dc drive forT-coil and S-gap replacement?

From:  Greg Leyh [SMTP:lod-at-pacbell-dot-net]
Sent:  Friday, January 23, 1998 6:32 AM
To:  Tesla List
Subject:  Re: dc drive forT-coil and S-gap replacement?

bmack wrote:

> >" Primary switch - Modified GTO
> >    - no moving parts
> >    - higher efficiency
> >    - ultimate quenching capability
> >    - much lower primary impedance(and therefore voltage) possible
> >
> > The coil itself would have a coupling between 0.25 and 0.35,
> > given the quenching ability of the GTO stack.  Any energy that
> > was not absorbed by the arc would be actively switched back
> > from the secondary into the primary capacitor bank, thus reducing
> > considerably the actual demand from the prime power source.  The
> > power factor would be around 0.98, due to the linear charging
> > ramp on the pri cap bank."
> >
> > -GL
> >
> Greg,
> Have you actually tried the this proposed circuit?  Your monster coil runs
> at 38KHZ but you're using a rotory gap.
> So far as I know, thyristers are great at switching  low frequency heavy
> loads,  but have slow recovery times.  Even 38khz is too fast for these
> devices- am I missing something?

I came _very close_ to going the GTO route, but given the number 
of untested ideas (such as pri on the inside) that I had already 
incorporated into the design, I didn't feel that I had enough time
for developing the pulse-forming networks and gate drive circuitry
for the GTO stacks.  Besides, the prices for MGTO's are starting to
come down a little, now that the development costs have been 
amortized by the good folks at CERN, and others.

The GTO's would have worked well for this coil, as the di/dt(max)
in the primary is less than 700V/uS.  The di/dt rating is more
directly the limiting factor, rather than frequency.  And as the 
coil size becomes even larger, solid state switching becomes
ever so more the practical choice over a rotary gap.

Given the mechanical and dynamic problems I've encountered 
with balancing a large 4-rotor system, I believe that this is 
the last rotary gap that I will ever build.