This is a multilayer Tesla Coil.  It is a still uncompleted unusual Tesla project.  It is a spark gap driven air cored resonant transformer, i.e. Tesla coil.
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This is a 500 meter roll of 2.5 mm multicore electrical wire. It is probably about 1000 turns, i.e. similar to my current 4 inch coil. It has been placed on top of my primary and is resonant at 38 kHz with the 90 nF MMC tank cap. No real attempt to tune or to optimize coupling.

Shown here with 3 inch sparks and a lot of inter turn corona and breakdown.

My plan is to optimize this to get the highest possible spark length to coil length ratio.
I plan to do this by using the same wire as above but in a multi helical coil arrangement. Using a single winding of insulated wire (the PVC will hold off a much higher voltage) and a double spacer between each helix (where the wire goes from outside in to start the next helix I hope to maintain a high standoff voltage between turns plus a higher voltage between helices.
With everything under oil I hope to be able to prevent racing arcs and allow reasonably high coupling. There will be high quenching with the 1400 bps ARSG and reasonable power of up to 5 kVA from the 4 MOT supply. I would aim for a height of one foot for the coil with 3 inch internal diameter and ?10 inch external. I would hope for 600 turns plus. Coil DC resistance is 3.5 ohms.
It will be mounted in an acrylic container filled with oil and will probably need large insulating rings to prevent surface tracking and a large insulated base to avoid primary to secondary strikes.

I now have the 60 square spacers and the square housing to contain these under oil, fixed to a large square base. The wire is ready and a toroid is available. Now just have to undertake the complicated task of winding the multiple pancake coils.
It is now 10 years later (2015) and I still have the roll of wire and plastic base and toroid. Must get around to it sometime…

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Photo Date:  2005