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Mr. Fusion
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Plasma Diagnostics
January 10, 2003 — 17:18

Well, I’m feeling much better about things.  Usually a warning sign to
small furry animals who might be innocently underfoot.  Garret Young asked
a while ago on the fusor BBS "where’s the science".  This got me worrying
more about things that I had already worried about a lot.  Science is
asking questions, forming theories, making predictions, constructing and
performing experiments, gathering data, analyzing the results and comparing
results with predictions.

Plasma diagnostics is a pretty interesting area.  The work horse is the

Langmuir Probe
.  Since this device requires a physical conductor
actually inside the plasma, this can get rather interesting as the plasma is
easily at 25 KeV, which works out to an effective temperature of 206 million
degrees Kelvin.  But you can vary the potential in the probe, and the
current in the probe is kept to a minimum.   But this means that you
need to supply potential to the probe, and that means a very high voltage power
feed through if you think your plasma is at 100 KeV.

But diagnostics of the plasma is essential for understanding the structure. 
And if you’re experimenting on changing the structure of the plasma, you have to
find some way of measuring what you’re predicting will happen.  Currently,
the amateur work has centered around neutron measurements.  So there’s a
lot of good ideas and general engineering knowledge available in that area.

A

paper
pointed out by Garrett Young claims actual measurement of a double
potential well formed in the IEC focus.  The inner potential well profile
was measured to have a dip of approximately 200 V.  The cathode voltage for
this measurement was -7.5 KV, cathode current was regulated at 30 – 40 mA, He
pressure was at 20-30 mTorr.  This measurement was made with an amazingly
cool LIF measurement apparatus.  What they did was measure the laser
induced florescence at 667.8 nm wavelength and then deduce the potential in the
core.  Very, very cool system, and as Garrett says, expen$ive.

The cool thing is that they seem to have actually verified a multiple potential well
structure in the plasma core.

My

post
on

sci.plasma
finally showed up.  Boy does that list have a lag time. 
But it’s moderated, so I can’t complain.  Did get one answer from a Scott
Stephens.  He seems to be doing some cool stuff as well, and lamented about
the lack of anything of interest to find on the web regarding IEC in this area
(i.e. Bussard’s ICC effect).

Garrett Young suggested that I look into the research going on with respect
to standing waves in the sun after I lamented about the dearth of information on
Bussard’s standing waves on the fusor forum.  I must have had a sip too
much of wine that night and I railed on about the lack of support for five fold
symmetry in current modeling and simulation tools.  Must have sounded like
a wacko, and I suppose I am in fact one…  Oh well.

I am pretty convinced though, that the standing waves Bussard describes are
not waves generated by spherical harmonics.

As an experiment, I went and tried the
Google Answers service. 
Basically, I re-used my question I asked on the sci.plasma and sci.fusion
newsgroups.  You can see the current progress and eventual result
here
The entire process has been very interesting.  The researcher pulled up a
number of interesting sites, papers, etc that I had not been able to find in my
scouring of the net.

Part of what I’m doing here is a big experiment with the net.  I’m
trying to test the limits of this amazing web of knowledge and human interaction
to see what it can do.  I’m ignorant about plasma physics and it’s been
quite some time since I’ve been in a physics lab.  So this is all like
starting over again in school for me.  That means I make a lot of "green
horn" mistakes, come up with completely bogus ideas and have to regurgitate a
lot before I can keep some ideas down.  This web log is just a record of
what I’m doing – the good, the bad and the extremely stupid.

