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Re: [TCML] "Means for increasing the intensity of electricaloscillations" The Tesla Superconductor of 1901
On 4/12/11 8:29 AM, Carl Noggle wrote:
All true, except that I would disagree that the spark gap resistance
is a major factor. The current in the primary of a moderate sized TC
(mine, at 1600 watts, for example) is of the order of 100 amps. Going
through a spark channel that is a fraction of a mm in dia gives a very
high current density, not too different from lightning. A plasma at
these current densities has a resistivity that is lower than any
metal. A spark gap is a remarkably good switch for high currents.
Uhh.. not really. It's a good switch (and fast), but not as good as
metal. There's the cathode drop of several tens of volts plus the IR
loss in the spark channel. A lot of research says that the spark/arc is
about 7000K, so you can go look out the bulk resistivity. .
the lightning channel (per Uman) is on the order of 1cm diameter,
carrying some tens of kA. If our spark gap is 1sq mm, that's 100 times
smaller, corresponding to some hundreds of Amps. (I don't know that TC
primary currents actually get that high... The L is too big)
Most authors (e.g. Uman, Rakov, etc.) give energy dissipated in a
lightning stroke on the order of 3-10 kJ/meter over a few tens of
microseconds: that is, 5kJ/20E-6 = 250 MW. So can figure it out.. 250E6
= 20E3^2 * R => 250E6/400E6 or around an ohm/meter.
say it's 1square mm and 1 mm long.. That implies about 100 ohms/meter
for the spark in the gap, or 0.1 ohm for a 1mm long gap. 1 sq mm =
0.0015 sq inch ( that's roughly AWG 17)
A foot of AWG10 wire has a resistance of about 0.001 ohm. AWG 16 has 4
times the resistance, and is fairly close to the diameter of the spark,
so 0.004 ohm for 300 mm, call it 0.004 milliohms...
Orders of magnitude less than the resistance of the spark.
The main source of resistance in the pri circuit is the coil wire, due
to the very shallow skin depth. The bigger the better, stranded might
help a little, the best would be a lot of small insulated wires
bundled into Litz wire, but who wants to go to that much work?
A fair amount of research (in the archives) has shown that for round
numbers, about half the primary power is dissipated in the sparkgap.
I think the Litz wire approach has also been discussed.
An interesting thing to be gleaned from the table is that the RF
resistance of any reasonable wire used for the secondary will have
hardly any increase of R at TC frequencies, so the ohmmeter resistance
of the secondary is the RF resistance. The secondary coil Q should be
high too. It seems that losses in the TC are small, and almost all
the energy should be going into the coronas. If you look though them
in the daytime, you can see quite a bit of heat distortion, even
though it's hard to see the sparks themselves.
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