2011 IEC Confrence slide presentations are now up

[KitemanSA]

X ray losses are losses only if the energy is not recovered. Just as with neutrons or non direct converted fast fusion ions, the energy ends up as heat in the walls. This is carried away by a coolent, and runs a steam turbine to harvest this heat (both from fusion, x-rays, fuel ion and electron losses). The problem is that this thermal energy can be converted to electricity at only ~ 25-30% efficiency.

Such efficiencies are usually found only in lower temperature systems (typical nukes for instance). 40-44% are not unheard-of in high temperature coal-fired plants.

[choff]

It would be ironic of Joel's patent got approved after all the grief EMC2 had. Would that mean Park would have to get a license from Joel Rogers to continue his research.

The Riggatron might be the only practical tochamak design that never got major funding, unlike ITER. If I was in the oil industry and wanted to bury Polywell fusion, I'd have all the funding go to a giant impratical version with a few bugs introduced, let the small version gather dust.

[TallDave]

IIRC he did mention some cusp-plugging effects in past presentations.

Yes, but cusp plugging didn't work. Not the same thing as the wiffleball.

Didn't work in what respect? IIRC he did see the effect.

Cusp-plugging is an aspect of the WB: the shape of the field lines at beta=1 creates a long throat that gets plugged with cold electrons at the center -- at least, that was the last best understanding I saw on the topic. (Art never liked the idea because he thought it would pull in ions, but I think Joel has proved his treatment was much too simplistic.)

Tom suspected he saw cusp-plugging in PZL-1, and I believe Rick was eyeing it as well.

[TallDave]

also i'm still a little skeptical about how you can maintain a small excess of electrons in the plasma at high confinement. you can get net neutral plasma through neutral gas puffs, sure. but magnetic electron confinement is a two-way street: it keeps electrons out just as well as it keeps them in.

The electrons are either inserted within the WB, or along field lines at the cusps. Presumably they behave stochastically inside.

[TallDave]

That is way too large for use in a fusion powered rocket... Perhaps using D-D (and dealing with the neutronic mess) rather than pB11 would allow for a small enough reaction chamber to use in an interplanetary rocket.

Compared to chemical rockets, yes. Compared to a fission rocket...

http://en.wikipedia.org/wiki/Project_Or ... pulsion%29

I would think you would want to use D-D outside Earth orbit though, you get a lot more power at the same conditions that way.

[happyjack27]

also i'm still a little skeptical about how you can maintain a small excess of electrons in the plasma at high confinement. you can get net neutral plasma through neutral gas puffs, sure. but magnetic electron confinement is a two-way street: it keeps electrons out just as well as it keeps them in.

The electrons are either inserted within the WB, or along field lines at the cusps. Presumably they behave stochastically inside.

yeah, that's just the thing: as containment gets better, the cusps get smaller.

[KitemanSA]

IIRC he did mention some cusp-plugging effects in past presentations.

Yes, but cusp plugging didn't work. Not the same thing as the wiffleball.

Didn't work in what respect? IIRC he did see the effect.

Cusp-plugging is an aspect of the WB: the shape of the field lines at beta=1 creates a long throat that gets plugged with cold electrons at the center -- at least, that was the last best understanding I saw on the topic. (Art never liked the idea because he thought it would pull in ions, but I think Joel has proved his treatment was much too simplistic.)

Tom suspected he saw cusp-plugging in PZL-1, and I believe Rick was eyeing it as well.

As I understand the lingo, wiffleball effect and "cusp plugging" are different concepts. IIRC, in the WB5 design, EMC2 installed a chargfed plate to plug the electron flow out the cusps. That didn't work.

But then again, the "self plugging" that happens with a wiffle-ball is new to me.

Isn't it great! Still learning after all these years!

[D Tibbets]

X ray losses are losses only if the energy is not recovered. Just as with neutrons or non direct converted fast fusion ions, the energy ends up as heat in the walls. This is carried away by a coolent, and runs a steam turbine to harvest this heat (both from fusion, x-rays, fuel ion and electron losses). The problem is that this thermal energy can be converted to electricity at only ~ 25-30% efficiency.

Such efficiencies are usually found only in lower temperature systems (typical nukes for instance). 40-44% are not unheard-of in high temperature coal-fired plants.