Speaking of stupid, on the
fusor.net
forum, we were discussing losses in the IEC fusor.  I was trying to
understand how the glowing discharge channels, so prominent in the IEC process
(i.e. the star-mode discharge) was such a huge source of losses in the system. 
I was

arguing
that the ions would maybe make it out of the electrostatic cusps
formed by the grid, but would in all likely hood reenter the system, rather than
hit the chamber walls and become neutralized.  Richard Hull wrote in his

reply
that the electron loss in the fusor was the single biggest loss
in the system.  I think he was pretty frustrated with me, as he seemed to
be raising his voice in the posting… 

<sigh>  I had forgotten that the vast majority of fusors operate in the
so-called glow discharge mode, where the grids themselves ionize the deuterium
gas and accelerate the ions towards the center of the structure.  
This results in a shit-load of electrons in the system and the system simply
leaks like a sieve as far as the electrons are concerned.  D’oh!  Oh
well, I’m not trying to show how smart I am with all this stuff…  I’m
just a rank amateur, after all, so that’s like trying to prove a negative. 
There are some really smart people out there, and I don’t learn unless I
actually ask stupid questions, or have my silly assumptions pointed out for what
they are.  <heh>  I do learn, though.  Perhaps too slowly, but
what the heck.

In any event, it’s clear why Bussard’s suggests suppressor grids in his

second patent
.  It’s to keep this massive loss of power due to
electrons to a minimal level.  But then again, that’s why the magnetic
confinement scheme of his
first patent
is so fascinating to me.  The magnetic field configuration does a great
job of keeping the electrons where you want them, instead of just heating the
fusor chamber through the power loss.

Just got the book

Principles of Plasma Diagnostics
by I. H. Hutchinson.  Man, is this a
terrific book.  It’s the second edition, and it is simply chock full of
plasma diagnostic technique and theory.  Wow.  Going to take me
several years to figure it all out, but what the heck.  What else am I
going to spend my time on.  :)

I obtained a Bertan 30KV 33 mA power supply yesterday reasonably cheap. 
Has remote control and is in very good shape.  I need to get a rack for
this.  I also cleaned out the workshop.  My wife has a tendency to
dump just about everything down there, and it had built up to a density that was
getting dangerous.  So we cleaned it out and hauled out to good will a lot
of stuff.  Amazing.  I’m rearranging the corner where I’m setting up
and it’s going fine.

Oh.  At the last minute, I called Huntington and begged them to change
my port specifications on the vacuum chamber.  The mini ports were just too
small, and the 2.75" port I had allocated for the high voltage feed through was
just too tiny.  Luckily, I had just contacted them as they were putting the
chamber on the machines to start drilling the holes.  Ye gods, am I lucky
or what?  So I’ve updated the chamber picture, which shows the ports
upgraded to 2.75", and the electrical feed through port upgraded to a 6" port. 
That size will accommodate a 100KV power feed through with no problem.  Not
that I’m going to get anywhere near that much voltage in the near future… 
But it’s a heck of a retrofit to the chamber once it’s completed.  I’ll be
posting the updated chamber Inventor files shortly.

I also had a minor heart attack when I remembered that Alumina has a
dielectric strength of only 230 Volts/mil.  Supports for my chamber would
then only handle a potential of around 15 KV.  Wimpy.  It’s weird,
though.  Some other sources
on the web show a dielectric strength of Alumina of 20 KV / mm.  I guess I
don’t understand the "mil" unit.  Have to investigate.  In any event
fused quartz rods should easily insulate the cage from the chamber. 
Looking up the definition of "mil" on the web, I find that this is a
"thousandth".  So this is an exceedingly strange unit.  This must
refer to a 1,000 of a centimeter, or a hundredth of a millimeter, if the 230
V/mil <-> 23 KV /mm relationship is to hold.  God, I simply love unit
madness.  <heh>

Comments:
  • Andrew Witte

    1 mil = 1/1000 inch = .0254 mm

    October 13, 2003 — 18:35
  • ash

    Plasma is my field Iwant to work on the topic and this is very useful invention

    January 1, 2004 — 22:20
  • kadhim

    dear Dr
    please help my sent any subject about principle of plasma diagnostic
    with bestregard

    July 14, 2008 — 13:26
  • Leave a Reply to ash Cancel reply

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