Re: Any Very High Freq. TCs?

To: tesla-at-pupman-dot-com
Subject: Re: Any Very High Freq. TCs?
From: Richard Hull <rhull-at-richmond.infi-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Thu, 03 Sep 1998 22:03:42 -0600
Approved: terryf-at-verinet-dot-com

Tesla List wrote:

> Original Poster: Julian Green <julian-at-kbss.bt.co.uk>
>
> > Original Poster: Steven Ivy <adder_black_the-at-yahoo-dot-com>
> >
> snip...
> > volts at 1 GHz operating on my kitchen table : ) Is there some
> > particular flaw in this scaling idea other than the difficulty in
> > producing a spark gap capable of operating at these very high
> > frequencys.
>
> Have you wondered why you get streamers that terminate in thin air?
>
> Well I believe that it is due to the capacitance of the air
> and its ability to ionize forming conductive clouds of gas around
> the coil.
>
> The current in a capacitor rises as the frequency increases.
> Therefore as the frequency of your tesla coil rises so does
> the ability of the surrounding air to disipate the high voltage.
>
> The result is that as frequency rises the streamers shorten. At
> about 1MHz you get discharges that look like a gas cooker flame
> and loads of ozone.  I think Richard Hull has photos if this.
>
> If you want long and impressive streamers go for low frequency,
> around 100KHz.
>
> How many turns on the secondary would you need for a 1GHz tesla
> coil?
>
> Julian Green

Julian and Malcolm echo my sentiments.  Both the capacitance and
inductance of an HF coil would be so tiny that real resonant rise into
the MV range just could not occur in air.  Such a power density would
corona and bristle with losses.

The CEBAF <continuous electron beam acceleration facility> accelerator
here in Virginia (most powerful continuous electron accelerator in the
world) uses super conducting pure niobium resonant cavities and develops
6 MEV rise across the waveguide cavity's throat which is ~1" across with
no arcing.  There are a gang of these cavities in series. along the
large race track.  The frequency is in the Ghz range, but there is, alas
no, spark.  It is slightly inhibited due to the entire device being
under one of the hardest vacuums known to man >10E-10 torr.  This is all
I can learn.  They are reluctant to release great detail on the ultimate
vacuum and certain aspects of the liquid helium distribution network.

The head of engineering at CEBAF and designer of the cavities comes to
our TCBOR meetings once or twice a year.

Richard Hull, TCBOR