Re: magnetic fields in spark gaps

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

Original poster: FIFTYGUY-at-aol-dot-com 

In a message dated 5/28/04 9:27:41 PM Eastern Daylight Time, tesla-at-pupman-dot-com
writes:

 > Would someone have a picture showing this kind of effect? Or all is
 >  really just talk?

     I recall seeing an old-time drawing of an electric-arc heat source
(forgot the application), but it used a large-ish horseshoe-shaped 
electromagnet
(about a foot in diameter) to focus the arc down into the workpiece.
     I tried this once (back in high school), but I used a solid mild steel
core of 2" x 1/4" flatbar and fairly few windings (one loose layer of about 26
ga wire IIRC), and it actually worked to some degree. I was plugging into the
120 wall current, so duty cycle of the electromagnet was low... I think I was
using it to melt things like alumina dust, seeing if I could get garnets or
rubies (wishful thinking!)
     Obviously, the electric field changes in phase with the arc's current
flow (if it's a 60Hz arc), so the arc is constantly pushed in one direction.
Sorta like a "universal" motor.
     From an induction coil, isn't the output pulsed DC? Therefore a permanent
magnet would push or pull the arc, depending on polarities involved (as we
have Tristan Steele's testimony here). Same for Van Allen Radiation Belts, TV
deflection yokes, magnetrons, etc. But an AC arc would alternately be pushed
then pulled - I wonder if the arc would be "split" or appear wider.
     Another thing to consider would be the effect on initiating the arc as
well as quenching. Is it harder to spark across a gap if there's a strong
magnetic field lengthening the conductive path before it's established? I 
presume
the avalanche electrons and ions would have to follow the same wider path, and
thus make it equivalent to a wider (non-magnetic) gap.
     Perhaps then an electromagnetic system with the electromagnet windings in
series with the current through the gap would allow spark establishment with
little magnetic field, increase the magnetic field in proportion to the arc
current, and keep the duty cycle of the electromagnet low. But obviously 
there's
many good reasons why nobody would put a big iron-core electromagnet in
series with their SGTC primary circuit. If you use a large external 
electromagnet
across your sparkgap, you might as well cut your toroid in half, throw away 
the
secondary, and finish building your cyclotron. :) Maybe you SSTC guys could
use the Hall Effect with your IGBT's, though? ;)
     Do the arc chutes over the contacts in industrial disconnect switches and
contactors use a form of induced magnetic quenching? I've always wondered why
they go through the trouble to put insulated metal horseshoe strips in those.
Would this be applicable to SGTC's?

-Phil LaBudde