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