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Mr. Fusion
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And so it begins
September 25, 2002 — 4:17


I
got the vacuum system today.  I picked up the cargo van from the Enterprise
rental place here in HMB around 8:00.  I was remarkably calm.  I only
actually started dancing around like an excited puppy when I actually saw the
system pumped down to 10-6 torr at
Duniway.  The little midget was
humming silently along like a dream.  We lifted it into the van and I was
on my way home.  It was pretty surreal, as beside me in the passenger seat
was the 12"x18" Aluminum bell jar.  Strapped in with the safety belt,
bobbing up and down in the nicely padded seat.  Like the seat belt would
hold the mass if I decelerated quickly.  Oh well.  I had a bitchin’
vacuum system, so a few risks are warranted (tee hee).  Besides, I actually drove the
speed limit the entire way in the right lane.  It’s refreshing to remember
the experience.


The
system is a rebuilt Leybold TOPS 151.  It’s a very nicely built, compact
turbo pumping system with a pretty large capacity.  Oil free.  :) 
I opted for an upgrade to the 361 turbo pump.  It’s rated at 345 liters/second, with
ceramic bearings.  Air cooled.  Yum.  I’m pretty sure that the
backing pump is undersized for this  for the system, but I’m not
complaining.  10-6 after 3 hour pump
down on a non baked system – one that’s had the aluminum chamber anodized just a
day before, mind you. 
And one of the ports of the bell jar was covered with a fairly ratty piece of
Plexiglas to boot.  Finally, no vacuum grease on the bottom of the bell jar
seal.  I figure if I take reasonably care I’ll be able to be in serious
vacuum pretty quickly.  The original specs for the TOPS 361 claim a pump
down time of 3 minutes for a 25 liter chamber to 10-5.
Bitchin’.

The bell jar is truly huge, with a nice big rectangular Plexiglas port down
the front.  It’s like a zillion cubic liters, but it’s truly lovely to
behold.  Tomorrow I have to stop by Tap Plastics pick up an inch thick
Plexiglas disk for the open port on the bell.  Larry (the fine gentleman
who put this system together) gave me a steel blank I can face and drill, but
I’m much to impatient for that.  Besides, if this system got to 10-6
with a ratty piece of plastic, it’ll be handy to have a nice big access hole I
can just cover with a piece of plastic.

Mental note: install a ceiling hoist so the bell jar is easy to lift.

I also got the magnets from
allmagnets.com
.  These are
big honkers – 4.5" OD. 
Grade 5 ceramic, 3800
Gauss
Tasty.  My poor wife didn’t realize
what they were and accepted the package and luckily left it downstairs because
it was fairly heavy.  Heavy means it belongs in the workshop.  So
luckily these 20 magnets didn’t end up anywhere near sensitive magnetic hard
drives.  Mental note.  Do not bring extremely powerful magnets
anywhere near electronic equipment.

These magnets are very cool.  Magnetism has always been one of the most
visceral of the fundamental forces for me.  You can definitely feel the
fluidic nature of the force as you play with magnets.  20 of these suckers
in serial is pretty powerful and you can really feel the fields interplay. 
I can really see the allure of
magnetohydrodynamics.


The system I’m going to play with is ridiculously simple.  Some amateur
fusion experimenters have had some truly
spectacular
successes
with
Inertial Electrostatic Confinement
(IEC) using spherical octagon grids. 
These systems are incredibly cool and surprisingly low tech.  Playing with
25 KeV is non trivial, though and I’m constantly reminding myself of the dangers
of high voltage and other nasty stuff.  But I think they have reached the
limits of electrostatic confinement.  I’ve gotten a hold of Bussard’s
patents, and have been generally digging into current thinking in plasma
physics.


In
patent number
4,826,646
, Bussard describes an elegant device for overcoming the
limitations in devices based on the Fansworth, Hirsch
and Meeks
design class.  The basic problem with using grids is that you
can’t make the grid cross sectional area small enough.  At least that’s the
way it seems.  I’m not really sure because Bussard’s other patent, number
5,160,695
has a number of grid based confinement systems diagramed.  I particularly
enjoyed the spherical tetrahedral grid.  Very pleasing to my Synergetic
sensibilities.

