RE: More ISSTC theory stuff (l o n g)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com> 

Hi Antonio, thanks very much for your input.

 >The big problem is to guarantee good matching for any load, what seems
 >impossible.

At first sight it does, but I think it's not really that bad. If the
streamer load is not heavy enough, the output voltage (and primary current)
will just ring up, lengthening and heating the streamers until they present
the right load. (as streamers get longer/hotter their impedance decreases,
but this impedance is inverted by the "matching network" so the impedance
seen by the inverter INCREASES)

So, if you design to a streamer length that is appropriate to the power/bang
energy you are running, I think the ringup will level off at your target
current and it will all work out.

You might argue that the system could get "trapped" in a state where the
current rings up but the streamers for some reason don't grow to limit it.
But I think this will only happen if you try to produce a streamer longer
than your inverter can handle- your IGBTs will explode before the streamer
reaches target length.

Anyway this sounds like serious non-linear math, so time for me to throw
away the calculator and get soldering ;)


 >No big problem, as
 >this can be converted to a parallel equivalent

Agreed, the only problem is measuring the streamer impedance in the first
place :( Again probably time for some experiments now...


 >I was deriving a set of exact design equations.
 >Not so complicated at the end, using the filter approach.

excellent! I think I understand, in your equation, the voltage gain (n) is
the term we use to get the desired impedance match? And you just chose the
bandwidth arbitrarily? If you choose a much wider or much narrower
bandwidth, what does this do to the resulting component values? I suppose it
would affect the coupling and the tunings of both "matching networks".


 >Not very different from the usual for a capacitor discharge coil.
Spooky :)))) In fact I have such a coil (the Tesla-2) with similar
parameters to the ones you posted- but roughly twice the primary inductance
and half the tank capacitance.

However I run my stuff on 377V DC here (240v AC mains) so if I understood
you right, the extra voltage would compensate for the higher primary
impedance, and the peak primary current would still be 100A.

(100/sqrt(2))A * (4/pi)*(377/2)V= 16.9kW flowing for 200uS= 3.3 Joules bang
energy, which is more than it had as a spark-gap coil 8-o

I'll try to run this coil as an ISSTC and get some measurements. Thanks to
your equation, I can easily calculate what the streamer load impedance
actually is, by measuring the primary current.


Steve C.