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Mega toriods.

I realised that to get an even longer arc from my coil I would need a much bigger toroid - perhaps double the size of the existing toriod. The first idea was to get a 5m length of 12" diameter duct - but a such a toriod would be hard to transport and fragile. Also I wanted a bigger increase of the radius of curvature.

I constucted a toroid using concentric hard board rings.

This is not a true toroid, the inner curvature does not add significantly to the capacitance or the electrostatic shielding properties. This shape is much easier to build.

I use 1/4" plywood for the top, centre and bottom discs, and the two side pieces. The larger pieces are hollowed out to reduce weight, and make it easier to use connecting bolts. I then measured the required radius for each ring in situ. working out from the centre.

The hardboard rings are held apart by wooden spacers (7/8" high in the centre, then 1 1/4"high, then 1/2" high at the ends). I used hot glue to fix the first one - this was a mistake - expensive, short working time and poor joints - the next ones used "Better than nails" - the foam cream variety.

The structure is then covered with parcel tape, which gives a bit of extra strength and tear resistance, before covering it in Aluminium foil tape.

From the above you will see that I am building it in 4 quarters so that it will disassemble for easier transport and it will be possible to extend it by adding "straight" sections, as below.

Finishing

8 foot arcs - we weren't able to run it at full power but soon, soon (manic chackle off stage :)

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