stepped leaders (was Safety FAQ...)

To: tesla-at-pupman-dot-com
Subject: stepped leaders (was Safety FAQ...)
From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
Date: Sun, 18 Aug 1996 20:33:57 -0500
>>From leyh-at-ix-dot-netcom-dot-comSat Aug 17 22:44:23 1996
>Date: Sat, 17 Aug 1996 16:00:43 +0000
>From: leyh-at-ix-dot-netcom-dot-com
>To: tesla-at-pupman-dot-com
>Subject: Re: Safety FAQ is here -- draft, asking for comments.

>Malcolm Watts wrote:
>> 
>> Hi Robert, all,
>>                  I'm afraid I can't agree with your hypothesis....
>> 
>> > I believe that the phenomenon which is being bandied about where some
>> > people believe that the discharge channel is growing on itself is
>> > completely illusory and false. 

>(snip)

>> The problem is when you consider the phenomenon using (a) synchronous
>> breaks, and (b) using static gaps. My large coil with its current
>> (npi) gap setting produces a streamer about 11" long when operated
>> single shot, 4ft+ when repetitive. Greg Leyh had some info on this
>> that you may have seen (although he was using async rotary).
>> 
>> Regards,
>> Malcolm

Greg wrote:

>I would like to offer two observations that tend to support the 
>'arc growing on itself' theory:

>A:  In Uman's famous book 'Lightning' (Dover Books, 1969), there are many
>nifty streak camera photos that show natural lightning actually propagating downwards,
>in small segments called 'stepped leaders'.  According to the author, each successive
>stepped leader adds 10 to 200 meters to the propagating end of the arc, at
>repetition rates of 100 Hz to 20kHz.  The rep rate is determined by the capacitance
>of the cloud, which acts somewhat like a relaxation oscillator.  

I have this book by Uman and am familiar with the stepped leader theory.
I also have a book by Schonland, "The Flight of the Thunderbolts", 
1964, Clarendon Press, Oxford.
  
I don't believe that phenomenon occuring on the enormous scale of stepped
leaders in natural lightning are necessarily useful in the explanation of 
phenomena observed in Tesla coil  discharges. 
The smallest stepped leaders in naturally occuring ligthning are at a minimum,
at least an order of magnitude larger in scale than the biggest Tesla coil sparks
yet produced. The features of a Tesla coil streamer advancing upon itself in
small steps is absolutely microscopic compared to the stepped leader lightning
example referred to here by Greg.   Sorry folks,  I don't buy a small scale stepped
leader connection here for Tesla coils as based on the natural lightning example.

>B:  I have noticed that the spark length from the toroid is a strong function
>of rotary gap speed, where the output arcs at full speed (300pps) are almost 
>twenty times longer than at those at tuning speed (1pps). 
>And although the gap isn't synchronous, there's nothing for it to be
>synchronous with, as the power supply for the primary is DC in this case.
>It is possible for the gap firing rate to beat with the ripple on the DC supply,
>but the ripple is not be larger than 14% of the supply voltage, since it's derived
>from full-wave rectified 3-phase.  The ripple would have to be around 95% for the 
>beat frequencies to account for the 20 to 1 growth in the arc length.

>-GL

I have had no lab time with DC powered or synchronous powered T.C. 
systems to be able to comment meaningfully here.

rwstephens