POPS iec fusion

[bennmann]

http://www.lanl.gov/p/rh_pp_park.shtml

Can someone please explain that (POPS fluctuation) to me in layman's terms (or just significantly more detail), preferably with MSPaint pictures included?

[MSimon]

POPS is about applying RF (tuned to the plasma) to increase the density at the point of beam collision.

More on the sidebar at IEC Fusion Technology

[bennmann]

Cool! Close enough to what I was looking for!

The Wikipedia page doesn't have as good sources as you do

[KitemanSA]

Sounds like you have some wiki-work to do!

[happyjack27]

i thought it was oscillating the driving current to resonate with the ion transit, so as to reduce radial maxwellianization, in addition to oscillating between a low and high well depth, thus having a higher peak well depth.

in anycase if its not i think that might be a good idea.

[D Tibbets]

My understanding of POPS is marginal at best, but one beneficial effect is possibly to bring all of the ions together in the center at once. Beams that intersect in the center contain an ~ even distribution of ions along their lengths, so only a small portion of them are passing through the center at any time and thus few ions can interact with other beam ions at any finite amount of time. POPS bunches these ion streams into local groups, and these groups reach the center at the same time, so many more ions can collide and fuse during any one oscillation. This effectively increases the density in the center, and as fusion rate scales as the density squared...

Dan Tibbets

[chrismb]

i thought it was oscillating the driving current to resonate with the ion transit, so as to reduce radial maxwellianization,

An outstanding observation for a 'newbie' to make. Yes, indeed, this is totally critical to getting a net-energy machine working.

Higher densities at the centre is the explanation fed into general consumption, as it is easy to understand. But it is meaningless if it is not efficient.

If you have a device that looses 90% of its input energy to thermalising behaviour, then increasing the reaction rate by x 100 with x 10 density input (if that were the case.. caveats pending...) then it just means that you loose 10 x that 90% of input power!

If you always loose at poker, then playing 10 games simultaneously just means you loose 10 times faster, y'see!

Yeah, dead right. POPS may hold a means to reduce thermalisation losses. Hat-tip to H'Jack.

[D Tibbets]

I'm not sure radial thermalization is the issue addressed (at least primarily) by POPS. I don't think that would change the central density much through that mechanism. It might vary the core size some , but this would be pulsating. And, in EMC2 papers, the transverse or angular momentum thermalization seems to be the major determinate of ions being lost to the core. As Nebel said, the core convergence is not critical to the Polywell working (though it would take a larger machine to reach the same net power*). The key (as I understand it) is the bunching of the ions into spherically converging waves so that ideally all of the ions reach the core at the same time. The core is not necessarily smaller, but the density within the core as this wave of particles converge is potentially much higher. Nebel has mentioned a possible gain of up to ~ 100X during this interval. I don't know if he was referring to the density or the resultant fusion rate (square of the density).

I think most of the work with POPS has been done with tuned microwave induced POPS effects. Varing voltage or magnetic fields may also work, but I suspect they might be more difficult and might (?) be more likely to adversely effect confinement.

* POPS effects might be irrelevant in the Polywell. If the size of the machine is limited by thermal wall loading issues, the addition of greater fusion efficiency may not have any advantage, at least in a thermal steam conversion system. In a P-B11 system, if most of the velocity could be imparted to the protons while the borons remain at relatively slow speeds, you might gain on Bremsstrulung losses. This might be done with microwaves tuned to the proton , though I don't know if this would be considered as a POPS effect.

Dan Tibbets

[happyjack27]

... The key (as I understand it) is the bunching of the ions into spherically converging waves so that ideally all of the ions reach the core at the same time...

that's what i meant when i said "...so as to reduce radial maxwellianization"; i meant inducing "spherically converging waves" through harmonic effects, such as RF / microwaves or as i suggested oscillating the drive current. "spherically converging waves" are by definition less radially maxwellianized.

though i was focusing on the implications of the speed and location being better synchronized, rather than as you mentioned, a higher peak density. a "double-whammy", it appears.

not sure what to do about axial thermalization. but i would think that the better radial synchronization would help to reduce that, as well. possibly quite strongly.

[D Tibbets]

True, the particals need to be at ~ the same speed to minimize thermalization effect. But, you can have a stream of ions traveling back and forth in an even distribution within the beam (no bunching). But this is not necessarily a Periodic Oscillation Plasma. It would be a monoenergetic smooth oscillating plasma. It is the synchronized periodic bunching of particles interacting in the center that I believe is necessary to boost the fusion rate. The radial thermalization issues have more to do with keeping the ions at the optimum speed for fusion, while reducing loss mechanisms (like Bremsstrulung, low speed ions that do not contribute to the fusion rate, or high speed ions that escape faster and carry away more wasted input energy). These radially upscattered ions are also more likely to be turned at an angle when they bounce off the surrounding convex magnetic surfaces (if they do not hit a cusp and escape), rather than straight back when they reach the top of the potential well. This increases angular momentum and leads to less convergence.

The dominate mechanism for controlling radial thermalization is the claimed annealing process. As the ions near the top of the potential well just inside the Wiffleball border, they are traveling the slowest. And at these low speeds (energies) the coulomb crossestion goes way up. The jostling of the ions in these local conditions quickly thermalizes them - BUT, at this low energy the Maxwellian distribution is much lower (eg: temp of 100 eV +/- 50 eV. This is a large spread, but when the ions fall back down a perhaps 10,000 V potential well, the speed would be 10,000 +/- 50 eV) The relative resultant thermalization is much less and this restoring process is continuous with each oscillation. and apparently dominates over the radial scattering occurring deeper in the machine

Dan Tibbets

[ladajo]

It would be a monoenergetic smooth oscillating plasma. It is the synchronized periodic bunching of particles interacting in the center that I believe is necessary to boost the fusion rate

Makes me think of lasing.

[TallDave]

I wonder if they're doing any POPS research on the WBs.

I'm still a bit fuzzy on this, but I'm assuming the headlight emitters don't give one sufficient control to modulate the velocity distribution of injected electrons. Maybe someone else can say more on how likely it is they are doing POPS now, at least in terms of what equipment they would need.

[chrismb]

I wonder if they're doing any POPS research on the WBs.

I'm still a bit fuzzy on this, but I'm assuming the headlight emitters don't give one sufficient control to modulate the velocity distribution of injected electrons. Maybe someone else can say more on how likely it is they are doing POPS now, at least in terms of what equipment they would need.

For precisely the same reason for your hazyness, I think WB could not do any POPS, it would have to be a fixed central electrode.

[happyjack27]

i would think that in the latter stages of testing they would at least do a little experimentation with RF and maybe oscillating the magnetic-field strength. they can certainly try it out and see what happens. (though i think w/oscillating the magnetic field strength they'd have to be careful to keep it in reasonable limits so as not to damage anything)

i'd certainly be curious if i were them, and if it could possibly multiply the fusion rate, it would certainly be worth the effort, time and money permitting. after other, more critical testing is done first, of course.

[happyjack27]

here's a very good post on the subject i found: http://www.polywellnuclearfusion.com/Cl ... /POPS.html

it sounds to me like they're gonna try it.