[TCML] Spark dynamics on Jacobs Ladder

[Kurt Schraner]

Hi Bert,

...thanks for the very lucid demonstration and formulas of the relative 
merits of the magnetic and electric field, regarding mechanical force. I 
"think" many of us "electric-people" are used to think "current flow" by 
habit, when noticing "force", instead of considering electrostatic 
attraction as well (myself included; may be, 'cause of the many motors 
around).

When doing the experiments of "Jacobsladder-Oscillator", I also made some 
calculations, which show the relative merits of electric vs. magnetic forces 
in this case:

http://www.pupman.com/listarchives/2007/Mar/msg00673.html

Best regards

Kurt

Bert Hickman wrote:
> Hi all,
>
> I just took a look at the theoretical magnetic and electrical forces
> between a pair of parallel conductors (simpler than diverging wires
> in a JL, but should be close enough). Suppose we have a pair of
> parallel wires in air with radius "a", separated by a distance "b"
> (where b>>a). The magnetic and electrostatic forces per unit length
> (in Newtons/meter) can be shown to be:
>
> F(magnetic) = Fm = Uo*I^2/(2*Pi*b)
>
> F(electrostatic) = Fe = Pi*€o*V^2/(2*b*(ln(b/a)^2))
>
> where:
> Uo = 4*pi*E-7 H/m
> €o = 8.85*E-12 F/m
> I = current flowing through both wires
> V = voltage between wires
>
> Now, suppose we plug in 0.25" diameter wires separated by 1.5", I =
> 0.030A, and V = 15,000 volts and solve for the respective
> electrostatic and electromagnetic forces per meter of electrode
> length:
> Fe = 1.33E-2 Newtons/meter
> Fm = 4.72E-9 Newtons/meter
>
> Thus, for Gary's NST-powered JL, the attractive $electrostatic force
> between the wires (i.e., when the arc is not present) is about _three
> million times greater_ than the repulsive magnetic force when the arc
> is bridging the gap. This appears to provide theoretical support for
> the experimental results described by Kurt Schraner.
>
> If we increased the arc current to 50 amperes, then the magnetic force
> becomes approximately equal to the electrostatic force at 15 kV for
> the above wire geometry. If we increased the current to 50,000
> amperes, the magnetic force increases to 1.31E+4 Newtons/meter, or
> about 1 million times greater than the electrostatic force. Since
> this force also acts upon the arc itself, the arc is rapidly pushed
> away from the source of power, as seen in the circular Jacobs Ladder
> and during some power line arcs. This phenomenon is also used to
> sweep high current arcs across electrodes (to reduce electrode
> evaporation in ultrahigh current closing switches), and within
> certain vacuum power interrupters.
> Reference: "Electric and Magnetic Forces Between Parallel-wire
> Conductors", N. Morton, Physics Education, v14 n6 p369-73 Sept 1979.
>
> Bert