Re: TC Electrostatics (fwd)

Ed Harris wrote:
> > Date: Fri, 06 Dec 1996 22:39:21 -0800
> > From: lod-at-pacbell-dot-net
> > To: tesla-at-pupman-dot-com
> > Subject: Re: TC Electrostatics (fwd)
> >
> >
> > Your theory of the DC component of the highly damped output waveform
> > charging the test plate is an intriguing one, but I can't see how the 
> > output waveform can have a net long-term polarity (seconds), given that 
> > the primary ckt is driven by a AC source, and therefore operates in each
> > polarity mode half of the time.
> >
> >
> Rectification in gases is seen when there is a significant geometric
> difference between the terminals of the "diode". The degree of
> rectification
> is also affected by the type of gas in question. In fact, this property is
> used
> in the "self-biased" reacive ion etchers used in the manufacture
> of intergrated circuits. These etchers generally operate in the glow or
> abnormal glow discharge regions. I even built one myself back at OSU for
> etching niobuim metal films. With 20W of 13.56 MHz into the "driven"
> electrode, I would get about 400 volts DC generated across the discharge.
> This property is essential to the etching process since it rams the
> chemically reactice ions into the film to be etched. Anyway, in the case
> of the tesla coil, I would imagine ( Richard?) that the rectification would
> be more effective (per watt expended) when the coil is producing lots of
> corona and not so many arcs to ground.


The rectification effect in gases might explain some of the charging phenomena,
but I'm uncertain as to why tube-type (CW) coils don't also produce the same
rectified output effect.  Two possible explanations:

  a)  The output voltage is much less in CW coils due to the high duty cycle.
  b)  A highly damped output waveform is required to produce the DC component.

Also, if the DC component is produced by rectification of the output, then I
wonder how the plastic pieces of the secondary coilform get charged up, as they
are only exposed to the AC voltages on the secondary, before the rectification.
I guess that there could be 'micro-rectification points' on the plastic surface,
where sharp edges and imperfections produce field emissions into the plastic.

Perhaps I'll learn something in January, when I'm able to run the coil again.
I'll try and see whether flipping the primary phasing changes the polarity of
the charge induced on a test plate.