So anyways, Bussard’s very clever idea is to create a magnetic bottle for
containing the electrons.  Unlike other controlled fusion devices which use
magnetic fields to contain the plasma, IEC uses electrostatic forces to create
the ion densities necessary for fusion.  In Bussard’s design, a polyhedral
magnetic bottle is constructed to constrain electrons at the center of the
sphere.  These electrons are injected via the faces of the polyhedron into
the center.  Eventually you can build up quite a charge as these polyhedral
magnetic bubbles are quite efficient at keeping the electrons you inject inside
the system, squeezed down in the center of the device. 


Arranging
the magnets strategically in a polyhedral array has the effect of creating a
magnetic trap that only has point cusps (figure 1c on the diagram to the left). 
This means that only electrons traveling in trajectory within a narrow solid
angle can escape the system.  If you balance the electron’s energy with the
strength of the magnetic field you have very low losses within the system.

The very first thing I want to do to shake out the system is to simply inject
some low energy electrons into the system – say 50 electron volts. Keep the
pressure just below 10-2 and see if I can get a
glow discharge from the residual air.  I plan on getting a small bottle of
neon or argon so I can get a really nice glow out of the system to make some
pretty pictures.  I can use this to shake out the gas back filling
subsystem I’ll eventually need to put together.

I figure I can do a lot of experimentation with fairly
low voltage and shake out my lab procedures and safety protocols.  I
remember working with high voltage in my youth.  I vividly remember the
smell of my burning skin when I caught an arc from a 12 kV TV fly back circuit on the
back of my right hand.  Luckily I was obeying grounding procedure and I just
ended up with a really nasty surface burn.  No scarring.  It’s been a while since I’ve
done such nutty stuff so sticking with the low end of the voltage and current
scale for a while is only prudent.

I went to Triangle Machine surplus in San Jose yesterday
and saw some huge high current power supplies.  The power output wasn’t a
simple screw terminal.  It was a big, thick plated bar. 8" x 0.5" x 1.0" –
massive.  Truly
terrifying to think about 200 amps being pumped out of these surplus beasts. 
Even scarier was looking at the 30 kV, high current power supply they had
sitting out in the yard.  This thing had meters up to 600 milliamps at this
voltage.

Truly terrifying to behold.


So
anyways, the plan is to now start building the
magnetic trap
.  The design on the right is pretty simple. 
Underlying the system is a cage made of 0.25"
square steel.  I chose the
dodecahedron
specifically because of all the polyhedra Bussard mentioned, this is the only
one with five axis of symmetry.  I’ll be saying why I think this is
significant later, but let’s just say that from my
Synergetics
studies, one thing that has been driven home is the importance of 5 fold
symmetry


The
12 pentagons are also nearly circular, which means that I can approximate the
system with circular ring magnets very nicely.  I don’t want to mess with
the currents necessary to produce the field strength to be interesting. 
Permanent magnets are simple and relatively safe.  One major downside
however, is that the ring magnets I’m using have a pretty large cross section. 
They take up a pretty large percentage of the surface area of the containment
sphere.  The upshot of this is that any fusion products are going to smack
these surfaces around with some pretty high energy.  I’m not really sure
how these ceramic magnets are going to hold up under this maelstrom.  They
have an operating temperature upper bound of about 300 degrees Celsius. 
Not spectacular.  But not shabby either.  Again, I figure I can still
do a lot of useful experiments and check out some pet theories without actually
doing actual fusion and blasting these magnets with 4 megavolt particle storms. 
But then again, these magnets are cheap and can easily be replaced.

Anyways, I’ll cross that bridge when I come to it.

One of the things I was concerned about in choosing the dodecahedron as the
polyhedron was what the magnetic symmetry would work out.  I naturally have
built a model out of the incredibly useful
Zome
modeling pieces, and found that there are several interesting
configurations to explore.  One particularly interesting configuration
doesn’t use oppositely polarized faces.  It’s an elegantly polarized
system, but may turn out to be completely useless.  I’m pretty new at this
plasma physics stuff and I’ll just have to find out. 

