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Re: Why does top capacitance work? (fwd)



---------- Forwarded message ----------
Date: Mon, 24 Feb 1997 11:05:07 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: mod1-at-pupman-dot-com
Subject: Re: Why does top capacitance work? (fwd)

Hi Ed, all,

<snip>
>  > voltage. Ultimately, it IS power which governs ultimate streamer length.
>  > 
>  > Certainly your last point is true, although Wysock and Cox's coils tend
>  > to have BIG tank caps, small primary inductance and small top
>  > dischargers -- Adding tank capacitance alone seems to be sufficient for
>  > BIG streamers on larger coils. 
>  > 
>  > Looks like there are still lots of mysteries to be solved! BTW, what do
>  > you do for a living that lets you play with these nice toys?? :^)
>  >
>  > -- Bert --
>  
>      This is something that I am hoping to investigate. It is not true 
>  that all systems will benefit from extra capacitance in the primary 
>  system. One very experienced coiler reported that increasing his Cp 
>  from 0.1uF to 0.2uF resulted only in burning up the gap faster with 
>  no extra output length (power went from 25kW to 50kW). Others have 
>  also noted this effect. The question then is: why does doing this 
>  benefit some systems and not others? I earlier suggested that this 
>  might well be a function of the secondary characteristics and that 
>  there is an ideal primary configuration for a particular secondary. I 
>  will be looking for evidence of this in the coil design notes kindly 
>  sent to me by some list members.
>  
>  Malcolm
>   >>
> Malcom,
> 
> Is it possible that this is the same phenomena as just adding more power to a
> given system and getting little or no increase in output?  I have reached
> that point with my 6" dia coil.  Once you get up to about 4kva in, adding
> power up to about 7kva results in little increase in output.  I believe there
> is a power or performance curve for any given coil system that is based
> primarily on the physical size of the secondary - given a well designed
> system, i.e. good primary, in tune, good quenching gaps, good Q, etc.  As you
> would expect, the curve starts out rather steep where doubling the input
> power results in considerable increase in output (discharge length).  Then
> gets to a point where the curve gets quite flat and little output increase
> can be had even by doubling the input power.
> 
> Comments?
> 
> Ed Sonderman

That is exactly it. Doesn't make much sense from the angles we've 
been exploring so far does it? With a bit of luck I might just find 
out why when I have completed the exercise which will still take a 
couple of weeks. I have over thirty designs to analyse thanks to 
everyone and there is much calculation needed to extract the 
quantities which I am examining - in fact the chart I am drawing up 
is enormous.
    In the meantime, I seriously suggest going to a terminal, 
not necessarily with more capacitance, but a much bigger radius of 
curvature. I suspect the limit has to do with the degree of output 
ionization reaching that which imposes more-or less continuous
loading on the secondary. I consider this to be very important, so
much so that I am currently building a terminal for my large 
resonator (and smaller ones) that has exactly that attribute. For 
toroid makers out there, I am talking about the diameter of the pipe 
from which the toroid is made, not the actual toroid diameter. The 
limit for ROC is a sphereoid shape.

Malcolm