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Re: RFI source tests...

Hi Terry, Bert, All,
 I came across an article that might contain information relevant to
your present interest in mitigating spark gap noise.  The scope trace
in the article indicated a delay step in the spark gap.  The trace
looked smooth and without noise spikes. This might also be useful for
quenching the primary.  A lot of unexplored territory here wrt Tesla
coils.  If anyone has the follow-on article to this one, that would be
very interesting reading.

Barry

USING MAGNETIC PULSE SHAPING TO REDUCE SPARK GAP LOSSES AND ELECTRODE
EROSION, by Michele Wofford, Mary Baker, Magne Kristiansen, at the
Pulsed Power Laboratory, Electrical Engineering Department, Texas Tech
University, Lubbock, Texas, IEEE number of article is
CH3180-7/92/0000-0289$1.00 C 1992 IEEE.

All that I know about the article is that it may have come out of a
POWER MODULATOR SYMPOSIUM around 1992.  I believe that there is
someone on this list that has access to the Mother Data Source at
Texas Tech (hint hint).

ABSTRACT

 Spark gap electrode erosion is due in part to the product of the gap
voltage and current.  As the spark gap breaks down, the intitial
voltage has not fully dropped before the current begins to rise, and
the VI product in this initial phase can be quite high.  If the
current can be delayed until the discharge channel is fully formed,
and the voltage has dropped, the VI product can be signifigantly
reduced.

 In previous studies on spark gap electrode erosion, one of the
parameters was to include magnetic pulse shaping (1).  A signifigant
reduction in erosion resulted from using a saturable reactor to delay
the initial current through the gap.  Recently, the same method was
applied to a vacuum switch, and the turn-on and recovery
characteristics of the switch were improved (2). (might keep the
Victoreens cooler?)

 Based on these findings, further studies will be conducted to explore
the connection between magnetic pulse shaping and spark gap erosion
and operating parameters.  The work will focus on the loss mechanisms
in the turn-on stage of spark gaps.  This paper will describe the
initial effort of the experiment, including the test arrangement,
diagnostic techniques, and preliminary data.
......
 The measured saturation delay with 32 (ferrite cores) is 200 ns.
......
 Damping resistors Approx. 1 ohm in series with the switch (reason not
described??)
......
 ....A bias winding for all of the ferrites would have been
cumbersome, so some degree was achieved by allowing the pulse to
oscillate through several cycles.
.....
 Conclusion:  Previous research has shown that the use of saturable
inductors signifigantly decreases the power loss, and consequently
electrode erosion, in spark gaps.

(1) S. Levy, "Spark Gap Studies", U.S. Electronics and research
Development Laboratories, Fort Monmouth, New Jersey.

(2) R.A. Dougal, G.D., Volakakis, M.D., Abdalla, "Magnetically Delayed
Vacuum Switching", 6th IEEE Pulsed Power Conference, 1987.


> It may be possible to use ferrites between the individual spark-gap
> elements to slow down the dI/dt once the heavy main conduction
begins,
> but it's not obvious how the dI/dt can be appreciably reduced for
the
> discharge current associated with an individual gap's
self-capacitance.

> -- Bert --

  As I suspected, the initial spike is
 composed of very high frequency RF. Cheers,
> >
> >         Terry