copper disks

Cray still exists and are partner with IBM on at least one of the current fastest supercomputers on the planet.

The cray that was heavily water cooled was their second model, IIRC, and there is an example of it at The National Cryptologic Museum situated just on the perimiter of the NSA's parking lot.

Their third was likely the one incorporating heat pipes, as that was when they were embraced by industry.

Here is your air core toroidal bobbin, concealed in the form of jewelry:

Have seen something like that 20x cheaper, don't remember where.

Best regards, Piotr

Here they are!

Those are expensive, but I might have a use for something like that. I'm working on a thing that needs some a high-voltage high-current inductors, and big air-core solenoids will work but will leak a lot of EMI.

An air-core toroid is interesting. In a ferrous-core toroid, the field from each turn is concentrated in the core so passes through the other turns. If the core isn't magnetic, each turn makes its own field out into space, and the H field at any point is just the superposition of the fields from each turn, plus the overall 1-turn thing. L will not be as high as in a topology where the turns all couple with the same sign; it's not just a solenoid bent into a circle.

Micrometals sells powdered-iron toroidal cores of u=1, namely they leave out the powdered iron.

I might get a bunch of small surface-mount non-ferrous inductors and arrange them in a series-parallel array, and try to make the far-field H fields sort of cancel.