Re: [TCML] (somewhat) high speed plasma photos from coil/capacitor interactions

[Bert Hickman <bert.hickman@xxxxxxxxxx>]

Hi Josh,

Very interesting images, including the others at:
http://gallery.vandervecken.com/v/tesla/second-coil/capacitor-bank/axe-apr10/ 


As I understand your system, you're elevating the secondary base to 
several thousand volts DC via a small HV supply and using a 100 uF 
energy storage capacitor connected in series between the base of the 
secondary to RF ground. When the topload sparks to ground, it also then 
discharges the energy discharge capacitor through the secondary with a 
high current, low frequency (many 10's - 100 Hz) oscillatory "power arc" 
that may persist for 10's - 100's of milliseconds. The discharge current 
is limited by secondary winding inductance and resistance, and the 
dynamic resistance of the arc channel itself. Based upon the physical 
size of your secondary and arc length, this is likely 20-50 amps. The 
resulting arc-like discharges flow along the smaller spark trails 
initially blazed by the Tesla coil ground discharges.

In the top photo on the page you referenced, you're seeing several 
residual "plasmoids" left over from a recently extinguished arc 
discharge. These glowing regions are commonly captured in photos of 
high-power Jacobs ladders right after the arc "breaks". The other images 
were taken at earlier times during the high-current discharges where 
more of the arc plasma was excited. Some portions of the extinguished 
arc (constricted regions or sharp bends) don't cool down quite as 
quickly, and the thermally-excited air molecules in these regions 
continue to glow for a longer time than other portions. The hotter the 
original arc, the longer the plasmoid lifetime. These plasmoids are 
often observed in laboratory-created "ball lightning":
http://www.ipp.mpg.de/ippcms/eng/presse/pi/05_06_pi.html

Similar plasmoids occur in "bead lightning", where regions of isolated 
glowing plasma remain for hundreds of milliseconds after the main stroke 
has ended:
http://wvlightning.com/plains2005/june14h.jpg

BTW, be extremely careful - you have a true "killer system" there...  =:^O

Bert
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Josh Bailey wrote:
> Evening all;
>
> http://casuallethality.com/?p=683
>
> Friend Mike Kennan and I have been experimenting with discharging a
> relatively most capacitor bank (100uF, 4.5kV) with a relatively modest
> Tesla coil (rotary gap, 8kV/60mA primary).
>
> Above are some (I think) interesting photographic results. All are light
> triggered, "ISO" 3200 1/3000 and 1/4000 digital SLR shots - the camera is
> triggered by a sensor/microcontroller combination (the flash of the bank
> discharging).
>
> To me the most interesting is the first, with two fairly luminous areas
> and one probably very recently luminous (far left, next to topload).
>
> Care to conjecture on the forces at play here?



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