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Slinky Toroids

Coilers,
   I displayed a modest little fabrication  at Ed Wingate's 1996
Teslathon: The Slinky Toroid.  (Richard Hull video taped it, so to some
of you this may be old news.) You may be interested in this design if
you are looking for an alternative way to fashion smaller toroids. The
advantages are the ease, quickness, and economy of fabrication. Also,
the finished product is highly uniform..
   While scanning my brain for  alternatives, it occurred to me that a
helix wrapped and secured around a circular form may perform similarly
to  conventional toroid configurations. I entertained the possibility
that the discontinuous surface of such an arrangement may be a problem,
but proceeded nonetheless.
   I first considered fabricating the helix with copper wire wound
around a form, but the image of a ready made coil popped into my head:
The Slinky. With several samples in hand courtesy of a trip to Walmart
(~2 bucks each), I proceeded to connect each end of a single Slinky
together by utilizing the small metal clip that comes with the toy to
secure together the last couple of turns on either end. A dab of solder
secured things. It you examine a Slinky, what I'm referring to will
become readily apparent.  I now had in my possession a circular,
continuous helix, reminiscent of a large donut.
   The next step was to expand the donut and install a circular center
section, the size of which determining the final diameter of the
resulting toroid. I only made two of these concoctions: One, by hot
gluing a small cat food can (empty and washed, obviously!) to the inside
diameter of  Slinky donut #1, another by soldering the top of a large
coffee can to the same position inside donut sample #2. This produced an
8 and 12" unit. If you try the slinky method, forget soldering, simply
use a  metallic cylinder of sufficiently low profile and use hot glue.
Works perfectly.
     With toroids in hand, how did they perform? I should state that I
did not have on hand more conventional units of identical dimensions
with which to compare results. And, I did not test the 8" unit; but the
12" performed very well  a top a 4" secondary. Did the discontinuous
"surface" cause problems? I must say no. The discharge did not seem to
favor high points, but rather floated about the toroid without
prejudice. This is difficult to describe, but if your an experienced
coil man, you probably instinctively know what I'm trying to describe.
    Significantly larger units could be made by attaching the ends of 2
or more Slinkys together. Then, 2 or more of the resulting larger
toroids could be stacked on top of each other for operation with larger
systems.
   As stated above, one advantage is that they are much easier to
fabricate than anything else I've tried---literally minutes are
required. And, they look pretty neato.
   I can't supply capacitance figures at this time. This comes to mind
because I was asked about it at the Teslathon.
   Does the helix wreak havoc with tuning, the electrostatic field,
etc.? I think not. Each turn is effectively shorted out. Is breakout
voltage reduced because the surface is not smooth? Well, Tesla Coils are
not Van de Graff generators. I suspect some Faraday cage stuff is going
on here. Guessing, of course.
   In any case,  maybe my experiment will interest you.
Dave Hartwick