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Re: Terry's New Plane Wave Antenna



Original poster: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>

Stork wrote:

> Let us not forget though that the electric field from
> the TC is alternating between negative and positive charge

Sure, but (we presume) the electrometer is responding to
an additional (non-oscillating) field from bunches of
ions left hanging after the bang.  The TC topload and
coil winding will have zero charge after the event
(maybe not so the coil surface), so any residual electrometer
reading is attributed to the space charge - if the
instrument is working!

> from my direct observation of Richard's experiments and
> from conversations with him, he finally deduced that there
> is inborn error in the Keithly 610C electrometer design.

Well that's a good bit of info.  You were there?  What
electrode was used, and how far from the TC?   From that
we can estimate the peak potential of the 610C input,
and see if it exceeds 100V.   If it does, and grid or gate
current flows as a result, the device will report a residual
charge of opposite sign to that which caused the overload.

> by eletrostatic induction the normally neutral probe will
> obtain a negative charge from a negative space charge.

A positive (say) source charge induces a negative charge on
a test probe and (by charge conservation) a positive charge
on the input of the electrometer.  Having thought about it,
I don't think there's any ambiguity here - the instrument
would read + in this case.    If the charge was collected
by the probe (rather than just induced), the probe would be
positive and the electrometer input would (this time) also be
positive again.

Terry wrote:
> Sounds like we might need some new experiments to resolve
> that since the old and present data is a little too messy
> to go from...  I would not be surprised to find that coils
> can charge either negative or positive depending an many
> things....

I agree with all that.  Also, we know that if the coil base
terminal is grounded via a DC blocking capacitor, there will
be some residual voltage across that cap.  If space charge is
being generated, for total charge conservation, the space
charge should be equal and opposite to that left stored on the
blocking C, should it not?   As Dmitry mentioned, other things
will collect charge too, and also have charges induced.  The
electrometer can only respond to the total field, so an
electrically 'simple' enviroment would be nice for these kind
of experiments.

> I thought this was all figured out in the past, but it
> appears that it is not at all...

I don't think we (here) know much about this.  I'm sure there's
much in the literature, but sometimes it's nice to measure
these things ourselves, and see that they work.

Some of the things I'm not clear about are
a) What's the nature of the space charge, is it always one
polarity or the other?
b) After the bang, the grounded coil has no charge, therefore
for overall charge conservation, there should be some opposite
charge lying around somewhere. I mean, if the bang goes off inside
a Faraday cage, and (say) there's a bunch of positive ions left
hanging in the air, where has the negative charge gone?
c) How fast does this static charge distribution decay?
d) Does it affect the next bang?  Does anything 'build up' over
a series of bangs?
--
Paul Nicholson
--