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Re: Magnetic Quenching of Spark Gaps
From: TimRaney-at-aol-dot-com[SMTP:TimRaney-at-aol-dot-com]
Sent: Saturday, September 20, 1997 3:49 PM
To: tesla-at-poodle.pupman-dot-com
Subject: Magnetic Quenching of Spark Gaps
Folks:
Some more information on magnetically quenching sparks gaps in the primary
circuit of a Tesla oscillator. If you use a solenoid of "N" turns that
surrounds the spark gap, i.e.; the magnetic lines of force are parallel to
the flow of electrons/ions of the spark gap. Treat the spark (or arc) as a
flow of electrons as you would in a solid conductor. When the magnetic lines
of force are parallel to the electron flow, the likely result is a lowering
of the firing or breakdown potential of that gap (I'm not going to address
gap geometry here); it will not quench the gap any better.
However, if you use a gap-type magnet (permanent or an electromagnet) and
its lines of force are perpendicular to the spark gap, the magnetic field
aids in quenching the gap. Using the "motor principle," the conductor (in
this case the arc itself) experiences an upward force from the magnetic
field. This "upward force" depends on the magnet's polarity, the polarity
of the spark gap at that particular instant in the AC cycle and the magnetic
field strength.
Magnetic quenching was (and is) used to "blow out" DC arcs in heavy-duty
switches used to switch inductive loads. Same principle with the spark gap
in the Tesla coil tank circuit. Tesla used this method in his work (Tesla,
1894) and details are available in the older electrical engineering texts.
For magnetic quenching to be effective, the magnetic field must be
perpendicular to the spark gap axis. The magnetic itself should be capable
of at least 1K Gauss for the effect to be noticeable. The magnet poles must
be close to the spark gap and insulated from it. This is not easy, since
even a 15KV, 30 mA neon sign transformer will destroy any mica insulation you
may be using to protect the pole pieces. I had some success with enclosing
the spark gap in a glass tube.
I think there is more work to do along these lines. My experience has been
with systems under 1KW. The comments on the list are good, it's getting
folks thinking about this line of investigation. You never know the answer
until you try it (usually!).
TIM RANEY, TCBOR