night I changed the SimIon model to use one electrode for the entire cage and
received much better agreement with the five fold symmetry. In the
previous model, each of the great circles was a separate electrode. I know
this was bone headed, as they are all at the same potential, but I won’t go into
the reasons why this came about. The extra bonus is that the field
calculation is about half as long. Only two electrodes, not 7. <heh>
I can be silly at times.
In any event, on the left is the field contours of the new model.
Unlike the previous model, the icosahedral symmetry is obvious… Which
makes the model a far better analysis model!
clear that a lot of the chaos I saw in the previous model was a Tiffin phantasm
of the way the equations were solved. Which is pretty good news.
On the right is the electron
trajectories resulting from injecting electrons in one of the pentagon faces.
The view is the same isometric vantage point as the
above field image. The
injection point is just inside the actual radius of the cage. The energy
of the electrons is 7.71 keV, directed along the X axis. The potential
contours are nice and smooth and regular. I believe that I’ll have to have
some directional focusing to capture the majority of the electrons, but a simple
Pierce reflector should be sufficient to focus the beam. It’s the
direction that’s hard to get accurate without deflectors.
The injection energy is 10 keV or less in the pentagon faces, and that means
the electron guns will be a lot simpler to construct. I also found that
the ideal grids that SimIon allows will give a reasonable approximation of the
virtual grid formed by the electrons. Too ideal… But it’s a good
What’s nice to have confirmed is that it doesn’t take much of a change in
momentum to push the electrons into the right contour. For example, a
difference 10’s of volts on a base of 7,000 is enough to shift the electron’s
trajectory into reverse. The addition of the magnetic array should add
just the right kicks to keep these beasts caged for a significant number of
orbits before becoming power losses.
On to the magnets.]]>
got some time and dug into simulating the beast with SimIon.
Click here to download the SimIon geometry
files. Why was this hard? Just figuring out the three
dimensional rotation matrices, that’s all. Tedious, as the SimIon
reference frame is a right handed, and the reference frame I had from my cad
system is left handed. Projection and a few sign changes later and I had
the icosidodecahedron cage modeled as an electrostatic potential array (shown on
the left). Click on the image for the
full size image. It’s the standard 3D isometric viewpoint of the
icosi-grid as modeled in SimIon.
have only modeled the electrostatics. I have yet to add the magnets to the
simulation. I must say that you can see the symmetry bias quite clearly.
First, SimIon represents 3 dimensional space via small cubes. So the
icosi-grid structure has some significant aliasing. Nothing really
horrible, but certainly noticeable. It becomes even more noticeable
when you plot the potential contours for the beast (shown
on the right). I know it’s a really complicated contour plot, but it
is using the same isometric view of the cage
The immediate thing that stands out from the field is the one great circle
that happens to lie on the Y-Z plane. This is the only great circle
that lies on the icosi-grid which aligns with the 3 ordinal planes of the cubic
system of SimIon I might add. Why am I even mentioning this? Well,
technically, all 6 great circles that make up the icosidodecahedron are the same
great circle – just in 6 different orientations. This should result in a
five fold symmetric figure – i.e. all 6 great circle’s should have identical
fields. But such is not the case because all I have to divide up the space
with is cubes. Cubes results in an aliasing of the space partition, and
thus the imposition of symmetries not in the original model.
<sigh> That’s okay. The simulation is far better than required to
do some serious engineering with, however!
BTW, the simulation took up 270 megabytes of grid memory alone! It took
SimIon to calculate the potentials for the seven electrodes (six great circles
on the icosi-grid plus the spherical chamber ground) about an hour or so on my
1.7 GHz P4 laptop. Non trivial calculation times.
Right now, the simulation is a solid ground potential spherical shell
surrounding the the icosi-cage electrode in the center of that sphere – held at
-30,000 volts potential. To make this more accurate, I’ll need to poke the
holes in the sphere that approximate the actual geometry of the vacuum chamber.
It will significantly change the field – that much is clear. So it’s
necessary. I can also try to rotate the entire icosi-cage before
calculating the fields, removing the aberration of the Y-Z great circle.
ran some electron trajectories using this set up, and they were very promising.
As I said, more than good enough to do some real engineering. On the right
is a view of one of the runs.
Click on the picture for the full size picture.
The grid and vacuum chamber are not shown in the picture, but roughly the
same orientation is used as the previous graphics on this page. The
electrons were shot into the open pentagram of the icosi-cage, sharing the
X-Axis of the model view.
