From:
"Mike" <induction@comcast.net>
References:
<bu3j52$8d7r$1@saturn.cs.uml.edu>
Subject: Re: DC plasma
discharges
Date: Fri, 12 Mar 2004 20:21:21 -0500
Newsgroups:
sci.physics.plasma
Hello! It's a bit late to start a reply, I
have to work in the morning, but
here goes. Have you tried making sure the
power supply to the filament is
isolated from the main power supply
driving the (main) plasma?There should
be no common connection but the
signs point to it; One electrode is pairing
off with one filament terminal
by what you report.
Distance may
not solve your issue, after work I come to our lab and work
with large
glow discharge tubes, the largest is 6 feet tall, 2 feet wide, 3
pumps,
not much waiting. The ID is 22.5 inches, 3/4 wall Plexiglas.
When you seek isolation, be sure that the
stand off voltage is much
greater than the DC supply to the earth ground
else it will try and break
the windings down because the filament
transformer primary will be off the
grounded power line.
We run the base and table of this discharge
tube earth grounded so that
the meters interfaced to computers are
protected as are the operators.In
addition to the common connection you
seem to have in the power supplies, it
sounds like the filament is
sputtering off material. Actually, it sounds a
bit like one of Langmuir's
studies. He started a plasma, heated a filament
then turned the filament
off quickly, then back on. The current spike, as
the filament was part of
the circuit, sputtered off material and that lasted
a long time in an
unusual "liquid" acting display.
Regarding the distance issue, once it's fired, I can run the
current from
10 amps and lower it all the way to 400 Microamps before the
tube will go
out at ~60 MiliTorr and that is with the electrodes 6 feet
apart.
We are using this tube in
a study to determine how much light , N2 first
positive, air, results from
how much power per unit volume related to
obtaining a calibration curve
for Sprites. Our PI gave a talk at the January
5th, 2004 URSI meeting in
Boulder with our current results. The power point
file and .AVI movies are
available.
You should get
spectra on what you have for the display, then you will
have a better
idea. We use the large tube for other projects and in one run,
I had two
independent power supplies going of opposite polarity. We can do
~2600
volts at 10 amps DC, very well filtered. I was able to bias the plasma
with
isolated electrodes at different locations and the Ion wars were most
impressive!
Going to higher pressures will only make it "Snake" and be
constricted.
Are you getting striations in the undesired
glow? Besides the hot
filament helping the discharge, In the end I think
your filament power
supply must be isolated from a common point and the
problem may reduce if
not go away.
Hope this helps and let me know,
Mike
"McMendes"
<jcm310@hotmail.com> wrote in message
news:bu3j52$8d7r$1@saturn.cs.uml.edu...
>
>
Hello everyone!
>
> I'm using a DC plasma reactor. I create a H2+CH4
plasma when I apply a
300V
> DC voltage. Very stable. Then I start
applying a DC voltage to a filament
> and I get glow discharges between
one of the filament electrodes and one
of
> the plates used to
ionise the plasma.
>
> I don't get it. When I create the
plasma, that means I ionise it. So why
do
> I have new ionisations
when I have the discharges? Are new species
ionised?
> And how can
I help it? I've tried using higher pressures (to make the
plasma
>
"smaller") but then it gets denser and more conductive; I've also
tried to
> increase the distance between the filament and the plate.
Anymore
> suggestions?
>
> Any help will be very
welcome. Thanks!
>
>
>
>
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