Re: How (does) voltage rise(s?).

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:
>
> Original poster: Chip Atkinson <chip@xxxxxxxxxx>

> The first question was why one wants to loosely couple the primary and
> secondary.  Why not just have a solenoidal primary enclosing the
> entire secondary rather than a pancake or conical primary?

The first reason is insulation. Another reason is that there is no
practical solution to the problem of complete energy transfer from
the primary capacitance to the secondary capacitance with coupling
coefficient higher than 0.6.

> With the uniform solenoid field the secondary is just subject to turns
> ratio and the voltage doesn't rise any more than that.  There is no
> "whipping action" where the voltage is more or less free to rise as there
> is when only the base is driven as by a flat coil.

There is no "whipping action" in a capacitor-discharge Tesla coil.
It is just a system of two coupled resonators where the energy that
is initially in a low-impedance resonator (high currents and relatively
low voltages) is transferred to a high-impedance resonator, where it
appears as high voltages and small currents.
The ideal voltage gain in a system tuned so L1C1=L2C2 is
sqrt(L2/L1), that would be the turns ratio if the coils had identical
geometries.

> The next question in my mind is *why* does the voltage rise?  How can I
> think of it?
> Here's what I came up with -- the electrons are like a gas.  If you have a
> column of air, say, and drive it at the base you can actually get louder
> (greater voltage) output if you drive it at the resonant frequency.  For
> example, a didgeridoo.

This is closer to the case of a SSTC, where a continuous low-level input
is amplified by resonance, and in this case there is really a whipping
action. But the drive at the base is just a convenience. Could be
anywhere.

> The thing though was that doesn't the oscillating
> medium have to have momentum to resonate?  That's where I figured the
> inductor of the secondary came into play.  An inductor conceptually gives
> electrons momentum -- they keep flowing in their current direction and
> resist changing directions.
>
> The purpose of the capacitor at the top is mainly to store up this
> pressure wave of electrons until the pressure (voltage) at the top reaches
> the breakout voltage.  Then once it's broken out, the electrons are
> suddenly released and produce a more energetic streamer or spark.  The
> reason for not just having a bare wire at the top is that the point effect
> of the bare wire allows the breakout voltage to be too low.  The reason
> that we don't put a toroid the size of a box car on a 3" coil is that a
> toroid that big would "soak up" all the surplus electrons and spread them
> over such a large area that the voltage would actually drop from what it
> was right where the wire attached to the toroid.

Ok, but the top capacitance is essential part of the secondary
resonator.
Without correct tuning of both sides the energy in the primary system is
not transferred completely to the secondary system. The energy transfer
does not occur in a single pulse, but in several full oscillations.
The faster case is with k=0.6, where energy transfer occurs in a
single full cycle.

Antonio Carlos M. de Queiroz