What I was hoping to happen has indeed shown to work – at least in
simulation. The electrons are shot into the icosi-cage with a potential of
15,429 volts. As you can see, they actually penetrate to the center of the
cage and spin out – tracing the field
contours shown above. There was some question as to whether one could
really inject electrons into the negative potential inner grid. Since the
grid is mostly empty space, there field isn’t uniform. So only 15.5 kV is
needed to inject the electrons using an electron beam.
I found that if you inject the electrons on the same radius as the icosi-cage
– i.e. an electron emitter sitting right in the open pentagon at the same radius
of the cage, you can inject electrons with only 1.5 kV of potential.
Pretty nifty – if true. Far easier to build an electron gun that only
requires 10 keV or less. And what I think I can show with more simulations
is that I can simply use the electron gun equivalent of a flood lamp – i.e. an
unfocused electron source.
This vastly simplifies the complexity of this hair brained idea I have.
What’s also interesting from the electron trajectories I have modeled so far
is the very nice spiraling and symmetric splitting around another axis.
Obvious from looking at the field contours, and obvious in hindsight, but
pleasing to see none-the-less. I think once I add the magnetic circuit of
the icosi-cage, I’ll have a very nice electron trap. A very nice one
The magnets are going to alter the momentum of the electrons. They
don’t provide a conservative force, rather an orthogonal force via the cross
product. But the whole point of the icosi-cage is to provide an
advantageous geometry for making use of these cross-product forces. The
way that I see the electron trajectories bouncing around, the addition of
magnets should be more than enough to push the electrons into a nice bouncing
orbit around the insides of the icosi-cage.
I did a few ion simulation runs, and they were pretty fun, too. The
trajectories are much more chaotic. The focusing of the beam is much more
important. And I can’t effectively simulate the space charge of the
virtual grid of electrons… Once I get the magnets in, and assuming that
the structure actually is an effective electron trap, I can simulate some of
that in SimIon. I was thinking of using some point electrodes (pixels) to
simulate the space charge as well. Hope that works. Should provide a
In any event, it’ll be interesting to find out. Next step is to add the
magnetic circuit and see if there is the effect I believe it will.
In more real news (as opposed to simulated news), I got the electro polished
cages back. They’re absolutely gorgeous. The stresses in the cages
have also evened out nicely, so they look very symmetric – not a lot of
irregularities. Very nice. I also built the ceramic insulator
standoffs. I used the vacuum grade epoxy and constructed 9 of them.
I need 10, but I only ordered enough parts for 10 and I broke one of the
cylindrical standoffs when I was trying to drill a venting hole. Can’t
really drill fired ceramic without special equipment. As the standoffs
have screw holes, and I epoxy’d a ceramic ball on top of one of these holes
(I’ll be posting pictures later), I may have a virtual leak situation.
I’ll have to see. Hope not. The epoxy forms a tight seal…
I tried to come to grips with the wiring of the grid from the electrical feed
through. Got a little bit ugly, but I think I may have a way to do it
simply. We’ll see. I have to drill out a hole on those electro
polished pieces of beauty… Then I have to mount the insulators, then
mount the magnets. Joy of joys. The magnets are always fun to have
flying about So, still lots to do. Hopefully I’ll have more time
So I spent today fixing up the lab. Looking pretty good. Enough
light now. Put in some power strips. I spent the rest of the day
bending and spot-welding the final cage. Looking good. I’ll send it
down to Huntington to get it electropolished this week. Lord only knows
how long it’ll take to get done, but at least it will be in the pike.
Still waiting for the back ordered ceramic balls for the support standoffs.
Geez. SmallParts should have that in any day now… Yea.
I do have some good news. I ordered a copy of "High Voltage Laboratory
Technique" from AstroLogos books. They apparently have the copyright on
this book and reproduce it for a fee. It wasn’t that expensive, and this
is a classic work that I really wanted to have. Unfortunately, that was
three months ago. Seriously. I ordered this Nov 21, 2002 and it
still isn’t here. Now, granted that they have to perform blood rituals to
get this 1954 classic printed, but geez… The lesson is, NEVER ORDER
ANYTHING FOUR DAYS BEFORE THANKSGIVING. I mean, I see this all the time.
Every place I’ve worked has always scheduled a release in November-December.
