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Re: Slow Wave Helical Resonator Experiment



Hi Terry,

> Original Poster: Terry Fritz <twf-at-verinet-dot-com>
> 
> Hi All,
> 
>     This is an old subject but tonight I repeated an experiment described in
> the paper "Tesla Coils: 1890-1990  100 Years of Cavity Resonator
> Development" by James and Kenneth Corum.  In that paper, they describe a
> phenomena where the voltage on the secondary rises by standing waves in the
> secondary after the primary spark goes out.  They describe how the Tesla
> coil behaves as a "velocity inhibited quarter wave resonator".  In this
> paper they describe the secondary voltage increasing to very high values
> after the primary spark has gone out.   Apparently over 10 times what it
> was during the ring-up period.  Those that have studied their paper will
> recognize this as being the subjects of Figures 4 and 5 in that paper.
> They also describe the "coherence time" as the time it takes for this
> voltage rise to reach a maximum.  This is under low loss or no breakout
> conditions.
> 
>     At:
> 
> http://www.peakpeak-dot-com/~terryf/tesla/misc/corum.gif
> 
> are the scope waveforms that show secondary terminal voltage (top trace
> 200kV/div) and primary current (bottom trace 100A/div) that I measured
> while repeating their described experiment on my system. This was with no
> breakout on the terminal.  The coherence time they describe should be
114us.  
> 
>     As the scope picture I posted shows, there was absolutely no observed
> voltage rise. The primary circuit quenching is clearly defined in the
> bottom trace occurring at 180uS (50us/div) on the fourth notch after the
> initial burst began. The secondary voltage at 294uS (180+114) appears very
> stable at ~70kV peak with no voltage rise or any evidence of the effects
> described in the Corum's paper.

I have good reason to think that the "lumped action during primary 
dwell" is invalid and that the secondary exhibits coherence at all 
times in the two coil system. This will be put to the experimental 
sword in due course. I am not the first or only person to suspect 
this. There may well be *minor* differences in secondary current 
distribution depending on primary geometry and this will also be 
tested. 
     I personally think the coherence scenario outlined in the paper 
would occur only when a rectangular pulse is applied to the coil. The 
primary normally drives it at Fr. This will be tested also to see if 
it accords with the theory. Perhaps you could try it using an untuned 
primary and single shot pulse generator?

Malcolm