Toroids

The definitive words "power toroids" tell much of the tale on
this approach....

At ultrasonic frequencies and higher, toriods are widely used
for both RF and for power conversion. These are generally
formed of cemented ferrite particles, which work well at these
high frequencies.

Toroids are widely used (were?) in telephone lines, as components
of audio filters. Their power handling is in the milliwatt range,
however.

You'll find toroidal transformers in PC power supplies, but
these are operated at ultrasonic frequencies as either power
oscillators or power amplifiers - the 60 Hz (or 50...) input
current is rectified to DC, then "chopped" at an ultrasonic rate
to make AC, which can then be converted from the 100-odd volts
at input to the various output voltages needed.

These toroids wouldn't be suitable for operation directly at line
currents, as at 60Hz, they would saturate (fail to do their job,
heat up etc.) at very low current levels. Worse at 50Hz.

The amount of Iron is decreased as the frequency goes up
which is why 400Hz is found in aircraft power systems.
Less weight to get off the ground.

But I stand with the others - if you can find power toroids
suitable for AC mains operation at the power levels you
need, it might be fun to wind a few hundred or thousand
turns of wire. I'd rather be making chips, myself.... / mark