"1/2 Wave Bipolar Tesla coils"
Bipolar Tesla coils are Tesla Coils have 2 discharge terminals. They
are connected to each end of the secondary. Discharges eminate from one
terminal to the other. The primary coil is placed in the center of the
secondary coil. The secondary coil is 1/2 wavelength long. The discharges
from each terminal are 180 out of phase, so the discharges attract each
other. They do not necessarily require grounding, the secondary coil can be
left to work against itself.