Top load smoothness matters

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

This may be old news to many, but I think it needs to be stated 
occasionally for the benefit of those who may not have heard.

I was attempting to better the performance of my mini coil, by among other 
things, increasing the size of the top load (toroid).  I had been using, 
with good results, a 3"x6" toroid, constructed from a very smooth plastic 
donut used for cushioning shipping skids, covered with aluminum tape.  The 
resulting surface was very smooth and may be seen at 
http://www.laushaus-dot-com/tesla/minicoil.htm.

I bought a length of corrugated aluminum duct and fashioned a (roughly, 
from memory) 4" x 9" toroid.  The seam where the two ends were joined was 
covered in Al tape, and a length of Al tape was applied around the equator, 
in an attempt to smooth out the ridges where breakout is most likely.  But 
the performance of the new toroid (and other changes) was poor.  Was it the 
toroid surface or the other changes?

I went back to my original configuration with the smaller, smooth toroid, 
measured the performance, then applied a small, _slightly_ crumpled piece 
of Al foil to the side of the small toroid.  The edges were burnished and 
taped flat and there were no features even close to the size of the 
corrugated duct's ribs.  With the foil added, performance plummeted.  There 
were many simultaneous smaller streamers rather than the usual few longer ones.

At least for smaller top loads, there is no question - good performance 
requires a smooth top load.  I don't know how far this conclusion may be 
extrapolated for larger top loads, where fabricating a smooth surface is 
more costly and difficult.  I've always wondered about the skeletal top 
load construction using chicken wire or welded tubing...

I tried using 1-2 layers of duct tape over the corrugated duct to smooth 
out the ridges, but they still were evident after Al tape was 
applied.  Anyone know of an easy way?  I once used a wood filler compound 
to fill the ridges, which required a LOT of patience and sanding.  It 
ultimately yielded a nice smooth surface, but it added considerable weight 
and might not survive the drop test.

Regards, Gary Lau
MA, USA