I'm trying to build a Tesla coil but in my country find the necessary parts for this is extremely difficult. Currently I have everything but the top capacitor.
I want to use a toroid, but find a perfect one is no possible, so I'm building it from a metal pipe. The upside view will be like an octagon.
My questions are:
You don't mention how big the Tesla coil is, or the diameter of the pipe you want to use for a toroid. The problem with an octagonal pseudo-toroid is that there will be sharp edges on the seams that could lead to corona leakage, reducing the resulting arc length.
I generally use flexible aluminum ducting made for clothes dryer venting, and I cover it in aluminum foil tape to smooth out the edges. This is actually a very common method, and is very popular due to its low cost and ease of sourcing the parts.
I fill in the inside of the toroid with aluminum pie plates, and connect the top wire of the secondary coil to the plate. This ensures there is a good electrical connection between the secondary coil and the topload.
The final topload looks something like this (not my image):
Tesla was very practical in his work. He has made all components himself using rudimentary tools. As for your capacitor, an aluminum foil and some support is enough.
