The goal of a toroid on the top of the Tesla Coil is to prevent ionization.
This is achieved with a large highly conductive object that has a smooth
exterior. Any flanges or convolutions should be removed, if possible. There
should be NO insulation near any exterior surfaces as this impedes the
uniform field near the surface of the toroid. The toroid must be
non-magnetic (non-ferrous) so it doesn't act as a magnetically coupled
shorted turn to the secondary coil. If you get stationary corona discharge
from any specific point, you probably have a surface defect that needs to
either be smoothed down or filled with conductive material. You may need to
increase the diameter of the material used to form the toroid: example 8" AL
tubing formed into a 24" donut, increase tubing size to 10" or 12".
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxxxxxx
https://www.pupman.com/mailman/listinfo/tesla