Why Secondary Q Matters

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi all,
        Here are some thoughts on this topic for you to ponder. 

    There is one situation when secondary Q doesn't matter - i.e. 
when the need for it is over and done with: when streamers have 
attached to something forming an arc.

    There are two ways of generating attached streamers: the first 
when an discharge rod etc. is placed close enough to the terminal for 
an arc to form, and secondly, when an airstreamer has propagated 
through repetition to the point where it connects with an object 
considerably increasing the discharge currents and dragging the 
loaded Q down - power losses in output discharges are good :)

    Scope traces of operating secondaries show that for air streamers 
only, the loaded Q of the secondary remains relatively high. Multiple 
energy trades with the primary occur (if the gap system allows them 
to). Sparks do not propagate well if something inhibits the 
secondary's ability to ring, either continuously if the gap quenches 
at first notch (decrementing by streamer power dissipation of course) 
or through re-ringing as multiple trades with the primary proceed. In 
this second case, a high unloaded primary Q is also required. This 
can be facilitated by operating with a high primary impedance and low 
gap currents. High primary reactance at Fr is important for this to 
occur.

     Secondary Q is important for two reasons - to generate initially 
the highest possible voltage for a lump of Ep (more bang for buck) 
and to retain energy that is not consumed in discharges *over each 
half cycle of ring*.

     Typically, we want streamers to stretch out over great distances 
and connect with something. Much more exciting than placing a 
discharge rod close to the terminal IMO. In my experience, a system 
suffering from low unloaded Q does not promote streamer growth 
through repetitive primary bangs at all well. A symptom I've observed 
with such a system is that arcs cannot be formed that are 
substantially longer than the length air streamers reach. It appears 
to be a requirement for streamer propagation that prolonged ringing 
per bang is needed to heat an ever-increasing length of air.

     I'm not a great fan of matching-secondary-impedance-to-spark 
theory because the impedance of the spark is in fact going to be 
determined by both by available energy to feed it and the type of 
spark it is (air or attached). (I should qualify that by saying that 
the pressure, temperature, mositure content and molecular content of 
the gas must also be a determining factor)
    In the first case, the spark impedance is relatively high 
(witness the relatively high loaded Q of a system producing 
airstreamers) and in the second, rather low (the loaded Q of the 
system has dropped into the dirt). This is why a large terminal 
capacitance makes loud bright arcs that we all love. One might infer 
from that that the secondary is doing most of the delivering to the 
air streamers and the terminal to the arc, and we want the streamers 
to generate the long stretch prior to a connection with on object 
being made.  The scope waveforms strongly suggest this is what occurs.

I'm sure this will be regarded as a lot of unqualified handwaving in 
some quarters. It seems to be borne out in the field though. I'll be 
watching further development of more scientific modelling with 
interest.

Regards,
Malcolm