Jacobsladder-Oscillator

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Kurt Schraner" <k.schraner@xxxxxxxxxxx>

Hi all,

it was a certain surprise, when we noticed, that swiching a powerful 
induction coil with it's ~50kV HV side connected to a Jacobsladder, 
was developping enough E-field force, to set the wires of a resting 
JL in slight mechanical movement, _before_ a spark occured. Each of 
the 2 wires of the JL may be viewed as a 
leaf-spring-mounted-in-a-vice system, with it's characteristic 
mechanical fundamental resonant frequency.

In the following movie-clip my coiler-friend is periodically 
switching the Andiruptor on and off, in order to set it in mechanical 
oscillation with growing amplitude (~analogue to initiating a swing 
for children). But first watch this ~3MB movie:

http://twfpowerelectronics.com/~kurt/InductionCoils/P1000671.MOV


...I assume, the movie has already made you understand what happened: 
Andi amplifies the (mech.)amplitude of the JL, till a spark at the 
upper end shows up. Now he can stop switching the induction coil 
periodically (hear the sound!), because the oscillation continues by 
itself!!! The spark shortcuts the wires, collapsing thereby the 
E-field to almost zero, and the electrostatic attraction between the 
wires ceases. The wires swing to max.distance, the spark 
extinguishes, and the force reappears, attracting the wires... etc., 
etc. --> we have our "Jacobsladder-oscillator" ;-)
It can be noticed from the movie, the JL being at rest in the start, 
and never be moved by any means before starting the switching of the 
Andiruptor (watch Andi's hand). The JL itself is made of 2 massive 
copper wires of 8mm diameter and about 1.8m length. This leads to a 
low mechanical Eigenresonant frequency. The electrostatic force 
between the wires is estimated to about 0.1-1N, when applying about 
50kV HV. The following ~1.1MB movie shows the JL in it's _normal_ use:

http://twfpowerelectronics.com/~kurt/InductionCoils/P1000674.MOV

We have observed: the higher the frequency of the HV applied to the 
JL, the slower the spark is moving upwards (the Andiruptor allows 
going up to the kHz range).

We consider the "JL-oscillator" a pretty and simple demonstration of 
electrostatic force, and count our experiment -at least currently- to 
our favorites :-)

Kurt