Parallel to... what?

If you have a low current high voltage DC supply like a rectified flyback transformer then you can get loud banging sparks instead of almost silent purple arcs, if you add a capacitor to the output. Make sure that it has high enough voltage rating.

Parallel to something else? What type of circuit are you talking about?

You will find the most information from Steve Ward and Gao at loneoceans.com

Generally it is the ramped DC bus voltage that makes the long spark growth possible, over a very long time, maybe up to 10ms. The sword charateristic shows above 400 kHz resonant frequency.

Has anyone estimated the conditions inside the spark - such as temperature, pressure, density...?

If we can estimate those, we can try to estimate some characteristics of the plasma.

My hypothesis is: does the "sword-style cutoff frequency" happen to match any of the characteristic frequencies of the spark plasma?

Hi,

just for curiosity, has anyone ever tried a tesla coil with a parallel resonant circuit like those used in many induction heating schemes?