RE: Magnetic quenching.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Thomson" <dave-at-volantis-dot-org> 

Hi Marco,

 > Well, I also meant "have you noticed any difference"? You are saying
 > that you did notice "louder operation". Good.
 > Now, could you check if the gap threshold voltage has changed? For
 > instance, you could feed the gap just straight from the NST, through the
 > variac. Crank the voltage up until the gap fires. Do it with and without
 > the magnets, Any difference?

I tried your experiment.  I used just the 15kV NST, spark gap (with and
without magnets), and variac.  The gap was set at about 1/2".  Assuming that
my variac is accurate and that my supply voltage is 120 volt I received the
following results:

with magnetic quenching:
	spark began at 8.505kV (68volt on the variac)

without magnetic quenching:
	spark began at 9.12kV (73volt on the variac)

The sparking with the magnetic quench was noticeably louder with more
"popping" sounds.  The sparking without the magnetic quench was noticeably
quieter and smooth running.

This makes perfect sense when the equation I provided is used...

magnetic_flux / gap_potential = time_between_sparks (quench time)

The quench time is increased as the gap potential decreases.  This causes
more energy to cross the gap when it does fire.  It is also consistent with
the observation by Tesla and others that streamer length increases with a
lowering of secondary frequency.  As the quench time increases, the gap rate
decreases, which in turn should lower the overall system resonant frequency.

 >  >  > Can you post more information about your magnetic gap arragement?
 >  >
 >  > http://www.tesla-coil-builder-dot-com/images/sparkgapmagnetic01.jpg
 >
 > They look like magnetron magnets, am I right? You have obviously also
 > tried to rotate the upper stack relative to the bottom stack (repulsive
 > fields vs. concurrent fields). Any difference?

I believe the magnets are NIB (NdFeB).  I bought them from Forcefield, the
same place Terry buys his.  The magnets on top are three 1.5" diameter x
3/8" with .5" holes, there is also a 1" diameter x 3/8" solid disk magnet
under the top stack which is not visible. The magnets on the bottom are two
1.5" x 1.5" x 3/8" squares.  I have not tried to oppose the magnetic fields.
It's too risky without building a strong clamping device.

 > What I am trying to understand here is, is magnetic quenching just
 > bettering quenching or also rising the gap threshold voltage? How the
 > magnetic field has to be oriented?

It would be good for the books to try an opposing magnetic field spark gap.
But it is not something I'm planning to do in the near future.

It would appear that the magnetic quenching actually lowers the threshold
potential.  We also need to consider that this experiment was not done with
capacitance on the spark gap terminals, as it is in a Tesla coil.

I agree with someone else's suggestion that magnetic quenching could assist
RSG efficiency.  I also believe that making the spark gap terminals as
spherical balls will also help.  As soon as I can find someone with a welder
I'll assemble such a spark gap and test it.

Dave