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Mr. Fusion
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Multipacting Patents
October 11, 2002 — 16:44


God,
I simply love patents.  Kudos to the theory that we can grant short term
monopolies for publishing of the information.

I went searching on Delphion for some
patents on ion guns and found a nice and simple
design (fig. 1 on the left).  What’s
funny is that this is just a cylindrical version of the fusor adapted for ion
generation.  The previous ion gun patents by Farnsworth and Meeks were
assigned to these guys, so it was a nice coincidence to pick up the patent while
trawling for ideas.


As
you can see from the cross section shown on the
right, the system uses
the multipactor grid design to bombard the gas with electrons and then
accelerate the resulting ions out of the gun.  Nice and simple design that
someone like me can perhaps make.  We’ll see.

I used a different mounting mechanism for milling the .25" bars for the
chamber cage.  I had this small tilt table from Smithy that provided way
superior clamping and alignment.  It’s still sucks a bit because it takes
more time than it should to clamp a piece.  And because the table isn’t
very long (8"?), you can only mill out a section less than 6 inches – the clamps
prevent milling the entire length.  But it’s faster than the sad mechanism
that I was using before because the bar is positively clamped flat against the
table.  I got four bars milled which gives me about 12-16 half edges. 
For the octahedral cage, I need 48 pieces – 2 for each of the 24 edges of the
octahedron.  So it’s going to seem like forever to mill these all out.

Again, it’s clear that I’ll have to build a specialized chamber just from a
logistics point of view.  The mountings would be much more stable and the
number of feed throughs and such required becomes much smaller.  But
there’s a lot of design work and testing I need to do way before then, and my
current chamber will work just fine for these activities.

I talked to Harlan about the symmetry of the standing waves I was wondering
out loud about.  We came to the conclusion that it was indeed impossible to
subdivide the surface of a sphere with only hexagons.  You must indeed have
at least 12 pentagons mixed in among the hexagons.  I’ll post the proof
when I find it on the net (or in a book).  But I’m now confident that this
is indeed the case.  We also agreed that the magnetic fields (and
electrostatic, in the case of electrode only IEC) would be a strong determiner
of the standing wave symmetry.  We both thought that it would take an awful
lot of work to not produce standing waves that aren’t aligned with the
symmetries of the surrounding magnetic and electrostatic fields.

Whether the ramifications are trivial and have no impact on ICC, or whether
the strategic control of the ion acoustic wave symmetries has a measurably
useful effect remains to be seen.  However, it seems plausible at the
moment to my addled brain.


One
thing that is very interesting is to use the models I learned from Buckminster
Fuller for

creating spherical polyhedra from the folding of great circles
as models of
the ion standing waves .  Figure 831.31 shows
six cases of symmetric folding of circles. 
Figure
458.12
shows two folding patterns which produce five fold symmetry (shown on
the right).

It will be interesting to get to the point where I can actually do some
rudimentary experiments regarding the role of symmetry in the production of ion
acoustic standing waves.  For now I can only theorize and perform thought
experiments while I mill out the bars and build the first cage.

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