Re: Lower secondary cself => better performance?

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

Original poster: "boris petkovic by way of Terry Fritz <twftesla-at-uswest-dot-net>" <petkovic7-at-yahoo-dot-com>





> There's fairly strong
> empirical AND theoretical support for using as large
> a topload as
> possible as long as the terminal voltage remains
> sufficient to cause
> initial streamer formation ("breakout").
----
Agreed.(For 1 J per bang (and any given BPS rate!) one
can't use top load large like a house and expect from
such coil to throw long arcs)
----

 However,
> for a fixed bang size,
> increasing the topload capacitance reduces the
> maximum output voltage,
> so a larger diameter toroid may also require a
> smaller Radius of
> Curvature (ROC) to ensure that initial breakout
> still occurs at the
> appropriate point on resonator ring-up (more below).
> (BTW, for those who
> are very seriously interested in gaining a better
> understanding of
> streamer formation and propagation, undoubtedly one
> of the most valuable
> in-print publications on this topic is "Spark
> Discharge" by E. M.
> Bazelyan and Y. P Raizer (CRC Press, 1998, 320pp,
> ISBN 0-8493-2868-3 -
> $105 from Borders On-Line - cheap it is not...
> superb it is...).
---
Surely,this is a good book.
But,most of the content deals with monopolar pulses
(If this were ,for example, Marx bank list ..- no
better literature at the moment-OK.)
However,due to its' much complex voltage output
waveform ,TCs' arcs formation and propagation
phenomena are somewhat different  to be completely
analized the same way  like in that book.
----  

> Under the right conditions, an initial streamer
> transforms itself into a
> high current channel, called a leader, which very
> rapidly propagates to
> a distance which is governed by the amount of charge
> that is
> _immediately_ available from the top terminal.
---
Actually,a state of discharge called streamer
propagates much faster than the state called leader.
Bursts of corona streamers recorded in Mhz scope
frames,show that their importance for TC is of as
great significance as the formation of the leader
itself.
-----    


 The
> leader provides a
> conductive path for charge to be injected from the
> top terminal
> into surrounding regions of lower potential in a
> sudden surge of
> [ampere-level] displacement current. Charge residing
> in the internal
> capacitance of the resonator does not significantly
> impact the
> length of this step. Even though the more correct
> term for the streamers
> we see is probably "leaders",
---
Very short living  leaders ,yes.
I assume that becouse of TC + - output shape these are
the form of degenerated leaders.  
 
A Leader moving to and fro with respect to the coil
terminal.
---

 I'll continue to use
> "streamers" to be
> consistent with discussions on this list. Because of
> the physics
> involved, initial breakout is achieved at a lower
> voltage for a positive
> voltage excursion than for a negative one. And, once
> the initial
> streamer begins propagating, if the topload voltage
> can be made to rise
> at an appropriate rate, the leader can continue to
> propagate
> indefinitely.
----
Agreed.
---


 Both conditions can be met (at least
> for a while) in a
> Tesla Coil with a properly sized topload.
----
There,must  be somewhere  balans between 2 things for
squzing out an optimum (the longest spark):
between Size of the electrode,and the most apropriate
output voltage for bottling the longest spark up.
It wouldn't be suprising,for me, to get more than just
one optimal solution for given power input.
---   




> 
> As Gary and Duncan have surmised, charge flow is
> fundamental to the
> streamer propagation process. Once initial breakout
> begins, the distance
> that the initial streamer will travel (sometimes
> called the leader step
> length) is a function of the _amount_ of charge that
> can be made
> immediately available from a reservoir of charge.
> Because of the huge
> amount of charge residing in a charged cloud,
> individual step length may
> be hundreds of feet for a lightning leader, but for
> Tesla Coils, leader
> length would be inches or feet. In a Tesla Coil, the
> larger the
> available topload charge (Ctop*Vtop), the slower the
> rate of topload
> voltage collapse as charge is "sucked out" via heavy
> displacement
> currents flowing into a newly formed streamer, and
> the longer the "step"
> becomes.
----
This is true as well.
---



 Because of the high velocity of propagation
> (10^6 - 10^7 cm/sec
> or more) and the short duration of mthe current
> pulses, charge residing
> within the internal capacitance of the resonator is
> of limited utility
> since the intervening inductance prevents large
> instantaneous currents
> from being supplied directly to the streamer. 
> 
> In effect, during each step, an increment of charge
> is transferred from
> topload C into the capacitance of the streamer
> through a lossy,
> non-linear conductor (the plasma channel), forcing
> the topload voltage
> to decrease. If the topload voltage collapses
> quickly (small Ctop),
> further streamer growth is starved, prematurely
> ending propagation. A
> "stiffer" reservoir of charge (i.e., a larger Ctop)
> provides a larger
> slug of [take your pick: energy, charge, or current]
> necessary to
> develop a longer, hotter conductive channel. Small
> topload C = short
> step length. But wait, there's more...
> 
> If initial breakout occurred while energy was still
> being transferred
> from the primary to the secondary, the topload
> voltage recovers as
> additional potential energy is pumped into the
> topload capacitance and
> topload voltage resumes its sinusoidal progression
> towards Vmax.
---
 Recovery of top voltage and its further rise during
ring up ,for TC case,depends on the moment in a chain
of succesive 
discharges (high BPS rate),when potential is
considered.Througout succesive bangs ,TC arcs
propagate,thus adding more and more influence
(additional capacity for example) by their presence
and they are really "part of the system" as someone
said before.  
These are the most complex phenomena in examining TC
operation.
It is better,and more interesting if you ask me to
speak in terms of El. field and electrode surface and
space El.field gradients.

Regards,
Boris 

 



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