No, you don’t need capacitance see ringing. a simple RL circuit will act as a low-bandpass filter, and the ringing is just the sum of some higher harmonics of the square wave. You see ringing in an RLC circuit if your power supply is DC, but we’re working with AC here.

For an RL circuit, the bandpass is R/(2piL).

]]>LOL, you have an RL circuit, but that can still be a low-bandpass filter.

]]>The decaying ringing looks very much like the result if you’ve got a low bandpass filter. The result pulses are basically the square wave, fourier transformed, cut out a buncha high frequency stuff with a heaviside function, then inverse fourier it back.

Since you have an array of caps in parallel (IIRC) this totally makes sense, it looks like a canonical discrete low-pass filter. You may want to take the analytical solution of the RC filter equation and see if it matches up with the highest frequency in the graphs. Email me if you want me to give the math some effort.

]]>The inductance of a (multiple turn) wire loop depends on N^2 (N = number of turns) so the inductance of 1 loop with 60 turns is not the same as 6 loops with 10 turns. If the coils were totally independent the total inductance would be about 100 μH.

The coils are definitely close enough for mutual inductance to change that number, but I’m not sure exactly how… (does the opposing coils increase or decrease the inductance?)

The inductance of a (multiple turn) wire loop depends on N^2 (N = the number of turns) so it’s a big difference between 1 loop with 60 turns and 6 loops with 10 turns. If they were totally independent the coils would be about 100 μH, but they are definitely close enough for mutual inductance to change that number (no idea of how much though)…

]]>Not exactly, 6 groups of 10 turns is not the same as 1 of 60 turns. If you put 10 turns into your calculator and then multiply it by 6 (in series) it will give you a smaller result (closer to real) but possibly not hugely different.

The lead in wires will also add to the inductance.

The ringing you see is due to some capacitance , possibly from the coil to the chamber and can be calculated from the frequency once you know the exact inductance. ]]>

Ray: awesome work!

I’ll try and get this spice model running myself.

]]>I would appreciate it if you would review the values (or the circuit) and correct them; since my waveform doesn’t conform to well. I will rerun if you want. That’s the nice thing about simulations; once set up they can be run over and over.

Also note that there is no reason in this circuit for the spike on some of your pictures; since that allows large currents I would suspect the inductance failing. Either shorted winding or interaction with plasma.

The failure of inductance can be tested with a pickup coil to see if the magnetic field actually goes up at that time.

Ray

Wave form:

]]>not sure about Mac; it’s in lots of linux distros so it shouldn’t be too hard to build

it is really great for getting some quick and dirty estimates; especially from old reports that might just have plots, but no tables

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