Ground up theoretical explanation

[Professor Science]

I will preface this entire post with the fact that I am but a lowly undergrad student.

I am very interested in Polywell fusion reactors, and I've been paying attention, eagerly awaiting positive news on the peer review, for coming on two years now. the tricky thing is I don't feel like i have a respectable understanding of how the things work. I think I know, but I'm not terribly confident.

I was wondering if there was a place I could go where there is a ground up explanation. And I'm talking ground up, like maxwells equations, field lines and the right hand rule as ground level.

[MSimon]

I will preface this entire post with the fact that I am but a lowly undergrad student.

I am very interested in Polywell fusion reactors, and I've been paying attention, eagerly awaiting positive news on the peer review, for coming on two years now. the tricky thing is I don't feel like i have a respectable understanding of how the things work. I think I know, but I'm not terribly confident.

I was wondering if there was a place I could go where there is a ground up explanation. And I'm talking ground up, like maxwells equations, field lines and the right hand rule as ground level.

As far as I know there is nothing like that out there. Maybe the EMC2 folks have it. That would be the only place AFAIK.

Second best is studying the materials available at:

http://iecfusiontech.blogspot.com/

There are lots of links esp on the sidebar.

[drmike]

Dig through the pdf's here for some core equations. Then just start asking questions!

[TallDave]

Valencia is a good place for an overall theoretical framework. I've referenced it pretty often in discussing the topic.

http://www.askmar.com/ConferenceNotes/2 ... 0Paper.pdf

Polywell is fairly complicated, and there's often confusion about details of the device's operation even among those of us who have studied it a while.

Simon's and drmike's link are great for more detail.

[Professor Science]

Ok, here's my understanding. we have the polywell, which can be described as a cube faced with toroidal magnets, configured such that they generate opposing magnetic fields at the center of the cube. This configuration is what keeps electrons clustered majoritively near the center due to charges moving at right angles to field lines.

This concentration of electrons in the center causes the positively charged boron and hydrogen nuclei to charge into each other repeatedly like marbles in the bottom of a steep walled bowl. They ram into each other with enough force from coulombic attraction to fuse, and rapidly undergo 2 fissions, first 1 alpha and a jacked up carbon and then two more alphas. the alphas then fly out towards a grid wherein they deposit their kinetic energy.

things determined engineering problems: cooling surfaces at a rate of 1Mw/M^2
coils that do not get perforated when bombarded with high energy alpha's.
making steady state 2 T mag fields.

things that niggle at the back of my brain:
why do the effects of mag fields on the positively charged particles get ignored?

[93143]

This configuration is what keeps electrons clustered majoritively near the center due to charges moving at right angles to field lines.

Sort of. The moving electrons generate their own magnetic field opposing the applied field, which pushes back the applied field like an inflating balloon and results in a fairly large ball of electrons in which the field is effectively zero. This configuration is necessary to get the high-efficiency electron trapping effect; otherwise it would leak too fast out the cusps. The cusps don't go away in this configuration; they just get really small so that they don't leak much.

coils that do not get perforated when bombarded with high energy alpha's.

It isn't perforation that's the problem; it's sputtering/erosion, with the corresponding presence in the core of large amounts of eroded material which will either screw up the reaction balance (if it's fuel) or load up the plasma with nonreacting crud (if it's not fuel).

making steady state 2 T mag fields.

Shouldn't be that tough.

why do the effects of mag fields on the positively charged particles get ignored?

It isn't that large. Ions are MUCH heavier than electrons, so the field has less of an effect on them. Once you start to get up past 6 T or so, you might want to start considering it.

The main physics questions now are 1) is the confinement actually good enough? We should have some idea once the peer review is finished, but only a full-size machine can answer it definitively, and 2) what are the plans for mitigating ion-to-electron collisional power losses (either bremsstrahlung or loss of upscattered electrons) in the p-11B case, and will they work? That last one won't be answered for a while.

In the event p-11B proves unworkable, D-D should still be fine, and better than D-T in a tokamak. Assuming question (1) has a positive answer...

[blaisepascal]

This concentration of electrons in the center causes the positively charged boron and hydrogen nuclei to charge into each other repeatedly like marbles in the bottom of a steep walled bowl. They ram into each other with enough force from coulombic attraction to fuse, and rapidly undergo 2 fissions, first 1 alpha and a jacked up carbon and then two more alphas.

Correction: The p and B11 fuse to form a jacked-up C12, which alpha-decays into Be8, which splits into two alphas.

[TallDave]

why do the effects of mag fields on the positively charged particles get ignored?

Nebel has noted the Larmor radius is infinite over most of the area of the interior.

This configuration is what keeps electrons clustered majoritively near the center due to charges moving at right angles to field lines.

It's a dynamic picture, because there's a constant feed of electrons, and some electrons are always being lost to cross-field transport, chamber walls, or unshielded Magrid surfaces, as well as recirculating through cusps. It might be more accurate to say the electrostatic well focuses at the center, though focussing may not be especially important given the densities envisioned.

Also, I'm not 100% on this, but I think they were looking at magnets around 5T.

[tombo]

Is that 5T at the coil center point or at the coil surface?

[drmike]

Center bore is usually what it refers to. In a Helmholtz configuration it's the center between 2 coils. For an MRI machine, it's on axis center bore. Sticking with that makes the most sense (i.e. center of coil).

[tombo]

That's what I thought. But since I have seen here numbers ranging from maybe 0.1T to 10T or so, I thought different people may have been calling it at different locations. But it's really just the uncertainty in our understanding of the process.

[jlumartinez]

Try downloading this ebook in PDF about Polywell. You could find some in-depth foundations and some recent history:

http://www.polywellnuclearfusion.com/Cl ... ywell.html

[Professor Science]

Center bore is usually what it refers to. In a Helmholtz configuration it's the center between 2 coils. For an MRI machine, it's on axis center bore. Sticking with that makes the most sense (i.e. center of coil).

Magnetic field in a superconductor is always zero, one of their nifty properties. Meissner effect and all. So center bore can't refer to inside the coil, can it?

[drmike]

You are correct. "Center bore" means the axis around which the coil is wound. You are thinking center of the wire, which is a different "center"!

The peak field along the axis in the center of a magnet is usually the most useful to work with. It tends to be more uniform, so approximations work well there. It is just a matter of convention.

[icarus]

Professor Science:

Ok, here's my understanding. we have the polywell, which can be described as a cube faced with toroidal magnets, configured such that they generate opposing magnetic fields at the center of the cube. This configuration is what keeps electrons clustered majoritively near the center due to charges moving at right angles to field lines.

I think you've missed the major point that the toroidal magnetic coils are actually positively charged electrodes that attract a surrounding "sheath" of electrons. The development history is that the magnetic field was innovated to shield the electrodes from the electron cloud it attracts.

The secondary effect of a virtual electrode electron cloud forming in the center of the device is what makes it a proposed type of IEC fusion (if it does indeed cause fusion).

A tertiary effect is the pushing back of the magnetic field by the electron cloud in the center: inflating the magnetic void in the center (or perhaps even creating a field inversion/reversal in this area), into a "wiffle-ball" cavity that has some special confinement properties, yet to be determined experimentally but theoretically different from a typical cusp confinement device.