R
Robert Baer
I do not think that inductance is the issue / problem source.Hi, thanks for all the feedback.
This thing is getting curioser and curioser.
There does seem to be some interesting things going on in the tube. I
never really gave much thought to how complex the process might be.
Thinking of the current in terms of electrons flying one way and
possibly xenon ions flying the other way with all the associated
momentum, KE and stuff seems to have some potential for odd things
happening. I mean like Clifford said somehow they have to stop at some
time after the voltage is removed. What the implications of that are
way beyond my knowledge of plasma physics, which is more or less on
par with what my cat knows. Is there enough momentum in there to have
any significant effect on the current voltage characteristics and is
it even relevant - I really don't know, maybe it is far too small to
be significant or maybe not. Also, in some other tests I had done
some time ago I was looking at how the light output decays at turnoff
and found that the light output only starts falling a few microseconds
after the turnoff and takes quite a while (several uS) to fall
appreciably, so I supose there is still quite a lot of chaos going on
inside the tube even after the supply voltage is removed. It seems
very plausible to me that all those hot ions and electrons would not
just let the tube terminals float peacfully to zero volts. However
that supposition could be simply based on my lack of knowledge of how
such stuff works rather than anything else.
As Tim said there is also the possibility it could be plain and simple
inductance at play though I do have my doubts since my load resistor
was placed right instead of the tube leaving all the wiring just as it
was. That leaves only the inductance of the tube itself being
different between the two cases. Also, I have made a simple
calculation on what an inductance of 0.1uH would need if made by
winding a toroid. It resulting (if I calculated right that is) that a
typical way of achieving that would be a toroid with 5 turns on a
100mm (4 inch) diameter air core. That is about 60 cm (2 feet) worth
of wire, a lot more than I have between the various parts of the high
energy circuit. I have also tried as much as possible to have all
cabling in such a way that they are always in antiparallel, so for
instance the pair of wires going to the tube are kept parallel to
eachother all the way to the tube and so on, hoping that that will
cancel out some of the effect of the inductance.
What I shall be trying to do to find out whether or not it is a matter
of tube inductance is to construct a 0.7 ohm resistor which will have
a shape very similar to the tube. This I will make out of a good
number of 1 ohm 1/4 watt resistors trying to mimic as much as possible
the shape of the tube. The tube is a U-shape with each leg about 140mm
long and a tube diameter of some 10mm. I will stick this weird right
instead of the tube and see what happens. Hopefully the resistor will
last long enough to allow me some meaningful measurements.
I'll also be making that current transformer to get some hopefully
more accurate current measurements. The differential voltage probe
however is something that I haven't yet figured out. I checked on
eBay and the cheapest ones cost a fortune so I'll have to bodge
something together myself.
Without very special precautions (gas pressure, current range, aging,
addition of radioactivity, and i do not know what else), gas in a tube
will have regions of negative resistance; in the right conditions, one
can see a "crawling worm" of plasma in a gas tube.
If you want to get "precise" data, then use a current-limited supply
set to (say) 50V (no less than 32V) and slowly adjust that limit from
(say) 1mA ("engineering zero") to the max of the supply, while
monitoring the tube voltage and current with a scope.
Use a trigger transformer to start the ionization.