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Re: big plasma ball

HI Paul,
               I'm guessing that DC Cox and other professional HV firms 
would know more about this than I do but having repaired a 3' 
diameter ball, I learnt a few things that may be of interest to you:

> Original Poster: "Paul Mathus" <pmathus-at-learningco-dot-com> 
> 
>      Folks,
>      
>      I've been thinking about designs for a BIG plasma ball, maybe 8'-9' in 
>      diameter.  I was thinking of making a geodesic sphere from pvc or 
>      steel pipe, and cauking on clear plastic sheeting, or perhaps screwing 
>      on clear plexi plates and sealing with weather stripping.  It would be 
>      a bit leaky, but I imagine you could hold gas long enough for a show.  

I think strength would be a major factor as the internal gas pressure 
has to be very low. Anything other than a spherical shape might be 
a challenge for a ball that size.

>      You would then fill with argon or your gas of choice, pumping in more 
>      as needed to replace loss while you astounded the masses.  This is a 
>      possible Burning Man installation I've been tossing around for my 6" 
>      coil.
>      
>      I was wondering what the best geometry for placing a coil in this 
>      contraption would be.  If the primary was inside you would risk 
>      primary strikes from the increased spark length, no?  

Yes.

  If the primary 
>      was outside, the sphere would interfere with coupling, wouldn't it?  

No. 
      
>      Also, does anybody have any guesses/experience on the spark length and 
>      other effects you get from running a coil in an gas mixture?  Would it 
>      look similar to the typical gift store plasma ball?

The insulation which works at normal atmospheric pressure would 
be *gone*. However, the voltages at which these things work is 
nowhere near typical TC voltages. What I found was needed for the 
ball I fixed (it ran CW from an inverter) was a lot of power. The 
shunt capacitance it presented to the power supply was very high. 
You would have to take this into account when considering the use 
of a TC. In fact, you'd really need to know the range of values under 
different streamer conditions before you even started designing a 
TC to run it.
      
Regards,
Malcolm