Re: Base current......Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Stork,


> If, as you suggest, "As one moves up the coil, the displacement 
> current off of each turn increases (due to increased AC voltage) and 
> reduces the conduction current in the wire." where does this 
> displacwment current flow to and from off of each turn?

The displacement current density (which is dD/dt) goes in the 
direction of the E field for isotropic media.  This current basically 
goes to ground. This is why the current profile for the secondary is 
not constant.  The higher the voltage on the turn, the higher the E 
field (for constant geometry) and the higher the displacement current.


> Perhaps it's best to analyze with instantaneous power.  Basically, 
> instantaneous high base current times low base voltage equals low 
> top current times high top voltage.  Maybe there is just low top 
> current and no real displacement current in the upper coil 
> windings.  Maybe in a non sparking coil what people call 
> "displacement current" actually radiates out into the air dielectric 
> from the top load.

The bottom turn has the largest conduction current and the voltage on 
it is zero (assuming ideal RF ground) so the instantaneous current 
times the instantaneous voltage at this point is zero.  BTW, for 
normal H/D coils, the current at the top is about half (iirc) that of the base.



> Once a spark forms there is a plasma conduction channel and this 
> "displacment current" suddenly turn back into ordinary conduction current.

The displacement current density will still be dD/dt in the direction 
of the E field.  If dD/dt is positive (increasing voltage on the top 
load), the displacement current is out of the topload.  If dD/dt is 
negative (during discharge), the displacemtn current is into the 
topload (aka, return current).  If the coil in not feeding any 
current into the topload during discharge, then the displacement 
current into the topload will equal the conduction current out of the 
topload via the streamer.

Gerry R.