall, irregardless of charge is essentially invisible to the internal ions, untill they hit it, Gauss's Law again.

Dan Tibbets

[alexjrgreen]

As far as the ions turning around beyond the Wiffleball border, I think that depends on your definition of the Wiffleball and the shape of the potential well. If the Wiffleball is dependent on the electron density and vectors only , then yes. If the ions are contributing to the Wiffleball expansion, then it is more complex.

I've always understood the term "wiffleball" to be a like for like description - a hollow sphere with holes in it. That would refer to the magnetic containment of electrons to form a virtual grid.

I've not seen any suggestions that the ions contribute to the formation of the wiffleball, only that enough of them cause it to collapse.

[MSimon]

In a spherical cusp system like the Polywell I believe the results would be the same, though with perhaps complications.

http://en.wikipedia.org/wiki/Ambipolar_diffusion

Dan Tibbets

Dan,

The pictures of the permanent magnet polywell in your pressure cooker seem to show a spherical grid cathode. Do you have an electron gun for it?

MSimon can probably suggest the cheapest vacuum tube to break to get one...

Given the success of your first attempt, it would be interesting to set up a wiffleball without the grid.

It depends on the amount of cathode current needed. 6L6s and variants are common for the 100 ma or so range. A 12AX7 or 12AT7 is good in the 10 ma range. The versions made by the Soviets (now Russians) are considered good and not too expensive.

The difficulty I see is that they are linear and not point sources. Some collimation may be required. and that complicates things.

Thoriated tungsten wire may be a better bet.

Tom Ligon used filamented auto headlights as emitters.