Conceded. My understanding of Brayton steam cycles is limited. Use of of ~ 550 degrees C steam heat without going to exotic high cost metal allows is a decision that I understand limits typical efficiencies to ~ 25-30%. It also depends on the the effort exerted to extract the last traces of useful heat in the steam after it passes through the high pressure and low pressure steam turbines. The additional possible gains are competing with increased costs. I understand that natural gas plants may be more efficient than coal fired plants- I''m uncertain why.

Dan Tibbets

[MSimon]

It would be ironic of Joel's patent got approved after all the grief EMC2 had. Would that mean Park would have to get a license from Joel Rogers to continue his research.

The Riggatron might be the only practical tochamak design that never got major funding, unlike ITER. If I was in the oil industry and wanted to bury Polywell fusion, I'd have all the funding go to a giant impratical version with a few bugs introduced, let the small version gather dust.

The bug is major and everyone knows where it is: the neutron economy. At theoretical the device makes 10% more neutrons than it needs. And no one knows if a practical device can get above unity with such small margins.

[D Tibbets]

IIRC he did mention some cusp-plugging effects in past presentations.

Yes, but cusp plugging didn't work. Not the same thing as the wiffleball.

Didn't work in what respect? IIRC he did see the effect.

Cusp-plugging is an aspect of the WB: the shape of the field lines at beta=1 creates a long throat that gets plugged with cold electrons at the center -- at least, that was the last best understanding I saw on the topic. (Art never liked the idea because he thought it would pull in ions, but I think Joel has proved his treatment was much too simplistic.)

Tom suspected he saw cusp-plugging in PZL-1, and I believe Rick was eyeing it as well.

As above except- My limited understanding is that if there was a collection of cold electrons in the middle of the cusp for what ever reason- cusp plugging, then this acts as an attractive sink for ions, and Bussard essentially said this regarding WB5.
But, I believe this is different in the spaced recirculating condition of WB6. You do not have something that is pushing the electrons back in, or stopping them in the middle of the cusp, but you have the electron attractive charge on the magrid, slowing, then reversing escaping electrons well past the mid line of the cusp. It is a matter of position and 'lumpyness' With the stream of electrons slowing then reversing outside the central cusp region, there is greater distance between these electrons and the ions that are at the top of their potential well near the Wiffleball border. Because of the inverse square law, the distance of the separation is very significant. In a sense it is not the presence of repellers (or attractors) that is critical, but their position.

I think a classical repellar would have a problem stopping and reversing electrons (without distorting the critical magnetic fields)as they are fanning out from the cusp- thus placement in the center of the cusp where they are a much more attractive target for ions, but the attractor magnetically shielded magrid would not suffer from this complication. It is already an integral part of the magrid. *

You are pulling the electrons back in as opposed to pushing them back in. A subtle difference, but it allows for modification of the radial distance of much of these electrons relative to the cloud of ions. Also since the electrons are hot in the center of the cusp, their dwell time is less and this contributes to the cumulative effects
Thus there is not a collection of cold electrons in the center of the cusp that can pull out ions, The electrons remain hot (either in the inward or outward direction, until they pass the mid plane of the magrid, and even then the population of electrons will be spreading out depending on their escape velocity.

J Rogers mention of down scattered electron 'scrapers' outside the magrid is an element that seems unnecessary. My perhaps confused impression, is that any down scattered electron will still exit the cusp because of the internal space change, and once past the mid plane of the magrid it will be accelerated by the positive charge on the magrid to the full drive potential inward. This is due to another aspect of Gauss's law. With an infinite plane (or close enough) charged plate, a charged particle will be accelerated to the full potential irregardless of it's starting position above the plate. So long as the up scattered electrons has not reached escape velocity (exceeded the drive voltage) they will eventually reverse- or circulate through another cusp, or hit something. I would think if a scrapper was needed it would be for excessively up scattered electrons so that they are removed from the system. This is mentioned in the 2008 EMC2 patent application when they mention the limit on the distance of the tank walls outside of the magrid. If you have a direct conversion grid for the fusion ions, I could see a need for eliminating these up scattered electrons before they reach the conversion grid.

*The bridges, nubs, between the magnets of WB7 was reported as hot spots. If the spacing between the magnets is optimized (mentioned in the Sidney U. presentation) the electron losses in this close linear/ funny cusp regions is minimized, but still it is a sink for electrons right in the mid plane (or barely outside the mid plane) and with some magnetic shielding, electrons could collect here (cold electrons?) and act much as a formal repellar as in WB5. This attracts ions. The heating/ loss concerns Nebel expressed may have involved ion losses as well as electron losses. Thus another reason for wall standoffs instead of nubs between the magnets.

