Is it beneficial to use a semi toroidal DRSSTC primary coil?

[Benjamin Lockhart]

Is there much merit in using curved primary shapes to get increased coupling or better field shaping on a standard DRSSTC? (Not QCW)

For example Franzoli's coils here


Thanks, Benjamin

[AstRii]

Probably just increasing the distance between the first turn or two from high voltage on the bottom of the secondary

[Mads Barnkob]

Is Franzoli's case I would say it is purely aesthetic and maybe to make room for mounting the secondary easier.

The change to coupling from this small deviation from a flat coil, is neglectable. Those primary coils that rise so 30 or 45 degrees, have much higher coupling, but the outer turns of the primary also get much closer to the secondary top.

Unless you experiment with high coupling, flat primary will be the easiest to make and best in trade offs (easy to control coupling, less flash-over chance from distance, self-induction heating is somewhat higher) for 95% of Tesla coils.