Thoughts about reactor packaging

[timothy.d.power]

This long-time lurker noted with great interest the recent predictions that the high-energy alphas would be deflected by the MaGrid's magnetic field (if the field were strong enough) and would escape through the cusps.

Most of the commentary on the earlier threads had to do with how this affects the first-wall problem, or how this affects ion injection, or how this affects the electrons in the polywell (and whether the stream of out-going alphas through the cusps create a virtual electrode to help the electrons escape).

But ravingdave made an interesting observation that I think needs expanding: knowing where the alphas leave the polywell greatly simplifies the problem of alpha collection. After a little thought, it seems to me that it allows the overall reactor (of which the polywell is just the core) to have a different shape than merely spherical--which may make it easier to package a hypothetical reactor onto an aircraft, or a locomotive.

Here's what I mean. I remember reading someone's BOE calculations in a previous thread that all the layers of a reactor--the polywell itself, and the decelerator grid, and the collector grid, with everything properly spaced--would have a diameter something like five meters.

But consider what would happen if the polywell core were shaped like an octahedron, with the alphas emerging only through the cusps in the faces of the octahedron. Then you would have eight evenly-spaced beams of alphas. Conceptually (and ignoring the problems of cubically-shaped vacuum chambers, for the moment), one could place this octahedron in the center of a cubic vacuum chamber, with each polywell face pointed to one of the corners of the cube. The alpha collectors would be placed in the cube's corners. In this arrangement, each alpha collector would be the same distance from the center of the polywell as in that BOE calculation, but the whole arrangement would fit inside a 3-meter cube, instead of a 5-meter sphere.

Or another possibility... since we know where the alphas are leaving the polywell, we could conceivably put one or more toroidal magnets outside each cusp, to steer the beam. If these toroidal magnets are as powerful as the ones in the polywell, they wouldn't have a problem with alphas impinging on them, either. But what this would allow is a repackaging of the reactor into a cigar-shape instead of a sphere. With an octahedral polywell, beams of alphas emerging through each of the four west-facing cusps would be magnetically bent so that they aim due west, and the four east-facing cusps would be magnetically bent so that they aim due east. The entire reactor could then be packaged inside a cylindrically-shaped vacuum chamber with the alpha collectors at the ends. The reactor might still be five or more meters long, but would be significantly narrower--enough to fit on, say, a regional airliner or a locomotive.

These are a few ideas that came to mind when I read the earlier thread. Now, I'm no physicist, and have no idea whether these ideas would work out. If they're completely unworkable, I'd love to hear someone who knows what he's talking about weigh in and explain why....

[Mike Holmes]

Huh. Dr. Nebel just posted here that the WB-7 chamber is cubical.

viewtopic.php?t=1297&start=60

Or are these ideas not related?

Mike