Part
of what I want to experiment with is my notions about using a magnetic
confinement system based on the
disdyakis
triacontahedron
.  This is a fascinating structure.  There are 120
triangular faces, divided into 60 positive spherical triangles and 60 negative
spherical triangles.  Here I’m using the words positive and
negative
in the sense that a left glove is the "negative" of a right handed
glove – i.e. left/right symmetry.  Anyways, this is a highly symmetric grid
structure.

My first idea, when I read about IEC fusion was that I could use a grid based
on this solid as the anode.  My feeling was that this was the most
symmetrical grid I could imagine.  But the more I found in my digging into
IEC, the more I realized that this grid is not very transparent.  I created
an AutoCAD Inventor model of a grid and created a 1.5" prototype.  I
uploaded the STL file to some wonderful people at
SharedReplicators.com.  Five
days later a FedEx box showed up on my doorstep with a plastic model of my hair
brained scheme.

It was a truly surreal experience.

So about the time I got the prototype of the disdaikis triacontahedron grid
back from the surreal web replicators, I found Bussard’s patents and had started
reading them.  I had suspected from some writings by the fusion researchers
at the
University of Wisconsin
  that using a grid was not going to work in the
long run.  They had mentioned something they referred to as

Polywell
tm, which turned out to be
what they use to refer to Bussard’s ingenious polyhedral magnetic trap. 
All of their reports and investigations seemed to point to the conclusion that
the inner grid in an IEC device had to disappear in order for the system not to
leak power like a sieve.

But I still can’t get this beautiful solid out of my thinking.  My
theory is that one can use the 15 great circles that form the basis of the
disdaikis triacontahedron as a system of magnetic confinement of electrons. 
In Bussard’s designs, the faces of the polyhedra are magnets, the current being
carried in the edges of the polyhedra.  However, Bussard doesn’t ever
mention using great circle transits as the magnetic fields, rather he describes
systems where the magnetic circuits are not formed by great circles of a sphere. 
My theory is that the 15 great circles of the icosahedron can trap the electrons
in the same manner as a balloon, by the way charged particles would bounce
around inside as system composed of these fifteen magnetic fields.

Again, only experimentation will tell me if I’m a lunatic or have found
another novel way to magnetically confine electrons.  I really think there
may be something here.  In any event, this fascination with five fold
symmetrical magnetic trap structure is what led me to use the dodecahedron in my
containment system design.

Well, that’s it for tonight.  Let’s hope that Tap Plastics has inch
thick Plexiglas they can cut for me and I can start test pumping the system
tomorrow night.

<heh>

Comments:
  • ali

    hi,i hpe you be successful in your educational ways.

    August 3, 2004 — 5:31
  • Mr. Generic

    You need round edged magnets and gaps at the vertex.

    November 19, 2006 — 22:42
  • Yea, I saw Bussard’s video, too.

    November 20, 2006 — 7:42
  • James Baugh

    The Triacontahedron won’t work with great-circle currents. Note that each vertex must have an odd multiple of two count of edges for the current to flow the same direction through opposite edges.
    The triacontahedron has several 4-edged vertexes. One opposite pair must flow toward the vertex and one opposite pair must flow away for the magnetic polarities to alternate. Otherwise you get a wire running across the center of a magnetic pane and it will be subject to the electron/ion streams.
    You’ll have to let the current turn at a right angle at each multiple of four edged vertex.

    July 4, 2007 — 13:52
  • Yea, that’s an issue, but permanent magnets would take care of it (assuming, of course, that they hold up under the heat). But I’m not going with the Triacontahedron, rather, I’ve used the Icosadodecahedron. Note that each butterfly is a great circle which folds up into the butterfly like a dream. Actually, now that I think of it, the Triacontahedron is composed of 30 great circles and is constructed using the same techniques.
    Remember, there’s more than one way to produce great circles. ;)

    July 11, 2007 — 1:00
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