Guess what? It’s non-stop holiday madness for the entire two months of
November and December. People don’t get over their new year’s hang over
until at least January 15th. So anything that has to be done during these
three months just isn’t going to get done. But humans in America still
labor under the illusion that stuff actually can get done during this time.
I’m one of the hapless fools that believe this, obviously.
But in theory, the long awaited tome will be here next week. It was
sent Thursday… Let’s hope it will show up.
Anyways, the HV cable should show up for the Bertan here pretty soon.
I’m going to have the gas line spur removed, hopefully this week. I’m
ordering some 2.75" nipples and I have some 2.75" blanks lying around. I’m
going to talk to the good folks at Heat Wave
Labs to get some dispenser cathodes so I can start playing around with some
ion and electron guns. Everybody seems to be building them these days <g>
so I should get with the program and start building some of my own hair brained
So, lot’s to do. Not much time to do it, of course. We had two
people quit at work – for good reasons. One has his fiancé in France,
another has his wife in Dallas, TX. But we’ll still miss them very much.
So, more workload for me – in addition to the extra load of interviewing
replacements. <sigh> I really, really, REALLY hate this economy.
It sucks something fierce.
In any event, I’ve been getting much better at organizing my time, despite
all this madness. Sorry to harp… I’ll get back to work
paving the path with good intentions, Brent came over and we played around with
the Spellman HV supply. That supply is a 30 kV, 2 mA supply, but still
nothing to ignore when its plugged in. I hadn’t tested it since I got it
off of EBay, so I was itching for the chance. Brent brought over his 40 kV
probe he had gotten and we figured we would ramp it up and see if the supply
worked – always a useful thing to know. So I had an old Fluke DMM and I
had also gotten 22 100 M Ohm HV resistors also off of EBay ($15 – such a deal).
So after a few trips to the hardware store and our local radio shack for some
wire and some terminal bars, we rigged up a simple test load for the supply.
Always a darn good idea to have a test load for an HV supply…
So we connected one of the resistors and cranked up the supply to 15 kV,
which is the rated voltage for these resistors. It was fun. But not
half as fun as listening to the crackle of the setup. Brent had gotten the
HV probe from EBay I think, but it didn’t actually come with the tip. So
one of the hardware trips was coming up with a screw of the correct size to
replace the tip. Well, actually, the original intent was to use the screw
to pull out (Brent theorized) the connector so he could screw in the tip he had
ordered. He had the wrong tip, so nothing we could do – short of
destroying the probe – would allow that tip to work. <heh>
So we just
used the screw as the probe. The vast pointy area of the screw threads
make a wonderful corona producing surface, but what the heck. At 25 kV we
couldn’t see any corona even in the dark – heck it was only half a mA max
anyway. Hardly anything to write home about. But we managed to crank
up the supply to most of its rated values. To the right is a picture of
the load we came up with. Nothing exciting to those seasoned veterans of
high voltage experimentation, but we were pleased any way.
I was especially pleased that Brent didn’t seriously injure himself.
Mind you, Brent is no dummy when it comes to electricity. He works with it
a lot, and is quite the safe guy. But in the first test, Brent went and
tried to put his hand near the one resistor to see if it was heating up.
Something that you’d feel perfectly safe doing at 50 volts and below. It’s
not like anything around this potential level going to arc out and bite you. After all, air is a pretty
decent insulator, and this is a DC voltage. Not some high frequency stuff
from some Tesla coil or something.
But 30 kV is a different thing entirely. It does jump out and bite you.
It was a very stupid thing to do. Brent has a lot of habits picked up
from his years of working with electricity. Some of the ones that are okay
for low voltages are really bad in the realm of high voltages. It’s just a
completely different world when you’re beyond the breakdown voltage of air.
You simply don’t have to physically come in contact with a conductor to get
We did observe something that we couldn’t adequately explain, however. If you look
at the picture above and to the right, you’ll see a green wire connecting the
two resistor bundles. When we got the voltage cranked up to 15 or 20 kV,
the green wire on the right of the terminal block started vibrating. At
first, when I mentioned this, Brent said that it was his hand shaking. I
couldn’t see any other vibration in the system, and I was looking intently.
So we shut everything down. Removed Brent from the system (i.e. no probe)
and tried the experiment again. The wire started vibrating again. So
now Brent was convinced that something unexpected was going on.
