For the onion, use long, narrow, metallic/semi-conductive diode tape, and wind it like a ball of yarn. As x-rays scatter electrons to the next layer outward, it very quickly becomes a voltage multiplier.

Manufacture should be easy to scale up

Regarding the anode,
it can be hollow, and arranged coaxially; pump cool helium up the center “artery”, providing the majority of cooling to the part nearest the plasmoid; and vent it back along “veins” around the outside. if you can operate the helium output at 550-900°C, you can make use of IR-photovoltaics. and this can be done at fairly low pressure.

Can the anode be cone-shaped, overall?

For 2MW cooling, I’m getting a flow rate for helium coolant, with ΔT = 800°C, as .48 kg/s.
At atmospheric pressure,
that’s 3.68 m³/s at 100°C input, and 11.6 m³/s at 900°C output.

Also, I’m looking at the chart of x-ray absorption cross-sections, and notice that Carbon might not be very bad as arterial structure, graphene tubes helping conduct waste heat very quickly away from the tip, with much less radial heat flow to the helium input.

Here’s the comparison…

Beryllium
keV   µ (cm-1)
3.0     37.9
10     1.08
30     .324
100     .247

Carbon
3.0     203.9
10     4.951
30     .567
100     .339

Copper
3.0     7034
10     1960
30     96.6
100     4.06

And, if you arrange the tubes parallel to the high-energy electrons, you’ll also drastically reduce erosion. That’s what leads me to the conical shape, ~20 degree angle, to agree with the electron exit beam

Electrode design/ profile/ taper is left wide open in the patent. Made to order for marketing “advantages” and snake oil sales. Buying a FF core (swap) intelligently will also require that all parties agree on how the word Unity is used, as well as variations on true power vs apparent power. This is going to make solar panel calculations look tame and straight-forward.