Mark,
The primary is at the wide, trumpet-bell end of the secondary.
That is intentional. The broad end is the current/magnetic end of the
resonator, while the narrow end is the high-potential/electrostatic end.
So the increasing inductance toward the bell is not remote from the
primary; it is directly adjacent to it. Your observation that inductance
grows strongly with radius is therefore consistent with the intended
geometry rather than a coupling problem.
I should have made the primary location explicit in my earlier description
of the apparatus.
David W. Thomson
On Thu, Aug 27, 2026 at 11:15 AM Mark Rzeszotarski via Tesla <
tcml@xxxxxxxxxxxxxxx> wrote:
> My concern with this geometry is that the majority of the coil
> inductance will be at the trumpet end, far from a primary coil. This
> would make it difficult to couple sufficient energy into the secondary
> when the primary is positioned near the small diameter portion of the
> secondary.
>
> I once built a flat spiral secondary with a helical primary around it.
> The voltage rise in the secondary was greatest in the few outer turns,
> giving rise to significant arc-overs. Inductance depends on the radius
> squared so most of the inductance will be in the trumpet bell.
>
> Mark Rzeszotarski
>
> --
> Mark S. Rzeszotarski, Ph.D., FAAPM, DABR
> Emeritus Professor of Radiology
> Emeritus Professor of Biomedical Engineering
> Case Western Reserve University
> Cleveland Ohio, U.S.A. 44109
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