Dan Tibbets

[TallDave]

I think it would pull the ions, except for the geometry (which is why the WB effect is much more pronounced as the cusp is "squeezed"). Once again here the opposite energy profiles of the ions and electrons comes into play -- the slow ions at the edge would love to get down to the slightly negative hump of cold electrons piling up there around their respective "bottom" at the center of the Magrid frame, but the gradient begins far enough beyond the ions' average apogee that few make it to the promised land and so instead they bang into each (high collision cross-section) and tend to maxwellianize at low energy before heading back toward the core. The fast electrons, meanwhile, can shoot right in, mostly bouncing off the negative area and coming back in.

It's a bit like the virtual anode at the core, if that makes sense.

Maybe we'll actually get to see a detailed potential map someday.

[D Tibbets]

Everything TallDave said is true, but that is not the issue. The ions stope at the tope of their potential well. This is the electrostatic confinement. The magnetic cusps are an addition restraint on the ions ability to escape, but it is not the dominate confinement means as it is for the electrons. The electrostatic confinement is dependant on space charge/ local collision considerations. If there are two simple space charges to consider. One central to the ion and one outside the ion the effect will be due to an interaction between the two. Simplifying- point charge A of -10,000 volts located to the left of an ion at a distance of 1 Meter. Point charge B to the right of the ion with a voltage of 1000 Volts and a distance of 0.2 meters. And Point charge C to the right of the ion with a voltage of 1000 Volts, and a distance of 0.5 meters. Appliying the inverse square law results in Point a having an attractive force of 10,000V *1M^2 = 10,000 units
Point B = 1000 V * 1/ (0.2^2) = 1/ 0.04* 1000V= 50,000 units
Point C= 1000V * 1/(0.5 M^2) = 1000V * 4000 unit.

If a repeller resulted in a collection of electrons/ space charge in the middle of the cusp, any ion in this situation would be attracted towards point B. Provided it is at a cusp region, the ion will exit due to electrostatic considerations. If the net space charge effect of the electrons are at point C then the ion will still be attracted towards the center. It will still be electrostatically confined.

Remember, magnetic confinement is not very good. Not only can it escape through a cusp under electrostatic means, it can also transport theough the magnetic field. The whole point of the Polywell is that this magnetic shortcoming in ion confinement is overcome through electrostatic confinement, and in the above conditions the electrostatic confinement is greatly hindered if not reversed in these border regions if there are too many electrons accumulating in a cusp, especially if they are in the proximal portions of the cusp.

Dan Tibbets

[KitemanSA]

Such efficiencies are usually found only in lower temperature systems (typical nukes for instance). 40-44% are not unheard-of in high temperature coal-fired plants.

Conceded. My understanding of Brayton {should be Rankine, ed.} steam cycles is limited. Use of of ~ 550 degrees C steam heat without going to exotic high cost metal allows is a decision that I understand limits typical efficiencies to ~ 25-30%. It also depends on the the effort exerted to extract the last traces of useful heat in the steam after it passes through the high pressure and low pressure steam turbines. The additional possible gains are competing with increased costs. I understand that natural gas plants may be more efficient than coal fired plants- I''m uncertain why.

OMG, now we are going WAY back.
IIR my thermo correctly, there are two factors at work. First, Brayton cycles are closer to the ideal Carnot cycle than Rankine. Second, if you burn the natural gas IN the working gas, the temperature can be much higher than if you try to heat the gas thru a HEX.
There is some indication that a coal fired supercritical CO2 Brayton Cycle could be even better than the 44% they get with superheated / supercritical H2O Rankines. Things are improving.

[ladajo]

We are not going to re-visit thermo again are we???

[mvanwink5]

Remember, magnetic confinement is not very good.

Dan Tibbets

Dan,
High B fields will provide high ion/electron densities and recirculation, provided by the electrostatic confinement, takes care of the leaky magnetic field. So, once again I don't understand why Joel's simulation is at relatively low magnetic fields and his patent examples use low magnetic field copper magnets. It would seem he is discounting the size advantage of higher B fields and goes for a large radii polywell instead.

Best regards,