A dual concentric magnetically driven circular Jacobs ladder. The sparks form in one spot but rotate due to the magnetic field.
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A conventional Jacobs ladder has a spark that moves up as heated air rises. But one can also move a spark by the action of a magnetic field as in this circular Jacob’s Ladder .
The photo above shows a spark to a NIB magnet (which is just under water). The arc will race around in circles and blur into a conical flame. The reason is the magnetic field resulting in a force on the current flow just like the right (or is that left?) hand rule which is the basis for electric motors.
The circular copper ring is close to the inside of a 15cm diameter toroidal ferrite magnet. This happens to be conductive (many ferrites aren’t). The S indicates the South pole is uppermost. The rotating spark does several rotations per second if the power is high enough.
Now consider a ring on the outside of the magnet to create the same on the outside. This is a little harder probably due to the direction of the field lines. However by shaping them with some external magnets (circular ferrite magnets from microwave oven magnetrons) a reasonable circular spark can be obtained. This does tend to decrease the free running of the central hole though.
The dual copper rings, large central ferrite magnet and 8 smaller ferrite’s form the basis of the dual concentric circular Jacobs ladders. The fine detail of the sparks as they jump along in short steps.
With a single electrode in the centre and enough voltage to jump 3.5 cm plus enough current to form a continuous arc, it will spin around rapidly. With a longer exposure lasting a couple of rotations everything blurs out. These yellowish arcs are much longer than the lower powered purple ones above.
Related pages
Jacobs Bi-ladder
Jacobs ladders
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External links
Circular Jacobs ladder Google+ post: Feb 20, 2012
Of course, if you have 3 kv at 500 A (1.5 MW) available then Lorenz forces are greater than gravity and heating. See this fearsome circular Jacobs ladder.
A 500 kV hot disconnect gives a massive 40 foot rising spark. No doubt a good amount of line inductance helps.
Photo Date: November 1, 2007