Note that this side of the resistive load was connected to the negative 30 kV
side of the supply. The system is symmetric, so the other green wire – on
the ground side – wasn’t vibrating at all. There was a metal bar under the
table. Brent thought it might have something to do with it. So we
moved the load away from it, and tried it again. Same result. Then
we turned off the lights to see if there was any corona that might help explain
it. No such luck – certainly to our eyes. And it’s pretty dark down
there with the lights turned off.
In any event, we think it’s just related to having a potential of 30 kV on
that wire. The air in the lab is pretty humidified, being so close to the
Pacific ocean. It’s not like it’s the national institute of standards down
there. Lousy grounds are still grounds, and we do have the ground return
to the supply in close proximity – so I wouldn’t be surprised if it was just
attracted to that. But we had never witnessed this effect, so it was kind
of cool to see. I’m sure it’s no mystery to HV veterans, so I’d love to
hear the real explanation – love to check my theories. Kinda cool to see.
Naturally, after we had
played around with the home made load, the real HV
test load I had snagged off of EBay for a steal showed up. The next
day. On the left you can see it in all it’s strange glory. The unit
stands about 18 inches high and is about 7 inches in diameter. The
resistors are the blue columns in the picture, and they are about 1.1 inches in
diameter. The top is aluminum, nicely curved structure – not a doughnut.
We don’t have a clue as to what potential its rated for, but the resistor
columns are 15 inches in height. So we’re guessing about 75 kV or so.
I think 30 kV, which is all I can output anyway, will be pretty safe. I
think, judging from the sheer size of the resistors, that the thing can handle a
kilowatt for short periods. I mean, the resistors are just simply massive.
In any event, I think I can use it to test the Bertan when the cable comes
sometime in the next week or two.
Oh, on Monday, the 90 kV supply showed up. Well, that was fun. It
was shipped in two packages. One contained the power control and supply
and the other the voltage multiplier. The package containing the
multiplier was soaked in oil – obviously insulation oil from the multiplier.
Hmmm. What to do? The poor UPS guys give me a choice. Accept
the shipment, or decline. Well, not knowing if this insulation oil was
hazardous, I said "decline, please", and they drove off with the packages.
The control system and main supply package was also soaked in oil, from the
runoff of the multiplier. I just wasn’t prepared to store something that
may have PCBs in it downstairs…
I once had several 7 kilo Joule capacitors (yow!) that were in my garage for several
years. They had PCB insulation, and I eventually had to get rid of them at
a toxic waste facility in the county. Not fun. Kinda terrifying to
have around. Not immediately dangerous, but something always gnawing at
the back of your mind. So I wasn’t in any mood to deal with this.
I’m still talking with the guys who sold it to me. It was insured, so the
money will all work out in the end. But I have to wonder. First,
what in the heck is UPS doing to these packages? I mean, I’m
assuming the people who sold me this supply shipped it in good faith. I
severely doubt it was leaking when they packed it. This is a company which
seems to be on the ball, and they would be just completely insane to do
something like that. So I believe it was in good shape and pretty well
But it was in a card board box, weighing in at 174 pounds. So that
wasn’t probably the best packaging scheme. Especially with fluids.
Got to have a hard container because people who ship things are pretty rough on
stuff… Likely they were moving it and BAM! It falls on the edge,
or something falls on it, or its dropped 4 feet off the back of some truck, or
falls off a conveyor belt. It likely bursts a seal or something, and then
the inevitable leak starts. God only knows how this will work out.
Definitely entertainment, though…
So I got some DB 15 connectors and some shielded 25 wire cable. I just
have to make up a connector, wire it to the lab jack, and I should have a
controller for the Bertan supply. The Spellman seems to have some remote
controls and monitors, so I should be able to drive that as well. But I
don’t have the schematic or pin outs yet from that unit… But they should
be here soon. But I’m getting the hang of LabVIEW’s programming language
and should have something measurable from the LabJack on the voltmeter and be
able to measure a supply input from a test input. That’ll be fun.
Automation is always cool. Then I’ll have to see if I can drive the
hydrogen mass flow controller. I’ve got the pin outs and signals needed
for those, and they look really straight forward. No big mystery there.
So that’ll be fun, too.
Since Brent is out of work, he’s volunteered to do some leg work for various
things that need planning and pre-positioning. That’s useful.
Hopefully he’ll lose his temporary unemployment, and he won’t have this
wonderful stretch of free time that he’s enjoying now. But until then, he
is going to be doing some useful stuff on various fronts.
In any event, I know it’s not much to report, but it was the best I could eek
out this weekend. Nothing too exciting, but fun none-the-less.