Re: What it takes to get big sparks?

to: Scott, Jim

The spark discharge from a Tesla oscillator is a true displacement current,
and as such, does not require a "second" terminal for the displacement
current to travel to.  


> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: What it takes to get big sparks?
> Date: Monday, January 04, 1999 8:15 PM
> Original Poster: Scott Stephens <Scott2-at-mediaone-dot-net> 
> At 03:31 AM 1/4/99 -0700, you wrote:
> >Original Poster: "Jim Lux" <jimlux-at-jpl.nasa.gov> 
> >Starting with some assumptions:
> >
> >1) The actual spark develops very quickly if there is a suitable low
> >impedance source. The leader moves very very fast, essentially running
> >entire length in a microsecond or thereabouts.
> What length? The length of the arc in question? I ask because I am
> considering the mean thermal distance a positive ion can travel before a
> collision. So the leader is a conduction process, rather than a ballistic
> particle beam? What about electrons & there distance before collision?
> >3) As the spark develops, it is essentially a capacitor that has
> >capacitance (because it is getting bigger) and is charging at the same
> >time, as well as heating the air up.  This means that current is flowing
> >through this "spark capacitor".
> Any ideas on the ionization energy requirements for the arc channel? What
> are the arc channel dimensions? No doubt this is incremental, so the
> price is paid on each RF cycle rather than once as a solid-liquid or
> liquid-gas phase change. What about radiation loss?
> I don't mean to be meticulous; Just know what the numbers are within 20%
> a typical kilo-watt Tesla Coil.
> >I asked myself, where is the other connection of this capacitor?
> The potential drop of the electric field; a large concentration of
> or negative charges does not require a complementary or mirror image to
> sustain a field. Unlike the magnetic poles; which are not observed
> like electric ones are.
> >And, because we are talking fast time scales here (microseconds, again),
> >the inductance of any sort of wire connection from the bottom of the
> >to the "ground" means that the coil can't really supply any appreciable
> >current while the spark is forming.
> If you have a big shorted inductor, with a big magnetic field, you will
> unpleasantly suprised by the voltage it puts across an opening in the
> interupted current.
> >So then, what we have is an inductor (the secondary) which charges a
> >capacitor (the top load working against the ground). That capacitor then
> >breaks down (i.e. a leader forms) and discharges into the spark.
> In that order? Why?
> > The actual spark formation is almost independent of the secondary
> because the
> >current required to develop the spark is much higher than that coming
> >the inductor to the capacitor.
> That would explain some of those spikes in Terry's oscillographs. What
> those peak currents? Do they correlate to a leader burst?
> >and assuming you want your capacitor
> >to be able to discharge in something on the order of 10-100 nSec, making
> >bigger than 20-30 ft isn't going to buy you much.
> What's so special about 10-100 nSec? What are those spike width's in
> oscillographs?
> And today:
> >1) Formation of the leader (slightly luminous), very fast, requires
> >charge and a low inductance source (i.e. the top load)
> >
> Sounds like the high-voltage (4 KV), low current ionizing pulse for a Xe
> strobe light.
> >2) Development of the visible arc: requires enough energy to make the
> >hot enough to conduct, and luminous as a result, occurs much slower, and
> >can take power through a relatively high inductance source (e.g. the
> >secondary coil).
> Sounds like the low voltage (300 V) high current (100A?) pulse that flows
> after the Xenon's ionized by the high voltage. Remember my suggestion to
> research a dual-mode coil; one that gets ionized by infrequent ( < 10
> per/second) 10 Joules impulses, and heated/sustained by a sub-kilowatt CW
> coil?